find the most likely causative microbiological agent in the following 13 cases:

Case 1. One week after arriving at the Army recruit camp at Fort Ord, California, a 19-year-old recruit
becomes the first of three cases of meningitis. He has the precipitous onset of fever and headache and
feels pain in his neck when he moves his head. When he arrived at the infirmary, he had a petechial rash
on his lower extremities. On lumbar puncture, his opening pressure is slightly elevated at 22 cm H2O
(normal range is <20 cm H2O). His CSF has 1,100/mm3 white blood cells (WBCs; 80% neutrophils), 29
mg/dL glucose, and 100 mg/dL protein.
Case 2. A 60-year-old man is brought to the hospital with confusion, right-sided weakness, and fever. His
daughter reports that when she arrived at his house he thought “there were devils in the room”. On route
to the hospital, he hallucinated intermittently, saying that he smelled roses. Three days previously, he had
complained of mild nausea and vomited once. Upon arrival at the Emergency Department (ED), he has a
generalized seizure. A computed tomography (CT) scan of his head is normal, but a magnetic resonance
imaging (MRI) scan documents T1-hypointense and T2-hyperintense signals in the cortex and gray-white
matter junction in the left temporal lobe. CSF obtained by lumbar puncture contains 50 WBCs/mm3 (90%
lymphocytes) and 300 RBCs/mm3, 70 mg/dL glucose, and 100 mg/dL protein.
Case 3. A 29-year-old woman complains of an earache. She has had many
such episodes in the past, especially involving the right ear, but the most recent
episode was associated with a headache that made her nauseated. She
vomited once. After four days of those symptoms, she was driven to the hospital
because she had developed a large blind spot in her left field of vision. At the
hospital, she has a temperature of 100.6˚F (38.1˚C). A CT scan reveals a 4×3-
cm mass in her right occipital lobe, consistent with an abscess (Fig. 1 shows a thick right posterior ring enhancing lesion). A
neurosurgeon performs a needle aspiration of the abscess under CT guidance.
A smear of the aspirate reveals Gram-positive cocci and Gram-negative bacilli.
The abscess fluid is sent for culture under both aerobic and anaerobic
conditions. She is empirically treated with broad-spectrum antibiotics while
awaiting the results of the culture.
Case 4. A 72-year-old woman is hospitalized in Illinois in late August with a high fever and altered mental
status. Previously she was healthy, but has for the last several days experienced fever, headache,
cognitive decline, and difficulty walking. She is active outdoors, president of the local garden club, has
not traveled out of the area, and her husband is not ill. On admission, her temperature is 103.1˚F
(39.5˚C), and her heart rate is 120 bpm. On exam, she is disoriented, and her left leg is weak. Her CSF
shows 150 WBCs/mm3 (75% lymphocytes), 100 mg/dL glucose, and 90 mg/dL protein. Antibiotics are
given but she becomes increasingly obtunded. No bacteria are isolated from her blood or CSF. Five days
after admission, she has two generalized seizures, becomes deeply comatose, and requires mechanical
ventilation. Muscle tone is flaccid, and deep tendon reflexes are absent. She shows no signs of
improvement over the next 2 weeks, and life support is withdrawn on day 19 of hospitalization. CSF and
serum samples are positive for IgM antibody to an infectious agent.
Case 5. A 55-year-old avid outdoorsman residing in Texas County, Missouri, was bitten on the left ear by
a bat after allowing it to crawl up his arm and neck. He did not obtain medical care for the bite
immediately following the injury. Five weeks later, he goes to the local ED complaining of numbness and
pruritus of the left ear and face, headache, chest pain, and dysphagia. He is hospitalized and treated, but
over the next few days, his symptoms progress, and he shows steady neurological decline. He becomes
febrile, confused, and disoriented, and dies 7 days after admission.
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Fig. 1. Case 3.
M. Johnson and K. Watts, 10/8/24, 1 PM, CBTL
Case 6. A 64-year-old woman is brought to the ED after 5 days of fever, headache and confusion. A few
days before her present symptoms began, she had diarrhea for 2 days that resolved without treatment.
She has a history of rheumatoid arthritis for which she has been taking prednisone daily for the past
several months. On exam, she has a temperature of 101.8˚F (38.8˚C), a pulse of 102/min, a respiration
rate of 18/min and BP of 134/78 mm Hg. She is unable to answer simple questions and appears
agitated, but there is no nuchal rigidity nor focal neurologic deficits. Her CSF has 620 WBCs/mm3 (66%
neutrophils & 34% lymphocytes), 40 mg/dL glucose and 175 mg/dL protein. A Gram stain of the CSF
reveals a moderate number of neutrophils, but no organisms; however cultures of both the CSF and
blood grow a significant pathogen that has tumbling motility and is able to grow at 4˚C.
