# Presentation: 169162

## Aseptic Meningitis Epidemic in an Area of  Intense West Nile Virus Epizootic Activity  Baltimore, Summer 2001

- K. Julian, J. Mullins, A. Olin, H. Peters, S. Oberste,
- J. Lovchik, A. Bergmann, R. Brechner, R. Myers,
-  A. Marfin, and G. Campbell

**PRELIMINARY**

**Notes:**
I’d like to report an investigation of an aseptic meningitis outbreak that occurred in the setting of a West Nile virus epizootic, in Baltimore, summer of 2001.

## Background: Aseptic meningitis syndrome

- Acute onset fever, headache, neck pain/stiffness, vomiting, meningeal signs
- No confusion/stupor
- CSF:
-  WBC
-  protein
- normal glucose
- Negative bacterial culture of CSF

**Notes:**
First I would like to discuss some background on aseptic meningitis. Aseptic meningitis is not a single disease but a general syndrome—common symptoms include fever, headache, neck pain/stiffness, vomiting and physical exam signs indicating meningeal irritation. As a general distinction from encephalitis, no confusion or major mental status changes are present in patients with aseptic meningitis syndrome. 

Cerebrospinal fluid (or CSF) demonstrates an elevated WBC count, usually lymphocytic, modestly elevated protein, and usually normal glucose.

As befitting the “aseptic” description, bacterial culture of CSF is negative. 

## Background: Aseptic meningitis in U.S.

- Viruses
- Enteroviruses
- Arboviruses (SLE, LAC, WNV)
- Herpesviruses (HSV 2, HSV 1, EBV, HHV 6, VZV)
- HIV
- Lymphocytic choriomeningitis? Mumps?
- Numerous other causes
- e.g., Lyme disease, leptospirosis, 2o syphilis, partially-treated bacterial meningitis, parameningeal disease, TB, cryptococcus, autoimmune disease, medications

**Notes:**
The aseptic meningitis syndrome is generally perceived to have a viral etiology, although certainly other infectious and non-infectious etiologies have been implicated. 
As an etiologic agent, I would like to emphasize “enteroviruses” because they appear to dominate the scene, causing over 80% of cases of aseptic meningitis with known etiology (Rotbart in Infections of the CNS—based on 8 epi studies from 1941-1990). 
Arboviruses such as SLE would be expected primarily to cause meningitis in epidemic settings, while La Crosse viruses occur endemically, primarily in Appalachia and the Midwest. And now we should add WNV to the U.S. list.
Other viruses including the herpesgroup, HIV, LCM are thought to be important causes of aseptic meningitis. 
Although not necessarily common, I have included this partial list of the variety of spirochetes, other bacterial, fungal, autoimmune disease and medications that cause aseptic meningitis. 

## Background: WNV meningitis in U.S.

- Relative contribution of WNV to all aseptic meningitis?
- U.S. 1999-2000:
- 		21 persons hospitalized with WNV meningitis
- 		52 persons hospitalized with WNV encephalitis
- Selection bias in U.S. surveillance:
- 		WNV testing prioritized for encephalitis > meningitis

**Notes:**
WNV is known to cause meningitis.
However, the relative contribution of WNV as a cause of all cases of aseptic meningitis in the U.S. is not known. In U.S. 1999-2000 surveillance detected 21 persons hospitalized with WNV meningitis, and 52 persons hospitalized with WNV encephalitis or meningoencephalitis. 
However, there is probably a type of “selection bias” in U.S. surveillance—in many states WNV testing is prioritized for patients with encephalitis over patients with meningitis. As a result, cases of WNV meningitis potentially could be missed. 
An investigation of an aseptic meningitis epidemic in Baltimore provided an opportunity to assess the role of WNV meningitis in the context of the most common known cause of aseptic meningitis: enteroviruses 

## Background: Aseptic meningitis cases reported from Baltimore, Jun 1-Sep 30

- Data source: Maryland Dept of Health & Mental Hygiene (DHMH)

**Notes:**
In late August 2001, Maryland’s state health department recognized an increase in reports of aseptic “viral” meningitis, (a reportable disease in Maryland). This graph shows the number of cases each summer over the past 5 years in Baltimore City and County. A specific etiology was not reported in 94% of the 2001 cases.

