Diagnosing Haemophilus influenzae and Meningococcal Disease: CDC's Lab Best Practices

A CDC laboratorian prepares for PCR testing. CDC.

Key points

• Invasive disease caused by Haemophilus influenzae (Hi) or Neisseria meningitidis (Nm) is diagnosed from the patient's clinical picture.
• Lab tests — culture and nucleic acid amplification such as polymerase chain reaction (PCR) — help confirm it, and also help spot outbreaks and shape the public health response.

CDC's best practices for state public health labs

Each lab should weigh these against its own capabilities.

1. Choose PCR tests that type the bacteria. A PCR assay for Hi and Nm should detect and tell apart all Hi serotypes (a–f) and the Nm serogroups common in the United States (B, C, W and Y).
2. Keep culturing. Labs with PCR should still grow cultures.
3. Culture alongside PCR. When PCR finds Hi or Nm, run a simultaneous or reflex culture.
4. Save the specimen. If culture isn't possible, keep an adequate clinical sample so another lab can test it with PCR or culture-free sequencing that identifies the serotype or serogroup.
5. Ask for help. A lab that can't determine serotype or serogroup should send specimens to CDC's Bacterial Meningitis Laboratory or an Association of Public Health Laboratories Vaccine Preventable Diseases Reference Laboratory.

Culture: strengths and limits

• Strengths: the gold standard, with virtually 100% specificity for Hi and Nm. Isolates allow serotyping and serogrouping, antimicrobial susceptibility monitoring, and whole-genome sequencing (WGS) — needed to compare strains in outbreaks and track vaccine effectiveness over time.
• Limits: both bacteria are fastidious growers, and culture is insensitive when specimens are mishandled or the patient has already had antibiotics.

PCR: strengths and limits

• Strengths: fast, highly sensitive and specific; it finds Hi and Nm DNA even when culture can't — including organisms killed by antibiotics, if enough DNA remains.
• Limits: WGS usually isn't possible on PCR-positive specimens without a culture (some labs can manage it when there's enough DNA), and PCR can't detect antimicrobial resistance.
• Case definitions: a PCR-positive result in an appropriate specimen counts as a confirmed case of H. influenzae or meningococcal disease.

What tests are available

• CDC's own assays: validated real-time PCR that detects Hi and all 6 serotypes (a–f), and Nm and 6 serogroups (A, B, C, W, X and Y), directly on isolates, cerebrospinal fluid and DNA extracted from serum.
• Commercial multiplex panels: tests such as BioFire's FilmArray Blood Culture Identification and Meningitis/Encephalitis panels and ARUP's Meningitis/Encephalitis panel screen one specimen for many pathogens. Used mainly in clinics, they identify Hi and Nm quickly, but most don't give the serotype or serogroup. (Trade names are for identification only.)

Why serotype and serogroup matter

They are key to spotting outbreaks and choosing the right response — prophylaxis for contacts and vaccination of people at higher risk. Vaccines protect against only certain types:

Sources

Based on "Best Practices for Diagnosis of Haemophilus influenzae and Neisseria meningitidis Disease," National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, March 6, 2026; a work of the United States government in the public domain.