Meningococcal Conjunctivitis in Military Trainees
October 1, 2025 4 minutes read
By Stan Deresinski, MD, FACP, FIDSA
Synopsis: Forty-one cases of conjunctivitis due to Neisseria meningitidis occurred in vaccinated military trainees over several months at a Texas facility. Topical treatment alone was successful, and no cases developed invasive infection due to this unencapsulated strain.
Source: Ching SJ, Jung GO, Osuna A, et al. Outbreak of Neisseria meningitidis conjunctivitis in military trainees — Texas, February-May 2025. MMWR Morb Mortal Wkly Rep. 2025;74(33):516-521.
An otherwise healthy individual undergoing basic military training (BMT) in San Antonio, TX, presented for care on Feb. 5, 2025, with purulent conjunctivitis. Culture of the discharge yielded Neisseria meningitidis. Sixteen days later, a second trainee, but from a different training unit, also had purulent conjunctivitis due to N. meningitidis.
These cases occurred despite the fact that these and all other recruits receive a quadrivalent (Groups A, C, Y, and W) meningococcal vaccine within 72 hours of arrival for training. They also receive a single dose of penicillin G benzathine injectable suspension within seven days of arrival. Penicillin-allergic trainees receive weekly oral azithromycin to prevent streptococcal disease during training.
The identification of these two cases led to the establishment of a registry and of active surveillance for detection and characterization of additional cases. Identified cases were treated with topical erythromycin, ciprofloxacin, or moxifloxacin, and were referred for evaluation of possible corneal involvement.
A total of 79 cases of mucopurulent conjunctivitis was identified among trainees from Feb. 23 to May 9, 2025. Culture yielded N. meningitidis in 41 cases (52%). In addition, Haemophilus species were recovered in 32 (41%) cases. The 41 cases with N. meningitidis infection belonged to 37 different BMT units. No potential source of contamination could be identified.
Forty of the 41 patients had received benzathine penicillin on arrival for training. Of the 41, 35 (85%) had unilateral infection. Thirty-three patients (80%) reported having had symptoms of an upper respiratory tract infection. One patient had delayed onset of treatment and was hospitalized with periorbital cellulitis for which a brief course of systemic antibiotics was administered, but there were no cases of orbital cellulitis or of invasive corneal infection. Most importantly, there were no systemic infections.
Whole genome sequencing (WGS) of the N. meningitidis isolates from the two initial cases demonstrated they were from the same sequence type and were closely related. They also were non-groupable, lacking genes responsible for encapsulation. In addition, a mutation in the penA gene indicated they had reduced susceptibility to penicillin.
Commentary
In contrast to the lack of invasive infection in this series, Parikh and colleagues previously reported that a literature review indicated that there was a 10% to 29% risk of invasive infection within two days of onset of primary meningococcal conjunctivitis.1 They also reported evidence of a significantly reduced risk of invasive meningococcal disease when patients received systemic antibiotics rather than topical antibiotics alone, as were used in the trainees. They recognized that invasive meningococcal disease has been reported in several individuals who had been close contacts of patients with meningococcal conjunctivitis and, despite recognition of the limited evidence, they recommended that contacts receive antibiotic prophylaxis. However, in the outbreak reviewed here, contact tracing was not performed because the cases were noninvasive and were caused by a non-groupable strain. Furthermore, the Centers for Disease Control and Prevention indicates that “chemoprophylaxis is not recommended for close contacts of patients with evidence of N. meningitidis only in non-sterile sites such as an oropharyngeal swab, endotracheal secretions, or conjunctival swab.”2
Of note is that WGS detected a mutation in the penA gene in the isolates from the two initial cases, indicating apparent reduced susceptibility to penicillin, although no phenotypic testing is reported. Rodriguez and colleagues have indicated that nonsusceptibility to penicillin has increased globally during the past 30 years and that, since 2016, there has been a significant increase in penicillin-resistant isolates with minimum inhibitory concentrations (MICs) ≥ 0.5 mcg/mL.3 This reduced susceptibility has been associated with mosaic penA alleles or with the beta-lactamase genes (blaROB-1 and blaTEM-1).
The patients in this series were treated only with topical antibiotics. None developed locally (i.e., cornea) invasive or systemically invasive infection. Of note is that the patients were immunocompetent, had recently received quadrivalent meningococcus vaccination, and the infections apparently were caused by organisms that lacked encapsulation. The capsule allows serotyping and is a critical virulence factor of the organism.
Stan Deresinski, MD, FACP, FIDSA, is Clinical Professor of Medicine, Stanford University.
References
1. Parikh SR, Campbell H, Mandal S, et al. Primary meningococcal conjunctivitis: Summary of evidence for the clinical and public health management of cases and close contacts. J Infect. 2019;79(6):490-494.
2. Centers for Disease Control and Prevention. Chapter 8: Meningococcal Disease. Manual for the Surveillance of Vaccine-Preventable Diseases. Oct. 8, 2024. https://www.cdc.gov/surv-manual/php/table-of-contents/chapter-8-meningococcal-disease.html
3. Rodriguez E, Tzeng Y-L, Berry I, et al. Progression of antibiotic resistance in Neisseria meningitidis. Clin Microbiol Rev. 2025;38(1):e0021524.
Forty-one cases of conjunctivitis due to Neisseria meningitidis occurred in vaccinated military trainees over several months at a Texas facility. Topical treatment alone was successful, and no cases developed invasive infection due to this unencapsulated strain.
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