## Background: WNV avian epizootic Maryland, 2001

- Data source: ArboNET—WNV surveillance system

**Notes:**
Concurrently, an intense WNV epizootic among birds was detected in Maryland, with the most numbers of dead WNV-infected birds identified in the Baltimore area.
Early in the season in certain areas of Baltimore, nearly 100% of tested dead birds were found to be infected with WNV. 

14 positive mosquito pools were identified in Baltimore before Sept 30. 
One case of WNV encephalitis in a human had been reported by early September.

## Objectives

- Describe apparent aseptic meningitis epidemic
- Estimate relative contribution of WNV and enteroviruses
- Assess WNV surveillance among patients reported with aseptic meningitis

**Notes:**
An investigation was initiated in September 2001. Objectives included
 Describe the apparent aseptic meningitis epidemic
 Estimate relative contributions of WNV and enteroviruses to this outbreak 
 Assess WNV surveillance testing strategies among patients with aseptic meningitis.
An investigation was initiated in September 2001. Objectives included
 Describe the apparent aseptic meningitis epidemic
 Estimate relative contributions of WNV and enteroviruses to this outbreak 
 Assess WNV surveillance testing strategies among patients with aseptic meningitis.

## Methods: Case ascertainment

- 6 Baltimore hospitals
- Cases identified by
- reports to DHMH
- lab results with WBC in CSF
- discharge diagnoses codes
- Medical chart review

**Notes:**
The investigation focused on the 6 Baltimore City & County hospitals which reported the most (73%) of the summer season cases. 
Cases were identified by different means, depending on hospital resources. Primarily cases were identified by reports to the state health dept, but additional cases were also identified by screening lab reports for elevated WBC in CSF, and by review of discharge diagnoses codes.
Medical charts were reviewed for each patient for case confirmation, and to collect results of diagnostic tests. 

## Methods: Case definition

- Baltimore City or County resident
- Onset Jun 1-Sep 30, 2001
- >5 WBC in CSF
- Negative bacterial cultures of CSF
- No evidence of fungal or parasitic CNS disease, cerebral hemorrhage, carcinomatous meningitis, cerebral vasculitis, or encephalitis

**Notes:**
The investigation was limited to persons living in Baltimore City or County who developed an acute illness with onset between June 1 and Sept 30, 2001 evaluated at one of the 6 investigation hospitals. Cases had greater than 5 WBC in the CSF and negative bacterial cultures of CSF. Patients were excluded who had evidence of fungal or parasitic CNS disease, cerebral hemorrhage, carcinomatous meningitis, cerebral vasculits or encephalitis. 

Note: Although encephalitis cases were identified during the investigation, for the purposes of this presentation on aseptic meningitis, we will not discuss encephalitis cases here.

## Methods: Specimen collection and interviews

- Acute-phase
- CSF
- Serum
- Rectal or nasopharyngeal swabs
- Convalescent-phase (age >12 years, unknown etiology)
- Serum
- Standardized interview: symptoms, duration

**Notes:**
Whenever available, aliquots of previously collected acute-phase CSF, serum, and occasionally rectal swab and nasopharyngeal swab specimens were obtained for additional testing. (Because the investigation was conducted towards the end of the outbreak, most acute specimens were obtained from hospital, state health dept lab, or private reference laboratory storage)
For convalescent phase specimens: for consenting patients age greater than 12 years with aseptic meningitis of unknown etiology, home-visits were arranged to obtain a convalescent-phase blood sample (for antibody testing to rule-out WNV) and to conduct a standardized interview focusing on symptoms and duration of illness. 

## Methods: DHMH and CDC testing

- CSF
- WNV IgM ELISA
- Enteroviral culture, typing by PCR
- Serum (acute- & convalescent-phase)
- WNV IgM ELISA
- IFA for SLE, CE, EEE, WEE
- Nasopharyngeal and rectal swabs
- Enteroviral culture, typing by PCR

**Notes:**
After hospital testing was completed, collected specimens underwent additional testing at Maryland state lab and CDC: Testing focused on CSF:  WNV IgM ELISA, and viral culture for enteroviruses. Enteroviral isolates were typed by PCR methods.              
Acute and convalescent phase serum was also tested for WNV IgM as well as IFA screens for IgM and IgG to several arboviruses.
Nasopharyngeal and rectal swab specimens were tested for enteroviruses by viral culture.

