under the microscope
under the microscope
By Rodney Rohde, PhD, MS, SM( ASCP) CM, SVCM, MBCM, FACSc
Neisseria meningitidis Conjunctivitis Among Texas Military Trainees
Between Feb. 5,2025 and May 9, 2025, there was an outbreak of bacterial conjunctivitis among basic military trainees at Joint Base San Antonio-Lackland in San Antonio, Texas according to a report in the Centers for Disease Control and Prevention( CDC)’ s Morbidity and Mortality Weekly Report( MMWR). Among 11,797 trainees who began basic military training( BMT) during that period, 79 cases of mucopurulent( pus-forming) conjunctivitis were identified. Of those 79 cases, 41( 52 percent) were confirmed by culture to be Neisseria meningitidis, an uncommon agent for conjunctivitis. Another 32( 41 percent) were caused by Haemophilus species; the rest were other bacteria or unspecified.
Who Was Affected & Clinical Features
Affected individuals were healthy young adults( military trainees). All had recently received quadrivalent meningococcal vaccine( which covers N. meningitidis serogroups A, C, Y, and W) upon arrival. This vaccine doesn’ t target unencapsulated(“ non-groupable”) strains. Sex distribution: about 90 percent male, about 10 percent female among the confirmed N. meningitidis cases. Many had symptoms of a preceding upper respiratory infection: about 80 percent of N. meningitidis conjunctivitis cases reported this. The conjunctivitis was typically unilateral( one eye) in about 85 percent of cases.
Microbiology & Strain Information
The N. meningitidis isolates from the first two confirmed cases underwent whole-genome sequencing. They were found to be non-groupable( i. e. lacking the capsule genes usually associated with serogroups A, B, C, Y, W) and were of the same sequence type( ST-32), indicating that the cases were related. These non-groupable strains are less likely to cause invasive meningococcal disease( e. g. meningitis or bloodstream infection) because the capsule is a major virulence factor. The isolates also showed a mutation in the penA gene, consistent with decreased susceptibility to penicillin. No other major antibiotic-resistance genes were noted.
Response, Treatment, and Outcomes
After identification of the first two cases( within about a threeweek span in February), the base health surveillance team initiated an investigation and enhanced case finding. They set up active surveillance, encouraged cultures from ocular discharge, and established a registry for cases. Treatment: Most trainees with confirmed N. meningitidis conjunctivitis were treated with topical antibiotics( e. g. moxifloxacin, ciprofloxacin, or erythromycin). Signs of corneal involvement were monitored.
● One case had progression to periorbital cellulitis and required hospitalization and intravenous antibiotics— this was after delay in using topical moxifloxacin.
● No cases of invasive disease( i. e. meningitis, bacteremia) or corneal ulceration was reported.
Preventive measures: The investigation reviewed hygiene and cleaning practices( dormitories, showers, common areas), training activities, etc. Protocols were followed; no specific environmental source was identified.
Contact tracing and prophylaxis for close contacts were not broadly used, because current guidelines recommend prophylaxis chiefly for invasive disease. Additional vaccination wasn’ t deemed necessary given the nature of the strain.
Why This Outbreak Matters
● Unusual cause: N. meningitidis is classically associated with serious invasive disease but is a rare cause of bacterial conjunctivitis. Conjunctivitis outbreaks more often involve viral or allergic causes.
● Congregate living risk: Military trainees live in close quarters with communal dormitories which facilitate close contact and spread. Such settings require heightened surveillance for unusual pathogens.
● Implications for vaccine coverage: The quadrivalent vaccine does not cover non-groupable strains. This outbreak underscores that even vaccinated populations can have outbreaks from organisms outside vaccine coverage.
● Treatment paradigm: Because the strain was non-groupable and patients were healthy, topical antibiotics( instead of systemic therapy) were effective in nearly all cases. This may inform future guidelines in similar contexts.
Limitations and Questions Only the first two N. meningitidis isolates had whole-genome sequencing, so it remains possible that other cases involved slightly different strains or virulence factors. No environmental sampling( e. g. from surfaces, facilities) was done. Thus, the precise source or route of transmission remains unidentified. The findings may not generalize to other populations— these were young, immunocompetent trainees, under strict supervision, etc.
Recommendations and What to Do in Similar Situations In outbreaks of mucopurulent conjunctivitis, especially in congregate settings, clinicians should consider doing cultures of ocular discharge rather than assuming viral or allergic causes. Early microbial diagnosis helps guide treatment. When N. meningitidis is identified, whole-genome sequencing( or at least determinations of capsule gene presence and sequence type) should be used to assess risk of invasive disease and antimicrobial susceptibilities. For healthy people infected with non-groupable N. meningitidis, topical antibiotics may suffice, unless signs of more severe disease emerge. However, disruption or delay in treatment can lead to complications.
Broader Significance and Take-Home Messages
This outbreak is a stark reminder that even less common pathogens can cause outbreaks under the right conditions, especially in high-density living environments like military training bases. Vaccination remains crucial, particularly for preventing invasive disease caused by encapsulated N. meningitidis, but vaccine coverage has limits: non-vaccine strains or non-encapsulated organisms may still cause disease. Laboratory surveillance, including culture and genomic tools, is vital— not only diagnostic but also for guiding response( how aggressive treatment should be; whether prophylaxis needed; vaccination adjustment). Prompt recognition and treatment can prevent complications; in this event, most cases were resolved with topical treatments, with only one more serious case.
Rodney E. Rohde, PhD, MS, SM( ASCP) CM, SVCM, MBCM, FACSc, is the Regents’ Professor, Texas State University System; University Distinguished Chair & Professor, Clinical Laboratory Science( CLS); TEDx Speaker & Global Fellow – Global Citizenship Alliance; Texas State Honorary Professor of International Studies; Associate Director, Translational Health Research Initiative; Past President, Texas Association for CLS.
Source: Outbreak of Neisseria meningitidis Conjunctivitis in Military Trainees— Texas, February – May 2025 MMWR Weekly / September 4, 2025 / 74( 33); 516 – 521. https:// www. cdc. gov / mmwr / volumes / 74 / wr / mm7433a1. htm? s _ cid = mm7433a1 _ w
8 • www. healthcarehygienemagazine. com • sept-oct 2025