Case 7. During a 4-week period in August in a rural county in the Midwest, a total of 29 persons between
the ages of 9 and 15 years have a rapid onset of fever, headache, stiff neck and photophobia. Some
patients had diarrhea for a few days preceding the headache. Patient Q, who lives in this town, is an ill-
appearing 12-year-old boy in moderate distress due to a headache. He has some photophobia and mild
nuchal rigidity, but has a negative Brudzinski sign (flexion of the hip and knee when the neck is passively
flexed). His vital signs include a temperature of 102.6˚F (39.2˚C), pulse of 112/min, respiration rate of 16/
min, and blood pressure of 130/84 mmHg. His CSF has 54 WBCs/mm3 (92% lymphocytes), 65 mg/dL
glucose and 50 mg/dL protein.
Case 8. A 13-year-old boy presents with 3 days of vomiting, fever to 101.3˚F (38.5˚C), a severe
headache, agitation and confusion. Two weeks previously he visited the North Carolina mountains,
where he spent several days hiking. On physical examination, his vital signs are normal, his neck is
supple, and he does not have lymphadenopathy. His arms and legs have dozens of mosquito bite marks.
A lumbar puncture reveals 198 WBCs/mm3 (80% lymphocytes), 71 mg/dL glucose and 55 mg/dL protein.
Herpes simplex virus (HSV) PCR is negative, as is Rocky Mountain Spotted Fever and Lyme disease
serologic testing. A bacterial Gram stain and culture are also negative. During hospitalization his mental
status deteriorates, his heart rate drops to 30 to 40 beats/min, and he is intubated in the pediatric
intensive care unit. Head CT and MRI imaging scans show evidence of increased intracranial pressure.
He gradually improves and is discharged after 7 days of hospitalization when his mental status returns to
baseline. A serologic test reveals the etiologic agent of the disease.
Case 9. A 30-year-old woman is brought to the ED with a 2-week history of
progressively severe headache, nausea and vomiting; several seizures
have occurred over the past 2 days. She has been HIV positive for 3 years
and was diagnosed with AIDS a year before the current episode. She has
been on HIV therapy, but is currently failing her regime. Her brother can’t
recall any history of seizures. She appears in moderate distress from the
headache, but is able to answer questions. Mild right-sided weakness is
evident and an MRI reveals ring-enhancing lesions in both the left parietal
and right frontal lobes (Fig. 2).
Case 10. A 45-year-old man is brought to the ED because of fever, severe headache, nausea, vomiting
and mental status change that has been progressing over the past 2 weeks. The patient was diagnosed
with HIV two years ago and is not currently on antiretroviral therapy. On exam he has a temperature of
101.3˚F (38.5˚C), pulse of 106/min, respiration rate of 18/min, and BP of 110/62 mmHg. The patient is
lethargic and disoriented. Nuchal rigidity is noted as well as a positive Brudzinski sign. CSF: 80 WBCs/
mm3 (32% neutrophils & 66% lymphocytes), protein 68 mg/dL, and glucose 40 mg/dL. An India ink prep
of the CSF is diagnostic for the causative agent.
Case 11. A 28-year-old Hispanic man is brought to the ED for severe headaches and two generalized
seizures. Several weeks ago, he began having headaches that have now become more frequent. He
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Fig. 2. Case 9.
M. Johnson and K. Watts, 10/8/24, 1 PM, CBTL
denies fevers or chills. He is a recent immigrant from Mexico, but there is no
previous history of seizures. His CSF reveals 35 WBCs/mm3, with lymphocytic
and eosinophilic pleocytosis (increased cell count), protein of 62 mg/dL, and
glucose of 60 mg/dL. A CT scan of his brain reveals an intracranial calcified
cyst, and further imaging with MRI confirms the presence of similar lesions,
some with scolex visible (Fig. 3).
Case 12. A 39-year-old man with a history of injection drug use presents to
the ED with slurred speech, diplopia and dysphagia. A physical exam shows
bilateral ptosis, a sluggish pupillary response to light, bilateral 6th-cranial
nerve palsies (affecting vision in both eyes), and multiple skin abscesses on
his arms and legs. Shortly after admission, the dysphagia progresses,
necessitating intubation for airway protection. Electromyography suggests a disorder of neuromuscular
transmission and the causative agent is cultured from an abscess specimen.
Case 13. A 50-year-old man with a cadaveric renal transplant is rejecting the transplant despite
immunosuppressive drugs. He is now in renal failure with a blood pH of 7.31. Yesterday, he developed a
pain near his left eye that has become progressively more severe. On examination, his temperature is
99.5˚F (37.5°C), and the skin near his eye is swollen and necrotic. Microscopic examination of a lesion
biopsy reveals nonseptate hyphae with right-angle branching.