[If from Eastern shore, patients tested for EEE IgM ELISA]
[If WNV IgM ELISA positive, then WNV IgG ELISA and SLE IgM and IgG ELISA]

## Results: 113 aseptic meningitis cases

| Age | 18 years (1 wk – 74 y) |
| --- | --- |
| Gender | 56% male |
| Residence | Widely distributed |
| Severity
Hospitalization	 | 
2 (0 – 11) days |
|      Fatalities                                None known |  |

**Notes:**
Unless otherwise specified, for the remainder of this discussion, I will focus on the 113 cases of aseptic meningitis identified during the investigation at 6 hospitals in Baltimore, onsets between June 1-September 30, 2001
General characteristics of the cases: Median age was 18 years.
56% were male. Residences were widely distributed. 
As a proxy for severity of illness, median duration of hospitalization (n=111) was 2 days, with range 0-11 days. No fatalities occurred during hospitalization nor were reported to Maryland state health dept.

## Results: Week of illness onset

**Jun 3**

**Jul 1**

**Jul 29**

**Aug 26**

**Sep 23**

**Notes:**
Cases occurred primarily in August and early September, a pattern which may be observed with WNV or enteroviruses. 

## Results: Clinical characteristics ( n = 33 )

- Symptoms recalled
- 100% headache
- 85% fever
- 85% eye pain or sensitivity to light
- _Symptoms duration_		_Work/School Missed_
**18** (5 – 47)  days		**9** (0 - 30)  days

**Notes:**
For additional clinical characteristics, 33 patients were interviewed at the time of collection of convalescent-phase serum. Headache was prominent in all patients, and many reported fever and eye pain or photophobia. 
Symptoms lasted a median of 18 days.
Long duration of illness primarily was related to fatigue and persistent headaches. 
For those who worked or attended school [24 patients], a median of 9 days was missed.

Note: This is minimum symptom duration. 12 persons had not fully recovered at the time interview. For these persons, minimal duration of illness was calculated by Interview date – onset date. So this is probably is an underestimate.

## Results: CSF characteristics

|  | n | median | range |  |
| --- | --- | --- | --- | --- |
| Protein | 111 | 53 mg/dL | 10 - 215 mg/dL | Elevated in 52% |
| Glucose  | 110 | - | - | Normal in 99% |
| WBC | 113 | 135     per mL | 7 - 1083 per mL | Mononuclear predominance in 59% |

**Notes:**
CSF demonstrated
Protein elevated in 52%  [for 111 patients with data, using 50 as upper limit of normal] 
Glucose normal in 99% [for109 of 110 patients with data, using 40mg/dL as lower limit of normal]. 
As part of the case definition, WBC counts in CSF were elevated. 59% had a predominance of mononuclear cells. 

## Results: Diagnoses

- 44 enteroviral meningitis
- 						       _# cases_
- 			Echo 13		     	14
- 			Echo 18		     	10
- 			Coxsackievirus B2		5
- 			Echo 6				1
- 			Echo 30			1
- 			Enterovirus 70/71		1
- 			Not typed			12
- 2 HSV meningitis
- 1 Lyme meningitis
- 66 undetermined etiology

**Notes:**
44 enterovirus cases were diagnosed by culture of CSF, rectal swab, nasopharygeal swab, or by PCR of CSF. 
The most commonly serotype was echovirus 13, although 5 other serotypes were identified. 
2 HSV and 1 Lyme meningitis were identified by testing ordered by treating physicians.

