Court Opinion

ID: 7803568
Source: CourtListenerOpinion
Date Created: 2022-08-25 17:01:17.648746+00
Date Added: 2024-06-11T16:29:40.338452
License: Public Domain

USCA11 Case: 20-13218    Date Filed: 08/25/2022   Page: 1 of 42

                                                   [PUBLISH]

                          In the

         United States Court of Appeals
               For the Eleventh Circuit

                 ____________________

                        No. 20-13218
                 ____________________

UNITED STATES OF AMERICA,
                                             Plaintiff-Appellee,
versus
PATRICK EMEKA IFEDIBA,
NGOZI JUSTINA OZULIGBO,

                                       Defendants-Appellants.
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2                    Opinion of the Court                20-13218

                  ____________________

         Appeals from the United States District Court
            for the Northern District of Alabama
         D.C. Docket No. 2:18-cr-00103-RDP-GMB-1
                  ____________________

                  ____________________

                         No. 20-13303
                  ____________________

UNITED STATES OF AMERICA,
                                              Plaintiff-Appellee,
versus
NGOZI JUSTINA OZULIGBO,

                                    Defendant- Appellant.
                  ____________________

         Appeals from the United States District Court
            for the Northern District of Alabama
         D.C. Docket No. 2:18-cr-00103-RDP-GMB-4
                  ____________________
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20-13218                 Opinion of the Court                           3

Before JILL PRYOR, BRANCH, and ED CARNES, Circuit Judges.
JILL PRYOR, Circuit Judge:
       Siblings Patrick Ifediba and Ngozi Justina Ozuligbo appeal
their convictions for health care fraud and related crimes. Ifediba,
a physician, operated a clinic called CCMC1 and employed Ozu-
ligbo, a licensed practical nurse, there. The evidence at trial showed
that CCMC prescribed large quantities of opioids to patients who
had no medical need for them and ran an allergy-testing and treat-
ment scheme in which it required insured patients to undergo al-
lergy testing and prescribed them medication despite their negative
allergy tests. The clinic billed Medicare and private insurers for the
tests and treatments.
       Ifediba and Ozuligbo were indicted on substantive counts of
health care fraud, conspiracy to commit health care fraud, money
laundering of the clinic’s unlawful proceeds and conspiracy to com-
mit that crime. Ifediba was indicted for unlawfully distributing con-
trolled substances for no legitimate medical purpose and for oper-
ating CCMC as a “pill mill” to distribute the controlled substances
to patients who had no medical need for them.

1
 In the record, CCMC is referred to both as “Care Complete Medical Clinic”
and “Complete Care Medical Clinic.”
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4                      Opinion of the Court                 20-13218

       Before trial, the court excluded Ifediba’s evidence of good
care he provided to his patients because it was intended to prove
that his medical practice was legitimate. It also excluded Ozuligbo’s
evidence that cultural norms of their Nigerian heritage required
her to obey her older brother, Ifediba. During trial, the district
court dismissed an alternate juror when it came to light that the
alternate had independently researched the case outside of court
and discussed the case with coworkers. Though Ifediba and Ozu-
ligbo asked the court to question the remaining jurors individually
to discover whether the alternate had discussed her research with
them, the court instructed the jury collectively instead. The court
denied the defense’s motion for a mistral. After a three-week trial
featuring testimony by CCMC patients, medical experts, and law
enforcement officials, the jury convicted Ifediba and Ozuligbo on
all counts. The court sentenced Ifediba to 360 months of imprison-
ment and Ozuligbo to 36 months.
       Ifediba appeals the district court’s exclusion of his good-care
evidence and its decision to address the jury collectively rather than
individually. He also challenges the sufficiency of the evidence sup-
porting those of his substantive health care fraud convictions that
were based on evidence from medical records rather than patient
testimony. And he appeals his sentence by disputing the district
court’s drug-quantity calculation on which the sentence was based.
Ozuligbo appeals the court’s exclusion of her cultural-defense evi-
dence and the sufficiency of the evidence supporting her health
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20-13218                      Opinion of the Court                            5

care fraud conspiracy conviction. After careful consideration and
with the benefit of oral argument, we affirm.

                         I.       BACKGROUND 2
       In this section, we briefly introduce CCMC’s controlled-sub-
stances distribution practice before focusing on the clinic’s allergy
fraud scheme, which was the basis for the health care fraud convic-
tions. We then discuss the juror misconduct issue that arose at trial
and the district court’s resolution of it. Finally, we describe the de-
fendants’ convictions and sentences.
A.     CCMC Operated as a Pill Mill and Required Insured Patients
       to Undergo Allergy Testing and Treatment.
        Ifediba and his wife, Uchenna Ifediba (“Uchenna”), also a
physician, were the only physicians at CCMC. Neither Ifediba nor
his wife specialized in pain-management medicine, but they wrote
many prescriptions for controlled substances—opioids, like oxyco-
done and fentanyl, and benzodiazepines, like Xanax. CCMC at-
tracted patients who were willing to wait over three hours in a
dirty, crowded waiting room to receive prescriptions for controlled
substances. The clinic stayed open until 10:00 PM to accommodate
them. After law enforcement received tips that CCMC was

2
 Because Ifediba and Ozuligbo challenge the sufficiency of the evidence sup-
porting some of their convictions, we recite the facts in the light most favora-
ble to the jury’s verdict. United States v. Monroe, 866 F.2d 1357, 1365 (11th
Cir. 1989).
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6                      Opinion of the Court               20-13218

prescribing controlled substances to people who did not need
them, the clinic became the subject of a Drug Enforcement Agency
(“DEA”) investigation.
        Besides its opioid distribution, CCMC roped patients who
had insurance into an allergy fraud scheme. The allergy scheme be-
gan after Ifediba met Clement Ebio. Ebio connected CCMC with
Allergy Services of North America (“ASNA”) and coordinated a
joint undertaking by the two organizations. ASNA would provide
the allergy-testing equipment and immunotherapy treatments, and
Ifediba, through CCMC, would bill patients’ insurance for the al-
lergy services.
       The scheme was a simple one. Every insured patient who
came to CCMC had to fill out a questionnaire on allergy symptoms
before seeing the doctor. No matter the patient’s answers, an al-
lergy technician performed a skin-prick allergy test on the patient.
Regardless of whether the test results were positive or negative,
Ifediba prescribed immunotherapy to treat allergies and directed
the technicians to order the medication. Some patients without al-
lergies actually received immunotherapy treatment; others did not.
Either way, CCMC billed insurers over $500 per test and over
$2,000 per patient for immunotherapy. By contrast, CCMC did not
perform allergy tests on uninsured patients.
       Ozuligbo had been working as the clinic’s office manager,
but Ifediba told Ebio to hire her as an ASNA allergy technician.
Ebio balked at the request because ASNA had enough technicians
and Ozuligbo would be paid twice as much as the others. He
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20-13218                     Opinion of the Court                             7

eventually relented, however, accepting that bringing her on was
part of the “cost of doing business” with Ifediba. Doc. 251 at 85. 3
         As an allergy technician employed by ASNA but working
on-site at CCMC, Ozuligbo was responsible for patient intake,
drawing blood, performing allergy testing, and administering im-
munotherapy. She determined which insured patients would be
tested after contacting patients’ insurers to confirm coverage of the
allergy tests and treatment. When a patient came in for an appoint-
ment, Ozuligbo filled out the paperwork required for the allergy
test. If the patient expressed reluctance about taking the test, Ozu-
ligbo persuaded him. At least one reluctant patient understood the
allergy test to be “part of the process to see Dr. Patrick [Ifediba].”
Doc. 248 at 105. Ozuligbo performed the tests and recorded the
results.
       Medical records introduced at trial showed that even when
patients tested negative for allergies, Ifediba prescribed immuno-
therapy, and Ozuligbo distributed it to patients. Ozuligbo filled out
patient files noting that she gave those patients the immunother-
apy injections that Ifediba had prescribed. Once, she added a note
to a patient’s file that the patient’s symptoms had improved after
immunotherapy when, in fact, the patient had tested negative for
allergies and had not received immunotherapy at all.

