meningitis

Bacterial Meningitis, or Viral? The Dilemma of Equivocal Lab Results

Ashley Bechtol, MD; Rani Kharrubi, MD; and Pisespong Patamasucan, MD

A 16-year-old boy who recently had returned from a visit to Mexico presented to the emergency department complaining of fever, headache, vomiting, and neck pain for the past 2 days.

The first symptom he experienced was a throbbing headache with associated photophobia. Nonsteroidal anti-inflammatory drugs were tried at home prior to presentation, but they did not relieve the patient’s excruciating pain.

The headache persisted, and on the second day the pain woke him from sleep. He then experienced an episode of nonbloody, nonbilious emesis. The boy then began having fever and neck pain, at which time he decided to seek medical attention at the hospital.

He denied any insect bites or illnesses while in Mexico.

PHYSICAL EXAMINATION

On physical examination, the patient’s weight was 79.1 kg, temperature was 36.1°C, heart rate was 65 beats/min, respiratory rate was 15 breaths/min, blood pressure was 90/48 mm Hg, and oxygen saturation was 100% on room air. The patient had mild tenderness to palpation of the posterior neck, negative Kernig and Brudzinski signs, and otherwise normal neurologic examination findings. Cardiovascular examination showed regular heart rate and rhythm, no murmurs, and brisk capillary refill. Lungs were clear to auscultation, and the patient was in no distress.

LABORATORY RESULTS

A lumbar puncture was performed, the results of which revealed an elevated cerebrospinal fluid (CSF) white blood cell count of 1,400/µL, with 98% mononuclear cells and 2% polymorphonuclear cells, and a CSF red blood cell count of 150/µL. The CSF glucose level was in the normal range at 58 mg/dL, and the CSF protein level was slightly elevated at 60 mg/dL. Results of Gram staining showed a moderate amount of white blood cells, rare Gram-positive cocci in pairs, and rare Gram-positive bacilli.

What would be the logical next step?

A. Obtain CSF for enteroviral polymerase chain reaction (PCR) testing.

B. Verify the interpretation of the Gram stain results with the pathologist on call.

C. Start ceftriaxone and vancomycin therapy, and wait until CSF culture is negative at 72 hours.

D. Order magnetic resonance imaging and consult pediatric neurology.

(Answer and discussion on next page)

Answer: B, verify the Gram stain results

If a pathologist is able to confirm that the results of Gram staining are accurate and not the effect of a contaminant, the patient will receive more appropriate care. In this case, the Gram stain results were misleading, because a laboratory technician read the slide on a weekend, when a pathologist was not present. The initial reading was the presence of a moderate amount of white blood cells, rare Gram-positive cocci in pairs, and rare Gram-positive bacilli, which did not help to distinguish whether this patient’s illness had a viral etiology.

Practice pearl 1: Abnormal CSF test results, especially a white cell count greater than 1,000/µL, can occur in both aseptic and bacterial meningitis.1,2

Because of the lack of a definitive diagnosis, the second logical step was to treat the patient’s symptoms as a case of bacterial meningitis,3 and to obtain the CSF enteroviral PCR test results when available for a final diagnosis.

Practice pearl 2: PCR is the most reliable test for enterovirus infection, with a sensitivity of 96% to 100% and a specificity of 96%, and it is more rapid than culture testing.4

The turnaround time for PCR results varies greatly among commercial laboratories. In our city, it takes approximately 3 to 5 days for test results; on weekends, it takes even longer. This delay in diagnosis can lead to unnecessary hospital stay days, the administration of unnecessary antibiotics, and money spent unnecessarily on treatment for possible bacterial meningitis.

One solution to this dilemma for the clinician managing the case would be the availability in the city’s vicinity of high-priority PCR testing with a turnaround time of less than 24 hours. A faster positive enterovirus PCR test result could have saved our patient unnecessary hospitalization and reduced the cost of hospitalization.

Case Outcome

After 48 hours in the hospital, no organisms had grown in the CSF culture, and the patient was discharged home. After review with the pathologist, the initial findings on the CSF Gram stain slide were clarified as having been the result of a contaminant. Five days later, the enterovirus panel that had been sent out at the time of admission returned with positive results. With a positive identification of enterovirus, the patient had a good prognosis. After receiving the PCR test results, we called the patient at home, and he was doing well and denied any further headaches or emesis.

REFERENCES:

1. Smith AL. Bacterial meningitis. Pediatr Rev. 1993;14(1):11-18.

2. Ahmed A, Hickey SM, Ehrett S, et al. Cerebrospinal fluid values in the term neonate. Pediatric Infect Dis J. 1996;15(4):298-303.

3. Bryan CS, Reynolds KL, Crout L. Promptness of antibiotic therapy in acute bacterial meningitis. Ann Emerg Med. 1986;15(5):544-547.

4. DeBiasi RL, Tyler KL. Molecular methods for diagnosis of viral encephalitis. Clin Microbiol Rev. 2004;17(4):903-925.

Drs Bechtol, Kharrubi, and Patamasucan are in the Department of Pediatrics at the University of Nevada School of Medicine in Las Vegas.