## Results: Enterovirus meningitis, by age

| Age group (in years) | N 
cases |  # tested for enterovirus | % test-positive enterovirus |
| --- | --- | --- | --- |
| <1 | 12 | 10 | 80% |
| 1-10 | 24 | 16 | 94% |
| 11-20 | 29 | 23 | 52% |
| 21-30 | 11 | 4 | 75% |
| 31-40 | 26 | 13 | 38% |
| 41-50 | 5 | 3 | 33% |
| >50 | 6 | 2 | 0% |

**Notes:**
This chart examines different age groups. Let’s focus on the first and last columns. The first column shows the age groups. As you see in this last column, the % of tested patients who were positive for enterovirus, enterovirus meningitis was most commonly identified in children. However, as has previously been reported by other studies, it also appears as if enterovirus is an important cause of aseptic meningitis in adults. 

## Results: 66 cases undetermined etiology

- _Characteristics_
- Age: median 26 years (2 wk – 67 y)
- 5 HIV+
- 4 prior history of meningitis
- _Documented negative tests for these 66 cases:_
- 45 patients with 1 WNV IgM test (including 23 convalescents)
- 27 with 1 enterovirus test
- 17 with 1 *B. burgdorferi* Ab test
- 11 with 1 HSV test

**Notes:**
For 66 cases, etiology was not determined. Median age of this group of patients was 26 (older than the enterovirus group), 5 were known to be HIV+, 4 had a prior history of meningitis. 
What testing was done on these patients?
There were documented negative tets for 
45 patients had at least 1 WNV IgM test, including 22 with convalescent serum and 1 “convalescent”: day 10 CSF. 
27 patients with at least one type of enteroviral test [10 of these were likely of poor quality with long suboptimal storage] 

## Pre-investigation surveillance testing  

- Reported cases—etiology reported in ~5%
- WNV testing 1st priority at state
- Patients >17 years-old hospitalized with meningitis
- 37% cases  1 WNV IgM test
- IgM tests of acute CSF
- Convalescent serum requested, but rarely received—collection not feasible
- Enterovirus/other common agents testing                       _not_ routinely incorporated

**Notes:**
As described, the objectives of the investigation included a description of issues faced in Maryland’s WNV surveillance among patients with aseptic meningitis. 
We’ll focus on the pre-investigation situation, during routine surveillance.
Of aseptic meningitis cases reported to the state health dept, an etiology was reported in only about 5%. Diagnosis of a specific etiologic agent is often not pursued by treating physicians, or the results of testing were not available at the time the case was reported.
Because of the urgency of detecting WNV human epidemics, WNV testing was the first priority in aseptic meningitis testing at the state level. And because the vast majority of reported # of cases were of unknown etiology, WNV testing was in effect used as a first-line test. 
Policy prioritized WNV testing for aseptic meningitis patients >17 years-old. [Later this criteria was expanded to aseptic meningitis patients >5 years-old. ]
37% of the 113 investigation cases had at least 1 WNV test performed at the state level independent of the investigation. 
Tests focused on detection of IgM in acute CSF—Fewer serum samples were tested.
Convalescent serum was requested by the state health dept, but only very rarely received. For patients with negative tests on acute specimens, collection of convalescent samples was generally not feasible. 
Enteroviruses or other common agents testing was not routinely incorporated into aseptic meningitis surveillance. 

## Results: Investigation testing yield 

| # case-patients with   | N | #  positive (%) |  |
| --- | --- | --- | --- |
|  1 WNV IgM ELISA | 69 | 0 | (0%) |
|  1 Enterovirus culture or PCR | 71 | 44 | (39%** - 62%) |

- ** Lowest possible % if N were 113

**Notes:**
Because it turned out that this was a non-epidemic year for WNV in Baltimore, WNV testing used as a first line procedure was low yield. Here we are looking at testing results after the investigation was completed. Of 69 case-patients with at least 1 WNV IgM test, 0 were positive. By contrast, enterovirus positivity was up to 62% of case-patients known to be tested. 

## Limitations

- Limited population
- Subset of Baltimore hospitals
- Subset of patients within these hospitals
- Specimens not available for all patients
- Testing not comprehensive

**Notes:**
Before we reach our conclusions, several limitations should be acknowledged and caution generalizations.
Although at least 13 acute-care medical centers are in the Baltimore area, we focused on the subset of 6 hospitals reporting the most cases. And within each hospital, we were only able to review data on a subset of readily identifiable patients. 
Specimens were not available for all patients—we relied on availability of acute specimens serendipitously found in storage, or by labor-intensive collection of convalescent specimens.
Testing was not comprehensive, but focused on WNV and enteroviruses. 