3
    “Doc.” numbers refer to the district court’s docket entries.
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8                       Opinion of the Court                 20-13218

       Other patients also failed to receive the immunotherapy
treatment their insurers paid for. For example, a CCMC employee
told one patient who had tested negative for allergies to come to
the clinic to receive his allergy shot. He refused to get the shot and
told CCMC not to bill his insurance for it. CCMC nonetheless
billed his insurer $2,660 for allergy treatment. And when investiga-
tors executed a search warrant on CCMC, it found under a table a
big box of “unopened and unused” vials of allergy immunotherapy
medicine, apparently discarded. Id. at 133.
       Insurer Blue Cross Blue Shield of Alabama (“BCBS”) noticed
the unusually high volume of allergy-related claims coming from
CCMC and announced that it would audit the clinic. In preparation
for the audit, Ifediba told clinic staff, including Ozuligbo, to change
patient records, turning negative allergy test results to positive and
marking allergy symptoms on the patient questionnaires. Yet BCBS
managed to uncover the fact that patients had not needed the al-
lergy tests or treatment. It requested a refund of about $220,000 in
benefits paid to CCMC for allergy services. It also informed the
Federal Bureau of Investigation (“FBI”) that CCMC could be com-
mitting health care fraud. Because the government was already in-
vestigating Ifediba’s controlled-substance prescription practices,
the FBI joined the DEA’s existing investigation.
       Agents searched CCMC’s premises and, on the same day,
interviewed Ozuligbo at her home. By that time, she had stopped
working at the clinic. Ozuligbo initially answered the agents’ ques-
tions about her work at CCMC. But when they brought out patient
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20-13218               Opinion of the Court                        9

records showing that she had logged immunotherapy injections for
patients who had tested negative for allergies, she refused to speak
further.
       A grand jury indicted Ifediba and Uchenna, charging them
with multiple counts of unlawfully distributing controlled sub-
stances outside the course of professional practice and for no legit-
imate medical purpose. They were also indicted for conspiracy to
distribute the controlled substances and for using and maintaining
CCMC for the purpose of distributing controlled substances. All
these charges concerned the prescribing of pain-management sub-
stances.
       The indictment also charged Ifediba, Uchenna, Ozuligbo,
and Ebio with conspiracy to commit health care fraud through the
allergy fraud scheme and substantive counts of health care fraud
based on the records of specific patients. It further charged that
Ifediba, Uchenna, and Ozuligbo laundered the proceeds of the ille-
gal scheme. Uchenna, who had suffered a severe stroke, was dis-
missed from the case as incompetent. Ebio pled guilty to one count
of conspiracy to commit health care fraud and agreed to testify
against Ifediba and Ozuligbo.
       Before trial, the government filed three motions in limine to
exclude evidence that Ifediba and Ozuligbo planned to present.
Two motions sought to exclude evidence of Ifediba’s “good
care”—legitimate medical treatment that he had provided to some
patients. The third motion sought to exclude Ozuligbo’s evidence
of Nigerian cultural norms requiring her to obey her older brother.
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10                        Opinion of the Court                    20-13218

Over the defendants’ opposition, the district court granted the gov-
ernments’ motions, concluding that Ifediba’s good-care evidence
was improper character evidence in that he sought to establish his
innocence by showing that he acted lawfully on some occasions.
The court also ruled that Ozuligbo’s cultural defense was irrelevant
and failed to establish duress.
B.     The Jury Heard Evidence of Health Care Fraud.
      The trial featured testimony from former CCMC patients,
undercover law enforcement officers who had posed as patients,
CCMC staff, insurance fraud investigators, medical experts, and co-
conspirator Ebio.4 The government also presented patient records
to prove health care fraud: allergy questionnaires where the patient
indicated no allergy symptoms, allergy tests showing negative re-
sults, prescriptions for immunotherapy for patients with negative
results, immunotherapy treatment logs for those same patients,
and bills to the patients’ insurers. These records were the main sup-
port for four of the health care fraud counts. The patients whose
fraudulent treatment was the subject of those counts did not tes-
tify. Instead, Special Agent P.J. Bullock, an FBI investigator, testi-
fied about their medical records. Fraud investigators for the

4
 Because the appellants raise no challenge to the sufficiency of the evidence
supporting their convictions for controlled-substances offenses, we will not
discuss the evidence supporting those offenses in detail.
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20-13218                  Opinion of the Court                              11

insurers confirmed that the insurers received the allergy claims in
question.

        Bullock testified about Patient B.B., 5 who indicated on the
clinic’s allergy questionnaire that he thought he suffered from al-
lergies. He signed an allergy test consent form, which Ifediba
signed as well, and was tested. The test came back negative, but
B.B. received a prescription for immunotherapy, signed by Ifediba,
anyway. B.B.’s allergy therapy log showed that Ozuligbo gave him
an immunotherapy injection. Bullock testified that CCMC billed
Medicare $525 for the allergy test and $2,660 for the allergy injec-
tion.
        Patient D.C.’s records were much the same. They showed
that Ifediba signed D.C.’s allergy testing consent form. Her allergy
test came back negative. Yet Ifediba prescribed her immunother-
apy. Her records show that she received five injections, three of
which were administered by Ozuligbo. According to Bullock,
CCMC billed Medicare $525 for the allergy test and $2,660 for the
allergy injections.
       The allergy questionnaire of Patient R.C. indicated that he
did not believe he suffered from allergies. Uchenna signed his al-
lergy test consent form, ordered his allergy test, and signed his

5
  To protect the patients’ privacy, the indictment referred to them by their
initials, and we follow its lead. See United States v. Pon, 963 F.3d 1207, 1215
n.5 (11th Cir. 2020).
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12                      Opinion of the Court                  20-13218

prescription for immunotherapy. Bullock testified that Uchenna
and Ifediba together billed R.C.’s private insurer a total of $525 for
an allergy test and $2,660 for immunotherapy treatment.
        Patient V.T.’s records told a different, but equally disturb-
ing, story. Her insurer received no bill for an allergy test. The in-
vestigation revealed no prescription for immunotherapy and no al-
lergy therapy log showing injections. Records documenting a Feb-
ruary visit to CCMC lacked any information about V.T. at that
visit: no vital signs, assessments, or medical plan. Yet CCMC billed
V.T.’s private insurer $2,850 for allergy treatment at this visit. Bull-
ock testified, “They billed the expensive immunotherapy, but
[there was] no record of any tests and no billing of actual tests being
conducted, just the medication.” Doc. 248 at 163.
        The government’s medical expert, Dr. Jim Christensen, told
the jury that it was “[a]bsolutely not” appropriate to test patients
for allergies just because their health insurance would pay for the
test. Doc. 250 at 94. The defense team’s medical expert agreed.
Christensen further testified that it was inappropriate to prescribe
immunotherapy to someone who had tested negative for allergies:
“A board-certified allergist will not prescribe when the tests are
negative.” Id. at 122.
C.     A Juror Misconduct Issue Arose.
      At the close of the government’s evidence, both defendants
moved for a judgment of acquittal, which the court denied. At that
time, the district court learned of an issue with a juror. A
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20-13218                 Opinion of the Court                          13

