41 cases of nongroupable N meningitidis conjunctivitis were identified at Joint Base San Antonio-Lackland, highlighting diagnostic, treatment, and surveillance implications for congregate living settings.
Outbreak
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An outbreak of 41 cases of Neisseria meningitidis conjunctivitis occurred among military trainees at Joint Base San Antonio-Lackland, Texas, between February and May 2025, according to CDC’s Morbidity and Mortality Weekly Report (MMWR). All affected trainees were young, otherwise healthy adults who had received the quadrivalent meningococcal vaccine. Despite widespread vaccination, the outbreak was linked to an unencapsulated (nongroupable) strain, identified by whole-genome sequencing.
Of the 41 patients, one developed periorbital cellulitis and required hospitalization with intravenous antibiotics. The remaining cases were successfully treated with topical antibiotics alone. No invasive meningococcal infections were reported.
Public health officials launched an investigation after two cases were identified within three weeks. A review of communal hygiene and cleaning practices found compliance with recommended protocols, and no specific outbreak source was identified. Whole genome sequencing confirmed the cases were genetically related.
A total of 41 cases of nongroupable N meningitidis conjunctivitis were reported in US military trainees despite quadrivalent vaccine coverage.
All patients recovered, with topical antibiotics proving sufficient in most cases and no invasive disease detected.
Whole genome sequencing was critical to confirming the outbreak strain and guiding the response, underscoring the role of laboratory surveillance in managing conjunctivitis outbreaks.
The findings underscore that, although viral and allergic conjunctivitis remain more common, N meningitidis can cause outbreaks in congregate settings such as military housing. Investigators emphasized the role of bacterial culture and sequencing in identifying etiology and guiding response strategies. Importantly, this outbreak suggests that nongroupable N meningitidis conjunctivitis in otherwise healthy individuals may be managed effectively with topical antimicrobials rather than systemic therapy.
“Characterization of the isolates early in the outbreak was critical to understanding the risk for invasive meningococcal disease. Without this information, systemic therapy might have been warranted rather than the successful topical-only approach used in this setting,” investigators noted.
The report notes two key limitations: only the first two isolates underwent whole genome sequencing, leaving the possibility of undetected strain variation, and the findings may not be generalizable beyond this cohort of young, healthy military trainees.
Background: Meningococcal Disease
Meningococcal disease refers to invasive infections caused by Neisseria meningitidis, a gram-negative diplococcus that colonizes the nasopharynx of up to 10% of healthy individuals. The most serious forms are meningitis and meningococcemia, both of which can progress rapidly and be fatal despite treatment. Case-fatality rates are 10%–15%, with up to 20% of survivors experiencing long-term complications. Vaccination (MenACWY, MenB) and antibiotic prophylaxis for close contacts remain the primary prevention strategies.
This outbreak demonstrates that N meningitidis can cause conjunctivitis clusters in communal environments, even among vaccinated populations. Rapid microbiologic characterization proved essential for guiding therapy, and findings suggest that nongroupable N meningitidis conjunctivitis in otherwise healthy individuals may be effectively managed with topical antimicrobials.
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