## Was WNV meningitis missed?

- Not all patients tested
- False negatives possible:
- Tested too early?
- 79% patients presented by day 3
- WNV IgM takes time to develop
- Tested too late?
- Convalescents collected on days 12-111
-  WNV IgM eventually declines

**Notes:**
It is also possible that cases of WNV meningitis were missed in this investigation.
Not all patients of unknown diagnosis were tested [Although, most did have at least 1 WNV IgM test, 21 of the undiagnosed patients had no WNV tests at all) primarily because lack of acute specimens, insufficient resources to arrange collection of convalescent specimens, or ineligibility of (16) patients <=12 years old  for convalescent specimen collection]
Even of the patients tested, false negatives were possible. 
Patients tend to present early—the severity of the headache and other symptoms often brings people in fairly promptly—78% presented by illness day 3.
CSF is usually only collected once—on presentation. The problem with WNV serologic tests of these acute specimens—WNV IgM may not have developed at the time of presentation/sample collection.
For convalescent-phase testing, samples were collected on days 12-111 (median day 40). Although the kinetics of WNV IgM antibody are not fully understood, with time, WNV IgM would be expected to decline.

## Missed WNV meningitis?—estimates

**113 cases**

**47 with diagnosis**
**(no WNV)**

**66 withOUT diagnosis**

_**Sample**_**: 23 convalescent WNV test-negative**

-   Best guess: **0%** of 66 WNV positive
-   Upper limit of 95% confidence interval: **10%**

**Notes:**
What are the chances that we missed cases of WNV meningitis? We can make an estimate. 
Of the 113 cases, 47 were determined to have a specific diagnosis (enteroviruses, lyme diseases, or HSV)—we can presume that none of these persons also had WNV dual infection. 
That leaves 66 cases without a specific diagnosis. 
We were able to test a “sample” of these patients. We know that 23 were test negative for WNV IgM on convalescent sample—we will assume that this effectively rules out WNV in this sample of 23 patients. 
So based on our sample, our best guess is that 0% of the 66 undiagnosed patients had WNV infection. But how sure are we? We calculated the upper limit of our 95% confidence interval to be 10%. Which means that based on these assumptions, we’re quite sure that we did not miss more than 6 or 7 cases of WNV meningitis. 

## Conclusions: Aseptic meningitisBaltimore, summer 2001

- Despite WNV avian epizootic,
- 		no apparent WNV meningitis epidemic
- Enteroviruses predominant identified cause of aseptic meningitis in children and adults
- Echovirus 13 most common

**Notes:**
Conclusions:  
Despite an intense WNV avian epizootic in Baltimore, summer 2001, there was no apparent WNV meningitis epidemic. It should be noted that through routine surveillance, three cases of WNV encephalitis were identifed at the 6 investigation hospitals, and a total of 5 WNV encephalitis cases were found in the Baltimore area. But there was no evidence that these encephalitis cases were the tip of an iceberg of WNV meningitis epidemic. 
Consistent with epidemiologic studies of aseptic meningitis, enteroviruses were the predominant identified cause in both in children and adults. Although this is only an estimate with potential selection biases, approximately 60% of patients tested for enterovirus were positive. 

Echovirus 13 was the single most commonly identified agent. Five other serotypes were also identified. But finding any echovirus 13 is relatively unusual. Although previously rarely detected, in 2001 echovirus 13 was associated with aseptic meningitis outbreaks in multiple US states. Although multiple enteroviral serotypes were circulating in Baltimore and it may be difficult to implicate a single agent, it is possible that echovirus 13 accounted for the excess number of cases of aseptic meningitis in Baltimore. 

## 
WNV testing often done before more common agents

As first-line test in non-epidemic years,            
	 WNV IgM serology low yield

- WNV testing often done before more common agents
- As first-line test in non-epidemic years,
- 	 WNV IgM serology low yield

- Conclusions: WNV surveillance among aseptic meningitis cases

**Notes:**
Regarding WNV surveillance:
WNV testing was often done before testing for enterovirus or other common causes of aseptic meningitis. Or if other testing was done, positive results were not communicated to state lab in a timely manner. 
As a first line test in non-epidemic years, WNV IgM testing may be of low yield. But of course during WNV epidemics, the situation may be very different.