“concerned citizen” had sent an email to the clerk’s office inform-
ing the court that a juror had been “discussing the case in some
detail with people she works with” and, contrary to the court’s in-
structions, had “googled the case.” Doc. 252 at 212–13. After dis-
cussing the matter with the parties, the court decided that it needed
to identify the juror, “talk to her, and see if this is self-contained, if
there’s been some violation of [the court’s] instructions.” Id. at 214.
       The next day, the court determined that the citizen’s email
was credible because it contained information that could only have
come from someone with access to trial evidence. Having followed
up with the tipster, the court identified the juror as one of the al-
ternates. The court and the parties discussed different approaches
for handling the matter. All agreed that, as an alternate, the juror
should be dismissed and that, before dismissing her, the court
should question her about whether she had shared any information
from her independent research with other jurors. The parties
agreed to the court’s plan—to dismiss the alternate by telling her
that she was no longer needed as an alternate juror and, without
mentioning the email, ask her “routine” “due diligence” questions
about sharing outside information with other jurors. Doc. 253 at 6,
7. The attorneys would be allowed to request a sidebar during the
questioning and pose new questions as desired.
       The court, with the parties present, brought in the alternate
juror and asked her if she was “aware of any incident of jurors de-
liberating about the case or doing any investigation beyond the ev-
idence in this case.” Id. at 12. She said she was not aware of any
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14                     Opinion of the Court                 20-13218

such incident. When the court asked the parties if they had any
other questions for her, they said no, declining the opportunity for
a sidebar.
        After dismissing the alternate, the court asked the defend-
ants if they were satisfied. Ifediba’s counsel was “satisfied with the
questioning” but nevertheless moved for a mistrial. Doc. 253 at 16.
He contended that, because the alternate had been dishonest about
having independently researched the case, it was “difficult to be-
lieve” that she had not shared her research with other jurors. Id.
He said that “[T]here is a perception that my client cannot get a fair
trial at this point.” Id. The court, noting the lack of “positive evi-
dence” that the alternate had discussed her research with the other
jurors, decided that there was no basis for a mistrial on such “scant
information” that other jurors had received any extrinsic infor-
mation or done anything improper. Id. at 18, 21. It denied the mo-
tion.
        Counsel for Ozuligbo suggested that the court “inquire of
the present jurors . . . whether or not there ha[d] been any discus-
sions about any sort of outside information,” and Ifediba’s counsel
urged that the court question the jurors “one by one.” Id. at 21, 26.
The court accepted Ozuligbo’s counsel’s suggestion and declined
Ifediba’s counsel’s, explaining that it was unnecessary to take the
“fairly extraordinary” step of individual questioning to address the
“metaphysical possibility” that the alternate juror had tainted the
other jurors. Id. at 30. The court was reluctant to “start a witch
hunt” by “call[ing] out jurors one on one and accus[ing] them of”
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20-13218                Opinion of the Court                         15

improperly discussing the case. Id. at 33. Individual questioning,
the court reasoned, was unlikely to “get[] to the truth.” Id. at 33,
35. The court decided instead to address the jurors collectively.
        The court announced its plan: to instruct the jurors that they
must base their verdict only on “the evidence presented in the
courtroom and the instructions given by the Court,” remind them
that the defendants are presumed innocent until all the evidence is
in, ask them to stand to affirm that they understand the instruction
and will comply, and encourage them to tell the courtroom deputy
if they knew of any violation of the instructions. Doc. 253 at 38–39.
The court considered self-reporting to the deputy to be more likely
to yield results because the deputy “ha[d] a relationship with each
one of them.” Id. at 35. The defendants did not object.
       Once the jury returned to the courtroom, the court framed
the instructions as a reminder conveniently provided at the mid-
point of the trial. It instructed the jury collectively according to the
plan laid out to the parties:
       First, I want you to understand that your verdict in
       this case must be based solely on the evidence pre-
       sented in the courtroom and the instructions I give
       you. You are to give a full presumption of innocence
       to both defendants until you’ve heard all the evi-
       dence. They are presumed innocent until you begin
       your deliberations finally, after receiving my final in-
       structions. You’re not to do any type of research or
       investigation or any deliberations until you receive all
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16                     Opinion of the Court                 20-13218

       the evidence and you’re all together collectively to do
       so.
       Everyone understand this instruction? Okay. I’m ask-
       ing you to reconfirm that. I expect that if there’s a
       problem with any juror following this instruction,
       that one of you with awareness of that will let [the
       courtroom deputy] know immediately of any viola-
       tion of this instruction. Everyone understand that?
       That’s each of you have a duty to do that.
       If you’re willing to follow my instruction in each of
       these respects, please stand.
Id. at 41–42. Each juror stood to signal willingness to follow the
instructions. The trial concluded without any report of jurors vio-
lating the court’s instructions.
D.     The Court Convicted and Sentenced the Defendants.
      At the close of evidence, Ifediba renewed his motion for
judgment of acquittal, which the court denied. The court also de-
nied Ozuligbo’s renewed motion for judgment of acquittal.
       The jury returned guilty verdicts for Ifediba and Ozuligbo.
As relevant to this appeal, the jury convicted Ifediba of conspiracy
to commit health care fraud, in violation of 18 U.S.C. § 1349, and
substantive health care fraud, in violation of 18 U.S.C. § 1347. It
also convicted him of conspiracy to distribute or dispense con-
trolled substances outside the course of professional practice, in vi-
olation of 21 U.S.C. § 846, and substantive counts of unlawfully dis-
tributing or dispensing the controlled substances, in violation of
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20-13218                  Opinion of the Court                             17

21 U.S.C. § 841(a)(1), as well as maintaining CCMC for unlawful
distribution of controlled substances, in violation of 21 U.S.C.
§ 856.
        The jury convicted Ozuligbo of conspiracy to commit health
care fraud and substantive health care fraud. Ifediba and Ozuligbo
were also found guilty of money laundering the proceeds of the
illegal allergy scheme and conspiring to commit that crime.
     The court sentenced Ifediba to 360 months of imprisonment
and Ozuligbo to 36 months.
       To determine Ifediba’s sentence, the presentence investiga-
tion report (“PSR”) set the base offense level for the controlled sub-
stances conspiracy at 36. Following § 2D1.1(c)(2) of the Sentencing
Guidelines, the PSR calculated the quantity of illegal substances for
which Ifediba was responsible, estimating the converted drug
weight to be between 30,000 and 90,000 kilograms. This estimate
came from an analysis of Alabama’s Prescription Drug Monitoring
Program (“PDMP”) data spanning the charged conspiracy period
from May 2013 to January 2016. 6 Ifediba objected to the PSR’s drug
quantity calculation.