## Testing common and/or treatable causes of aseptic meningitis

- Rapid (PCR) tests for enterovirus available
- Provide specific diagnosis for most patients
- Reduce logistically difficult WNV IgM testing
- Reduce unnecessary anti-bacterial agent use
- Treatment (Pleconaril) for enteroviral disease may become available
- Treatable : Lyme disease, herpes simplex, varicella-zoster, HHV-6, cytomegalovirus(?)

**Notes:**
Before any recommendations may be proposed, I would likely to briefly review some issues regarding testing of common or treatable causes of aseptic meningitis.
Rapid (PCR) tests for enterovirus (as well as for herpesviruses and others) are available and effective. 
Because enteroviruses are so common as a cause of meningitis, enteroviral PCR potentially could provide a specific diagnosis for most patients.
Enterovirus PCR testing may also reduce logistically difficult WNV IgM testing and potentially reduce unnecessary empirically started antibiotics. 
Treatment of enteroviral disease may soon become available—the drug pleconaril has been used in clinical settings and is currently being assessed for broader use.
There are other causes of meningitis (with already available treatment) which might be appropriate to target for diagnosis, including Lyme disease, herpes simplex, varicella zoster, human herpes virus 6, and potentially CMV

## Considerations for (WNV) meningitis surveillance: Tiered testing

- First**:** Rapidly exclude common and/or treatable agents
**ENTEROVIRUSES**
- Herpesviruses
- If immunocompromised patient, may expand panel

**Notes:**
Now we can consider a slightly amended approach to WNV surveillance among patients with aseptic meningitis. 
It may be appropriate to develop an algorithm for tiered testing. 
As in any situation, first priority would be to insure diagnostic testing for common and/or treatable agents was completed—use of PCR tests for enteroviruses and herpesviruses may be appropriate. 
Note: If patients are immunocompromised, the patient’s treating physicians will have expanded the diagnostic testing panel greatly.

## Considerations for (WNV) meningitis surveillance: Tiered Testing

- First: Rapidly exclude common and/or treatable agents
**ENTEROVIRUSES**
- Herpesviruses
- If immunocompromised patient, may expand panel
- Second: Consider WNV IgM testing
- WNV ELISA IgM screen of acute CSF & serum
- If early (<8 days),
- 		WNV ELISA IgM of >day 7 serum

**Notes:**
Secondly, if the first-line tests are all negative, WNV testing may be considered. Other markers of WNV activity should be taken into account. If a region (for example, in the far west) has never shown any animal or human WNV activity, it may not be efficient to pursue aggressive WNV testing of humans with aseptic meningitis. However, if instead WNV activity (animals and/or humans) is detected in a region, or in a neighboring region, there should be a lower threshold for conducting WNV testing. 
If WNV testing is conducted for patients with aseptic meningitis, it may be necessary to collect specimens after day 7 to adequately rule-out WNV. This can be logistically difficult if the patient has been discharged to home. But hopefully, with this tiered approach to testing, most patients will already have been in effect ruled out for WNV by the identification of an alternate diagnosis of one of the most common and/or treatable agents.

## Acknowledgements

- Maryland DHMH epidemiology & laboratories
- Baltimore City and County Health Dept
- REVB-CDC epidemiology & laboratories

- Infection control practitioners: Kathy Arias, Ruth Bertuzzi, Colleen Clay, Jeanne Brown, Diane Lagasse, Polly Ristiano, Donna Feldman, Phyllis Tyler, Joanne Venturelli, Matt Wallace
- and laboratory, medical records & emergency dept staff at the investigation hospitals

**Notes:**
A very large number of persons contributed to this investigation. I would especially like to thank the infection control practitioners at the investigation hospitals, as well as many others at health departments and laboratories. 

## Aseptic meningitis cases identified at   6 Baltimore hospitals by ICD-9 codes— admissions Jun 1-Sep 30