6
 The PDMP is a database that tracks all controlled substances prescribed to a
patient in a state. United States v. Akwuba, 7 F.4th 1299, 1305 n.2 (11th Cir.
2021). It lists the type of controlled substance, the amount of the substance
prescribed, and the name of the doctor who prescribed it. PDMP data is com-
monly used in pill mill cases like this one. See, e.g., id. at 1305, 1309–10.
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18                     Opinion of the Court                20-13218

       Only Ifediba challenges the sentence imposed. At his sen-
tencing hearings, held over the course of two days, Ifediba argued
that the court should derive the drug quantity using only the pre-
scriptions admitted into evidence at trial that the jury found to be
unlawful. The drug quantity for these prescriptions totaled be-
tween 1,000 and 3,000 kilograms, which would lead to a base of-
fense level of 30 under the guidelines. Ifediba contended that the
court should not extrapolate from the prescriptions evaluated by
the jury to assume that all the controlled substances prescribed dur-
ing the conspiracy period were prescribed unlawfully.
        The government presented an expert witness from the
DEA, Paul Short, to elaborate on his trial testimony regarding the
PDMP records of CCMC patients. His analysis showed that Ifediba
and Uchenna had prescribed 1,761 kilograms of converted drug
weight to the 21 patients whose prescriptions the jury had found
unlawful. Short also looked beyond those patients to the 1,850 pa-
tients to whom Ifediba alone had prescribed controlled substances
during the two-and-a-half-year-long conspiracy. His analysis re-
vealed that 96% of those patients had been prescribed at least one
opioid. The PDMP data also indicated that Ifediba had prescribed
the controlled-substances equivalent of 85,264 kilograms of con-
verted drug weight. The government argued that the larger num-
ber required a base offense level of 36 under § 2D1.1(c)(2). The
court agreed. After applying sentencing enhancements and using
Ifediba’s criminal history score of I, the district court calculated
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20-13218                Opinion of the Court                        19

Ifediba’s guidelines range as 360 months of imprisonment to im-
prisonment for life. The court sentenced Ifediba to 360 months.
       Ifediba and Ozuligbo timely filed this appeal. Ifediba appeals
the court’s refusal to grant a mistrial and its decision to address the
alternate juror’s misconduct by instructing the jury collectively in-
stead of questioning them individually. He also challenges the ex-
clusion of his good-care evidence, the sufficiency of the evidence
upholding his conviction on four counts of health care fraud, and
his sentence. Ozuligbo challenges the exclusion of her cultural-de-
fense evidence and the sufficiency of the evidence supporting her
conviction for conspiracy to commit health care fraud.
                II.    STANDARDS OF REVIEW
       We generally review a district court’s evidentiary rulings for
an abuse of discretion. United States v. Sarras, 575 F.3d 1191, 1209
n.24 (11th Cir. 2009). Whether the exclusion of the evidence vio-
lated a constitutional guarantee is a legal question that we review
de novo. Id.
       We review for an abuse of discretion a court’s procedure for
investigating juror misconduct. United States v. Harris, 908 F.2d
728, 733 (11th Cir. 1990). Similarly, we review the denial of a mo-
tion for a mistrial for an abuse of discretion. United States v. Green,
981 F.3d 945, 959 (11th Cir. 2020).
      “We review de novo a challenge to the denial of a Rule 29
motion for a judgment of acquittal based on sufficiency of the evi-
dence grounds.” United States v. Gonzalez, 834 F.3d 1206, 1214
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20                     Opinion of the Court                  20-13218

(11th Cir. 2016). We must review the evidence in the light most
favorable to the jury’s verdict and draw all inferences in its favor.
Id.
       A district court’s determination of drug quantity is reviewed
for clear error. United States v. Reeves, 742 F.3d 487, 506 (11th Cir.
2014).
                         III.      ANALYSIS
       We first discuss the district court’s evidentiary rulings ex-
cluding Ifediba’s good care evidence of proper medical treatment
and Ozuligbo’s cultural-defense evidence that Nigerian cultural
norms required her to obey Ifediba as her older brother. Second,
we examine the court’s choice to address one juror’s misconduct
by collectively instructing the jury. Third, we review the trial evi-
dence to determine whether it was sufficient to support Ifediba’s
convictions on four counts of substantive health care fraud and
Ozuligbo’s conviction for conspiracy to commit health care fraud.
Fourth, and finally, we take up Ifediba’s challenge to the drug-
quantity calculation that the court used to sentence him.
A.     The Court Properly Excluded Defense Evidence of Good
       Care and Cultural Norms.
       Ifediba and Ozuligbo each challenge the district court’s ex-
clusion of certain evidence at trial.
       The district court excluded Ifediba’s good-care evidence
showing that he provided legitimate medical treatment to some
patients. The court determined that this was merely an attempt to
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20-13218               Opinion of the Court                        21

portray Ifediba as a person of good character by pointing to his
prior good acts. Federal Rule of Evidence 404(a)(1) forbids such use
of character evidence, and our precedent holds that “[e]vidence of
good conduct is not admissible to negate criminal intent.” United
States v. Camejo, 929 F.2d 610, 613 (11th Cir. 1991). The district
court did not abuse its discretion when it excluded the good-care
evidence as inadmissible character evidence. See id.
        Ifediba argues that the exclusion violated his constitutional
right to present a complete defense to the charge of unlawful dis-
tribution of controlled substances. See United States v. Hurn,
368 F.3d 1359, 1362–63 (11th Cir. 2004). According to Ifediba, the
court should have admitted the good-care evidence because it
“tend[ed] to place the story presented by the prosecution in a sig-
nificantly different light, such that a reasonable jury might receive
it differently.” Id. at 1363. But the government never alleged that
Ifediba unlawfully treated every patient who walked through
CCMC’s doors; indeed, it conceded that his treatment of some pa-
tients was legitimate. Thus, it was no defense that Ifediba lawfully
treated some patients. The district court did not abuse its discretion
by excluding such evidence as improper character evidence, and
the exclusion did not violate Ifediba’s constitutional right to pre-
sent a defense.
       Ozuligbo challenges the district court’s exclusion of evi-
dence supporting a defense to voluntary participation in the con-
spiracy based on the Nigerian cultural norms requiring her to be
“subservient” to her older brother. Doc. 86 at 3. The district court
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22                      Opinion of the Court                 20-13218

did not abuse its discretion in excluding this evidence from trial.
We have rejected a similar argument before. See United States v.
Almanzar, 634 F.3d 1214, 1223 (11th Cir. 2011). In Almanzar, a dis-
trict court set aside the jury’s guilty verdict because “cultural ex-
pectations” required the defendant to obey her male family mem-
bers. Id. at 1221. Seeing error in the court’s reliance on stereotypes,
among other things, we vacated the judgment of acquittal and di-
rected the court to reinstate the jury’s verdict. Id. at 1223–24. Ozu-
ligbo’s argument here is no different, and we reject it.
B.     The Court Acted Within Its Discretion in Addressing Juror
       Misconduct by Instructing the Jury Collectively.
        When an allegation of juror misconduct arises, the court
must determine whether the misconduct occurred and whether it
was prejudicial. Harris, 908 F.2d at 733. But there is no bright-line
rule requiring a district court “to investigate the internal workings
of the jury whenever a defendant asserts juror misconduct.” United
States v. Cuthel, 903 F.2d 1381, 1382–83 (11th Cir. 1990). A district
court has “broad discretion in deciding whether to interrogate ju-
rors regarding alleged misconduct.” United States v. Barshov,
733 F.2d 842, 850 (11th Cir. 1984). “[T]he investigative procedure
to be used in checking for juror misconduct falls within the discre-
tion of the district court.” United States v. Caldwell, 776 F.2d 989,
997 (11th Cir. 1985). A court abuses its discretion and commits re-
versible error when it fails to investigate as thoroughly as the situ-
ation requires and the insufficient investigation prejudices the de-
fendant. See id. at 1000; Harris, 908 F.2d at 733.
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20-13218               Opinion of the Court                       23

       We evaluate the court’s chosen investigative procedure
based on where the juror misconduct falls along a “continuum fo-
cusing on two factors.” Caldwell, 776 F.2d at 998. “At one end of
the spectrum the cases focus on the certainty that some impropri-
ety has occurred.” Id. “The more speculative or unsubstantiated
the allegation of misconduct, the less the burden to investigate.”
Id. “At the other end of the continuum lies the seriousness of the
accusation.” Id. “The more serious the potential jury contamina-
tion, especially where alleged extrinsic influence is involved, the
heavier the burden to investigate.” Id. When a party makes a “col-
orable showing of extrinsic influence,” the court must investigate
to determine whether the influence was prejudicial. Barshov,
733 F.2d at 851. But “[t]he duty to investigate arises only when the
party alleging misconduct makes an adequate showing of extrinsic
influence to overcome the presumption of jury impartiality.” Id.
       At the more speculative end of the spectrum lies Barshov, a
case in which a juror’s son had spent time talking to the jurors dur-
ing recesses and eating lunch with them. Id. The son had also spo-
ken to defense counsel, the defendant’s wife, and the prosecutor
about the case. Id. After the jury returned a guilty verdict, defense
counsel asked the court to interview each juror individually be-
cause of defense counsel’s “suspicion” that the son had improperly
influenced the jury with “extraneous, prejudicial information.” Id.
(internal quotation marks omitted). But counsel failed to support
that suspicion with any evidence indicating “the improper convey-
ance of information to the jury.” Id. at 852 (internal quotation
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24                        Opinion of the Court                      20-13218

marks omitted). The district court denied the motion, and we af-
firmed. Id. at 851. Because the defense failed to show—beyond
speculation—that the son had “improper discussions” with the ju-
rors or that his conduct “impugned in any way the integrity of the
trial process,” we held that the district court acted within its discre-
tion in declining to interview each juror individually. Id. at 852.
       At the other end of the spectrum, reflecting substantiated
and serious outside influence, is an outside party’s attempt to influ-
ence a juror, as seen in United States v. Forrest, 620 F.2d 446, 456–
57 (5th Cir. 1980). 7 There, a husband and wife were convicted of
federal crimes related to receiving stolen property. Id. at 449. A ju-
ror’s niece, a friend of one of the defendants, tried to persuade the
juror to vote for acquittal. Id. at 456. The court excused the juror
but allowed the trial to continue, and it ended with both defendants
being convicted. Id. at 449, 457. On appeal, the husband argued that
as a result of the outside influence, he did not receive a trial by a
fair and impartial jury. Id. at 456. Noting that “[a]ny off-the-record
contact with a jury is presumptively prejudicial,” we determined
that the government had failed to carry its burden of proving that
“such a contact did not affect the jury.” Id. at 457. Although the
dismissed juror reported that the other jurors had no knowledge of
the contact, her testimony was “insufficient” due to the seriousness

7
 In Bonner v. City of Prichard, 661 F.2d 1206, 1209 (11th Cir. 1981) (en banc),
we adopted as binding all Fifth Circuit precedent handed down prior to Octo-
ber 1, 1981.
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20-13218               Opinion of the Court                        25

of the misconduct as “[c]ontacts such as those that may have oc-
curred in this case raise serious questions of prejudice.” Id. at 457–
58. We observed that “[o]nly the other jurors [could] enlighten us”
as to whether the dismissed juror had spoken to them about the
case. Id. at 457. We remanded the case so the court could question
the jurors individually to determine whether the dismissed juror
had discussed the case with them and shared “extraneous prejudi-
cial material.” Id. at 458.
       Somewhere in the middle of spectrum, illustrating a some-
what substantiated and relatively serious allegation, sits United
States v. Brantley, 733 F.2d 1429 (11th Cir. 1984). In Brantley, after
the jury returned guilty verdicts, one juror (Miller) told the court
that, during deliberations, another juror (Blige) had “brought into
the jury room the extrinsic fact that [a defendant] had been in-
volved with drug smuggling before.” Id. at 1439. At a hearing, Blige
denied making the remark, and the court prevented defense coun-
sel from questioning Miller or the other jurors. Id. Observing that
Miller’s “personal knowledge” lent credibility to her allegation, we
held that the court’s refusal to investigate it further was an abuse
of discretion and remanded the case so the court could uncover
whether the incident occurred and, if it did, whether there was a
reasonable possibility of prejudice to the defendant. Id. at 1440–41.
      Here, the court received a credible tip that the alternate ju-
ror had “googled the case” and discussed it with her coworkers.
Doc. 252 at 212–13. When the court asked her if she was aware of
any jurors independently researching the case or discussing it, she
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26                     Opinion of the Court                20-13218

said no. The court dismissed the alternate. Even though the court
had questioned the alternate according to the plan agreed upon by
the parties, Ifediba moved for a mistrial, arguing that the alternate
might have discussed her research with the other jurors. Though
the tip did not say that the alternate had shared information with
other jurors, Ifediba urged the court to ask each juror individually
about participation in any discussions of outside information. Re-
fusing to embark on a “witch hunt,” the court instead chose to ad-
dress the jurors collectively, reminding them of the court’s instruc-
tions and asking them to report any improper discussions to the
courtroom deputy. Doc. 253 at 33.
       This incident falls at the less serious end of the spectrum of
juror misconduct. To be sure, the alternate ignored the court’s in-
structions to refrain from researching the case online or elsewhere.
The tip that she had done so was substantiated given that the tip-
ster knew details that could only have come from the trial. And
outside research by a juror is prohibited because “[t]he sixth
amendment guarantee of a trial by jury requires the jury verdict to
be based on the evidence produced at trial.” United States v. Per-
kins, 748 F.2d 1519, 1533 (11th Cir. 1984). The court appropriately
dealt with the substantiated instance of misconduct by dismissing
the alternate, thereby preventing her from playing any role in the
verdict. Significantly, Ifediba’s counsel agreed to the court’s pro-
posed method of questioning the alternate and declined the oppor-
tunity to request a sidebar during her questioning or ask further
questions.
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20-13218               Opinion of the Court                        27

       Ifediba’s charge of further misconduct, however, was purely
speculative. There was no evidence that the tainted alternate had
improper discussions with the rest of the panel. Ifediba’s suspicion
arose because, in response to the court’s questioning, the alternate
denied that she had violated the court’s instructions. Her lack of
candor caused Ifediba to posit that she had committed more seri-
ous misconduct by sharing outside information with the other ju-
rors. Unlike the alleged improper discussions in Brantley, Ifediba’s
allegation was based not on personal knowledge, but on the “met-
aphysical possibility that [the alternate] may have discussed some-
thing” with other jurors. Doc. 253 at 25; Brantley, 733 F.2d at 1439.
Because he presented no evidence to support his suspicion, it re-
mained “mere speculation” and nothing more. Barshov, 733 F.2d
at 851. Thus, just like in Barshov, the trial court had discretion to
refrain from taking the extraordinary step of individually question-
ing the jurors to address the allegation of misconduct.
        Even so, the court took the additional step of instructing the
remaining jurors collectively and obtaining their agreement to fol-
low the court’s instructions and report any violation of the instruc-
tions. See Harris, 908 F.2d at 734 (“The district court cured any pos-
sible taint by questioning the jurors on their ability to remain im-
partial and giving them an admonition to keep an open mind.”).
Given its speculative nature, the allegation of improper jury discus-
sions did not require a more intensive investigation than the district
court performed.
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28                         Opinion of the Court                        20-13218

       But even if the court should have questioned the jurors indi-
vidually, Ifediba failed to show any prejudice to his defense or lack
of integrity in the trial process. 8 See Harris, 908 F.2d at 733; Bar-
shov, 733 F.2d at 852 (“In the absence of a colorable showing that
the conduct complained of impugned in any way the integrity of
the trial process, the district court was not required to make further
inquiries or to conduct a hearing, and its refusal to do so did not
constitute an abuse of discretion.”).
        Before concluding our discussion of this issue, we note our
agreement with the district court that individual questioning of the
jury is not to be undertaken lightly. It has the potential to “aggra-
vate the situation” by drawing attention to misconduct. Barshov,
733 F.2d at 850 (internal quotation marks omitted). The district
court in United States v. Caldwell declined to question a juror who
had spoken with another juror accused of misconduct. Caldwell,
776 F.2d at 995. We found no abuse of discretion, recognizing the
court’s concern that “direct inquiry of any of the jurors by counsel
might itself contaminate the jury panel.” Id. The district court here

8
  In his brief, Ifediba failed to support with arguments and citations to author-
ity his challenge to the district court’s denial of a mistrial. Thus, we deem this
issue abandoned. See Sapuppo v. Allstate Floridian Ins. Co., 739 F.3d 678, 681
(11th Cir. 2014). Were we to reach the merits, though, we would affirm the
district court. “A defendant must show substantial prejudice to be granted a
mistrial.” United States v. Barsoum, 763 F.3d 1321, 1340 (11th Cir. 2014).
Ifediba has failed to show any prejudice; therefore, we find no abuse of discre-
tion in the district court’s denial of his mistrial motion.
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20-13218                   Opinion of the Court                              29

shared that concern, warning counsel that “if we start questioning
each juror one on one, they will believe we’re accusing them.”
Doc. 253 at 33. Rather than risk “unintended consequences,” the
court made the reasoned decision to investigate the speculative al-
legation by addressing the jurors collectively and encouraging
them to self-report any improper discussions to the courtroom dep-
uty. 9 Id.; see Harris, 908 F.2d at 734 (“[T]he district court’s limited
hearing on the matter was appropriate because additional investi-
gation might have over-emphasized the remark.”).
       To sum up, we see no abuse of discretion in the district
court’s handling of the juror misconduct. After all, “[t]he whole
point of discretion is that there is [a] range of options open, which
means more than one choice is permissible.” United States v.
Dominguez, 226 F.3d 1235, 1247 (11th Cir. 2000). And we recog-
nize that the district court has the “superior vantage point” from
which to evaluate juror misconduct. Caldwell, 776. F.2d at 999.
“The district court is in the best position to make the necessary de-
terminations. Having clothed the court with broad discretion, we
will not now attempt to second-guess the evaluation and ultimate

9
 The court had good reason to believe that the jurors would inform the court-
room deputy of any violations of the court’s instructions. Earlier in the trial,
individual jurors had approached the deputy and self-reported concerns about
potential impropriety: a juror who worked at the post office had met someone
named “Ebio” at work, another juror recognized a witness from church, and
a third juror realized that CCMC was located across the street from a family
member’s office.
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30                     Opinion of the Court                 20-13218

holding.” Barshov, 733 F.2d at 851. We see no abuse of discretion
here.
C.    Sufficient Evidence Supported Ifediba and Ozuligbo’s Con-
      victions.
       Sufficiency-of-the-evidence review requires us to examine
“whether the evidence, when viewed in the light most favorable to
the government, and accepting reasonable inferences and credibil-
ity choices by the fact-finder, would enable the trier of fact to find
the defendant guilty beyond a reasonable doubt.” United States v.
Monroe, 866 F.2d 1357, 1365 (11th Cir. 1989). We will affirm a con-
viction unless there is “no reasonable construction of the evidence”
from which the jury could have found the defendant guilty beyond
a reasonable doubt. United States v. Garcia, 405 F.3d 1260, 1269
(11th Cir. 2005).
      1. Patient Records Were Sufficient to Support Ifediba’s
         Convictions for Substantive Health Care Fraud.
       The jury convicted Ifediba of 10 counts of substantive health
care fraud, in violation of 18 U.S.C. § 1347(a). The statute provides:
      Whoever knowingly and willfully executes, or at-
      tempts to execute, a scheme or artifice—
      (1)   to defraud any health care benefit program; or
      (2)   to obtain, by means of false or fraudulent pre-
            tenses, representations, or promises, any of the
            money or property owned by, or under the
            custody or control of, any health care benefit
            program,
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20-13218               Opinion of the Court                       31

      in connection with the delivery of or payment for
      health care benefits, items, or services, shall be fined
      under this title or imprisoned not more than 10 years,
      or both.
18 U.S.C. § 1347(a). Thus, to be convicted “in a health care fraud
case, the defendant must be shown to have known that the claims
submitted were, in fact, false.” United States v. Medina, 485 F.3d
1291, 1297 (11th Cir. 2007). “A person makes a false claim if the
treatments that were billed were not medically necessary or were
not delivered to the patients.” United States v. Chalker, 966 F.3d
1177, 1188 (11th Cir. 2020) (internal quotation marks omitted).
        Ifediba challenges the sufficiency of the evidence supporting
4 of his 10 convictions for health care fraud. Each conviction arose
from his or co-conspirator Uchenna’s treatment of a particular pa-
tient, six of whom testified at trial. Ifediba challenges the convic-
tions stemming from the treatment of the four patients who did
not testify. He argues, without citation to authority, that documen-
tary evidence alone was insufficient to establish health care fraud
and that the government needed to present patient testimony to
prove its case. But we reject his argument because documentary
evidence and testimony from other witnesses sufficiently estab-
lished that he knowingly made false representations to health care
benefits providers to obtain money from health care benefit pro-
grams.
       For each of the counts Ifediba challenges, patient files and
billing records demonstrated that he or his co-conspirator,
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32                         Opinion of the Court                       20-13218

Uchenna, ordered treatment knowing that it was medically unnec-
essary. The jury heard that Ifediba ordered allergy tests for Patient
B.B. and Patient D.C. According to their patient files, both patients
tested negative for allergies, yet Ifediba prescribed them immuno-
therapy anyway. Patient R.C.’s allergy test was ordered by
Uchenna, who prescribed immunotherapy despite a negative test
result. 10 Patient V.T. received neither an allergy test nor an immu-
notherapy prescription, but her insurer received a bill for immuno-
therapy treatment from CCMC. These patients did not have aller-
gies. Ifediba knew they did not have allergies because the tests that
CCMC performed came back negative. Although the patients did
not need what he prescribed, he nevertheless made fraudulent rep-
resentations to the insurers that the patients needed allergy treat-
ment. It is true that none of the four patients testified to that effect,
but other witnesses did.
      Testimonial evidence confirmed that Ifediba likely knew the
treatment was unnecessary but billed insurers for it anyway. The

10
   Though Uchenna, not Ifediba, ordered the test and prescribed the medica-
tion for Patient R.C., the false claim provides support for Ifediba’s conviction
nonetheless. Ifediba does not challenge his conviction for conspiracy to com-
mit health care fraud, and, as a co-conspirator, he is liable for the reasonably
foreseeable crimes that his co-conspirators committed in furtherance of the
conspiracy. Chalker, 966 F.3d at 1189 (citing Pinkerton v. United States,
328 U.S. 640 (1946)). The fact that CCMC, through Ifediba himself or his wife,
“would submit fraudulent claims as a consequence and in furtherance of this
conspiracy is virtually the definition of ‘reasonably foreseeable.’” Id. at 1189–
90 (internal quotation marks and emphasis omitted).
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20-13218               Opinion of the Court                       33

government’s medical expert, Dr. Jim Christensen, testified that it
was “inappropriate” to prescribe immunotherapy to someone who
tested negative for allergies. Doc. 250 at 99. This suggests that
Ifediba knew that the allergy treatment was medically unnecessary,
and the claims he submitted thus were false. Special Agent Bullock
testified that Ifediba billed insurers $525 for an allergy test and
$2,660 or $2,850 for immunotherapy. The testimony of fraud in-
vestigators for the insurers confirmed that CCMC submitted al-
lergy-related claims for these patients. Further testimony showed
that Ifediba personally signed all the bills charging Medicare and
private insurers for the medically unnecessary treatment, thereby
defrauding them through false claims.
        The paper trail and testimony illustrating Ifediba’s fraudu-
lent representations are enough for a jury; live testimony from pa-
tients, while helpful, is not required. “[A] defendant’s knowledge
can be proven in more than one way.” United States v. Clay,
832 F.3d 1259, 1311 (11th Cir. 2016). Nothing in our precedent re-
quires that patients testify regarding the defendant’s fraudulent
representations to insurers to support a health care fraud convic-
tion. See generally id. at 1294–1304, 1311 (upholding convictions
for health care fraud based on Medicaid expense reports unsup-
ported by patient testimony). And in this case, there was also testi-
mony—not from patients but from Christensen, Bullock, and the
insurers—supporting the healthcare fraud convictions. Evaluating
the evidence, a reasonable jury could conclude that Ifediba com-
mitted health care fraud by knowingly prescribing medically
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34                     Opinion of the Court                20-13218

unnecessary treatment and submitting false information to receive
payment from healthcare benefit programs. We thus affirm the
jury’s verdict on the four counts of health care fraud.
      2. Sufficient Evidence Supported Ozuligbo’s Conviction for
         Conspiracy to Commit Health Care Fraud.
       To sustain a conviction for conspiracy to commit health care
fraud in violation of 18 U.S.C. §§ 1347 and 1349, the government
must establish beyond a reasonable doubt that: “(1) a conspiracy
existed to commit health care fraud under 18 U.S.C. § 1347; (2) [the
defendant] knew of the conspiracy; and (3) [the defendant] know-
ingly and voluntarily joined it.” Gonzalez, 834 F.3d at 1214. Be-
cause the crime of conspiracy is “predominantly mental in compo-
sition,” the government may prove these elements by circumstan-
tial evidence and inferences therefrom. United States v. Moran,
778 F.3d 942, 960 (11th Cir. 2015) (internal quotation marks omit-
ted). The government need not prove that the defendant knew all
the details of the conspiracy; it need only prove “that the defendant
knew of the essential nature of the conspiracy.” Gonzalez, 834 F.3d
at 1215 (internal quotation marks omitted). “[A] conspiracy convic-
tion will be upheld when the circumstances surrounding a person’s
presence at the scene of conspiratorial activity are so obvious that
knowledge of its character can fairly be attributed to her.” United
States v. Mateos, 623 F.3d 1350, 1362 (11th Cir. 2010) (alterations
adopted) (internal quotation marks omitted). “The Government
can establish that a defendant voluntarily joined the conspiracy
through proof of surrounding circumstances such as acts
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20-13218               Opinion of the Court                        35

committed by the defendant which furthered the purpose of the
conspiracy.” Gonzalez, 834 F.3d at 1215 (internal quotation marks
omitted).
       There was more than sufficient evidence to demonstrate
that CCMC defrauded insurers through an allergy fraud scheme.
The only question is whether Ozuligbo was a knowing and volun-
tary participant in the conspiracy. Ozuligbo argues that the govern-
ment established neither her knowledge of the conspiracy nor her
voluntary participation in it. Rather than a co-conspirator, she as-
serts that she was “merely an employee.” Ozuligbo’s Brief at 20.
The evidence showed otherwise.
       To begin with, patient medical records illustrated that Ozu-
ligbo knew of the conspiracy to provide immunotherapy treatment
to patients who had tested negative for allergies. She gave patients
allergy tests, signing her name to the test records. She recorded the
negative results but also recorded that she administered immuno-
therapy to them. Her initials were on Patient D.C.’s allergy log list-
ing the three injections she purportedly gave this patient who
tested negative for allergies. Patient B.B.’s allergy log also showed
a negative test followed by immunotherapy treatment. For an-
other patient—who had also tested negative for allergies—she
noted that the patient said the immunotherapy was alleviating her
symptoms. But the patient testified that she never had allergies,
never received an injection, and never said that the injections were
helping her.
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36                     Opinion of the Court                20-13218

       These medical records further show that Ozuligbo partici-
pated in the conspiracy by filing paperwork for treatments that
were medically unnecessary and treatments that were not deliv-
ered to the patients. See Chalker, 966 F.3d at 1188. The evidence
that Ozuligbo filled out fraudulent paperwork supports the infer-
ence that Ozuligbo “played a daily and active role in furthering the
unlawful objectives” of the conspiracy. Gonzalez, 834 F.3d at 1217
(upholding the conviction of a defendant who filled out fraudulent
logs indicating that she gave patients medically unnecessary treat-
ment).
       Then, too, Ozuligbo was hired under unusual circum-
stances, suggesting that she was a knowing participant in the con-
spiracy. Ifediba pressured Ebio to hire her as an ASNA allergy tech-
nician even though ASNA already had enough technicians. And
Ozuligbo knew that ASNA was paying her “double the money that
[the] other technicians were making.” Doc. 251 at 175. The jury
could infer that Ozuligbo understood her special treatment to be
part of a larger scheme that gave her brother the leverage to insist
on her employment and benefits.
       Ozuligbo knew that the larger scheme included CCMC’s
practice of testing every insured patient, and her participation in
the practice shows that she knew about and participated in the con-
spiracy to commit health care fraud. Christensen, the govern-
ment’s medical expert, told the jury that it was neither medically
necessary nor appropriate to test patients for allergies based solely
on the fact that their health insurance would cover it. But this is
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20-13218                Opinion of the Court                        37

precisely what CCMC did. It had a “blanket practice” of performing
allergy tests on all insured patients after first confirming coverage
with their insurers. Doc. 247 at 195. It did not test cash-paying pa-
tients for allergies. In addition to testing the patients, Ozuligbo was
responsible for calling their insurers and confirming coverage of al-
lergy-related claims. Although confirming insurance coverage,
standing alone, could be innocent behavior, the fact “[t]hat a pur-
ported medical care clinic” performed allergy tests on every in-
sured patient who walked through its door “is, to put it charitably,
a most unusual arrangement.” Gonzalez, 834 F.3d at 1215.
       And when patients or fellow technicians objected to the un-
usual arrangement, Ozuligbo furthered the conspiracy by convinc-
ing them to go along with it despite their misgivings. Ebio testified
that “there were some patients that did not want to get tested, but
when they were referred back to either Dr. Ifediba or his sister, Jus-
tina [Ozuligbo], the patient would then accept the testing.” Doc.
251 at 96. A fellow technician, noticing that patients were being
pressured into taking the allergy tests, voiced her concerns about
the practice to Ozuligbo. Listen to Ifediba, Ozuligbo told the tech-
nician, “You just need to do what you got to do.” Doc. 250 at 151.
The jury could reasonably conclude from this evidence that Ozu-
ligbo persuaded patients and technicians to acquiesce to the medi-
cally unnecessary allergy testing because she knew about the con-
spiracy and voluntarily participated in it.
      But the evidence does not end there. Ozuligbo’s conversa-
tion with Special Agent Bullock supports an inference that she
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38                     Opinion of the Court                 20-13218

knew about the nature of the conspiracy and participated in it. Bull-
ock arranged to meet Ozuligbo at her house for an interview.
Standing in her driveway, Ozuligbo told Bullock that she per-
formed allergy tests and provided immunotherapy at CCMC when
she used to work there. She told him that CCMC “only did allergy
testing and immunotherapy for patients with insurance” because
“it was expensive and cash-paying patients wouldn’t pay for it.”
Doc. 247 at 49. Bullock showed her some positive allergy tests that
she had performed, and Ozuligbo confirmed her handwriting on
the tests. Unprompted, she told Bullock that, if the tests were neg-
ative, the patients would not get immunotherapy. Bullock showed
her a negative test, which Ozuligbo confirmed she had adminis-
tered and marked as negative. He then showed her that same pa-
tient’s therapy log indicating that Ozuligbo had given the patient
four injections of allergy medication. She said that she probably
needed an attorney. On the verge of tears, she told him, “I left there
to get away from that craziness and all the crazy patients, and now
I work for peanuts.” Id. at 58.
       From this evidence, the jury readily could have found that
Ozuligbo knowingly participated in a conspiracy to bill for medical
services that were not actually medically necessary or delivered to
the patients. The entire exchange supports an inference that Ozu-
ligbo knew she had participated in a conspiracy. She told Bullock
that CCMC did not order immunotherapy for patients who tested
negative for allergies but, when confronted with evidence that she
had done just that, backed away. The jury, looking at Ozuligbo’s
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20-13218               Opinion of the Court                        39

conduct and the circumstances at CCMC, could conclude that she
knew about and participated in the conspiracy to commit health
care fraud. Having examined the evidence that supports her con-
spiracy conviction and found it to be sufficient, we reject her chal-
lenge and affirm her conviction.
D.    Ifediba’s Sentence Was Procedurally Reasonable.
       When we review for clear error the district court’s determi-
nation of the drug quantity, we will leave the finding in place unless
it leaves us with a “definite and firm conviction that a mistake has
been committed.” United States v. Rothenberg, 610 F.3d 621, 624
(11th Cir. 2010) (internal quotation marks omitted). The govern-
ment bears the burden of establishing drug quantity by a prepon-
derance of evidence. United States v. Rodriguez, 398 F.3d 1291,
1296 (11th Cir. 2005).
       Drug distribution in the medical context requires proof that
the prescription was not for a legitimate medical purpose or that
the prescription was not made in the usual course of professional
practice. See United States v. Joseph, 709 F.3d 1082, 1102 (11th Cir.
2013). When there is no drug seizure that readily demonstrates the
scale of the offense, the district court must approximate the drug
quantity based on “fair, accurate, and conservative estimates” of
the quantity. United States v. Zapata, 139 F.3d 1355, 1359 (11th Cir.
1998); U.S. Sent’g Guidelines Manual § 2D1.1 cmt. n.5 (U.S. Sent’g
Comm’n 2018). That estimate cannot be speculative; it must be in
line with the average frequency and amount of a defendant’s drug
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40                         Opinion of the Court                        20-13218

sales over a given period. United States v. Frazier, 89 F.3d 1501,
1506 (11th Cir. 1996).
       Ifediba challenges the procedural reasonableness of his sen-
tence for conspiracy to distribute controlled substances, arguing
that the district court erred in attributing 85,264 kilograms of con-
verted drug weight to him.11 He argues that the court’s estimate of
the quantity was wrong because “[d]rug distribution in cases in-
volving physicians [is] totally different.” Ifediba’s Brief at 27. In such
cases, he contends, the court should not extrapolate from the
“cherry-picked” prescriptions found unlawful at trial but should in-
stead determine whether each prescription written by the defend-
ant was unlawful or legitimate. Doc. 242 at 32. We disagree.
       The court based its drug quantity finding on “reliable and
specific evidence”—analysis of the PDMP data of the Schedule II
controlled substances Ifediba prescribed during the conspiracy

11
   A procedurally sound sentence is substantively unreasonable if it is not jus-
tified by the totality of the circumstances and the sentencing factors set out in
18 U.S.C. § 3553(a). Gall v. United States, 552 U.S. 38, 51 (2007). The factors
require the sentencing court to consider, among other things, the nature and
circumstances of the offense, the history and characteristics of the defendant,
the kinds of sentences available, the applicable guidelines range, the pertinent
policy statements of the Sentencing Commission, the need to avoid unwar-
ranted sentence disparities among similar defendants, and the need to provide
restitution to victims. 18 U.S.C. § 3553(a)(1), (3)–(7). United States v. Trailer,
827 F.3d 933, 936 n.2 (11th Cir. 2016). Because Ifediba failed to challenge the
substantive reasonableness of his sentence, however, we consider that chal-
lenge abandoned. See Sapuppo, 739 F.3d. at 680.
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20-13218                Opinion of the Court                        41

period. United States v. Cobb, 842 F.3d 1213, 1219 (11th Cir. 2016).
The court acknowledged the possibility that some of those pre-
scriptions could have been written for a legitimate medical purpose
but concluded that the broader pill mill conspiracy to distribute
controlled substances supported an inference that most of the pre-
scriptions were unlawful. The court noted the trial evidence illus-
trating that CCMC supplied controlled substances to people who
had no medical need for them: “[W]e had evidence from witnesses
who basically said the word on the street was that if you lost your
dealer, you could go to this clinic and get what you were looking
for on the streets.” Doc. 242 at 42. Evidence also demonstrated that
Uchenna wrote her share of “bad prescriptions,” CCMC provided
an “exponentially higher amount of prescriptions” than other clin-
ics of its size, and the clinic likely engaged in unlawful drug distri-
bution before and after the conspiracy period. Doc. 331 at 12, 19.
         Similarly, in United States v. Azmat, 805 F.3d 1018, 1047
(11th Cir. 2015), we found no error in a drug-quantity estimate
based on all the prescriptions written by the defendant doctor. The
government did not have to prove that each prescription was un-
lawful because “[t]he trial evidence showed that [the clinic] was a
pill mill that did not serve a legitimate medical purpose. . . . Abun-
dant evidence showed that [the defendant] was aware of its illegit-
imacy.” Id. Here, Ifediba ran CCMC as a pill mill and was aware of
its illegitimacy. The district court did not clearly err in attributing
to him a drug quantity based on specific data from the controlled
substances he prescribed. We affirm his sentence.
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42                    Opinion of the Court                20-13218

                      IV.    CONCLUSION
     For the foregoing reasons, we affirm the district court on all
grounds.
      AFFIRMED.