Meningococcal Conjunctivitis Outbreak Among Military Trainees, Texas, 2025

Most conjunctivitis in healthy adults is viral or allergic, and Neisseria meningitidis is an uncommon cause of the bacterial kind. So when two healthy trainees at Joint Base San Antonio-Lackland, in San Antonio, Texas, turned up with meningococcal conjunctivitis in February 2025, base health officials investigated. By May, they had found 41 cases. A report by military physicians and epidemiologists at the base, Brooke Army Medical Center and the Uniformed Services University describes what happened.

Life in basic training

U.S. Air Force basic military training takes place at Joint Base San Antonio-Lackland. About 900 trainees enter and graduate each week, organized into groups of about 52. Trainees live in dormitories that typically hold 50 to 60 people, sleeping in beds arranged head-to-foot, and follow a standard 7.5-week curriculum, so each class has much the same activities and exposures week by week.

To prevent outbreaks of invasive disease, every trainee gets the quadrivalent meningococcal vaccine (groups A, C, Y and W; Menveo) within 72 hours of arrival and a single injection of penicillin G benzathine against streptococcal disease within 7 days. Trainees allergic to penicillin take oral azithromycin weekly instead.

The first cases

On February 5, 2025, a healthy trainee was diagnosed with meningococcal conjunctivitis after 2 days of mucus-and-pus discharge from one eye. The symptoms first suggested a virus, but the heavy discharge led the provider to culture it, and 6 days later it grew N. meningitidis. On February 21, a trainee from a different unit came in with the same heavy discharge from one eye and swelling around it, but no damage to the cornea. That culture also grew N. meningitidis, raising concern about invasive meningococcal disease.

Both trainees had started training 2 weeks apart, and both fell ill in their fourth week.

Searching for more

On February 23, the day the second result arrived, the base's Trainee Health Surveillance team, epidemiologists and preventive medicine physicians who watch over the trainee population, set up a registry and began active surveillance. Base clinicians were asked to culture discharge from every patient with conjunctivitis and report cases, instead of treating without a culture as usual. Patients with confirmed meningococcal conjunctivitis got antibiotic eye drops or ointment (erythromycin, ciprofloxacin or moxifloxacin) and an eye exam to check the cornea.

From February 23 to May 9, 79 cases of conjunctivitis with discharge were found among 11,797 trainees who started training, 6.7 per 1,000:

Of the 41 meningococcal cases, 23 (56%) came within a month of the second case.

Positive eye cultures among trainees by date and pathogen, February 5–May 9, 2025. MMWR.

The two bacteria struck at different stages of training: 29 of the 32 Haemophilus cases (91%) appeared in the first 3 weeks, while 36 of the 41 meningococcal cases (87.8%) appeared in the fourth week or later.

Positive eye cultures by week of training and pathogen, with cumulative percentage. MMWR.

The patients

The 41 meningococcal cases came from 37 different training groups. Men made up 78% of trainees but 90% of cases. Most patients (80%) had had an upper respiratory infection first, and 85% had only one eye affected. All improved within 24 hours of starting eye drops. One patient, whose treatment was delayed, developed periorbital cellulitis and needed a short course of intravenous antibiotics. No one developed corneal ulcers or orbital cellulitis. Antibiotics for close contacts were not given, because they are recommended only for contacts of invasive disease. Notably, Haemophilus infections occurred in trainees who had received either penicillin or azithromycin, but meningococcal infections occurred only in those who had received penicillin.

What sequencing showed

Isolates from noninvasive meningococcal infections are not usually serogrouped or sequenced. Here, to guide the response, the first two isolates underwent whole genome sequencing. Both were nongroupable: they lacked the genes for a capsule, which suggested a low risk of invasive disease. Both were sequence type 32 and closely related. ST-32 has been linked to outbreaks of invasive serogroup B disease, but without a capsule this strain was not expected to cause invasive disease in healthy people. The isolates carried a penA gene mutation that reduces susceptibility to penicillin, and no other resistance markers.

Looking for a source

The team inspected dormitories, showers and common areas and reviewed cleaning protocols; no environmental samples were taken. It also examined fourth-week field training. Gas masks were cleaned and sanitized with bleach at the recommended strength; CPR training carried little risk because trainees did not practice rescue breaths on the mannequin; and at the shooting range, safety goggles were not shared and were wiped with hypochlorite after each session. The team visited training sites and gave training staff a CDC infographic on preventing conjunctivitis. Because the infections were noninvasive and the strain nongroupable, neither preventive antibiotics for contacts nor extra vaccination was recommended. No source was found.

What it means

The authors found no earlier report of an outbreak of meningococcal conjunctivitis. All the patients had recently been vaccinated, but the quadrivalent vaccine is not expected to protect against unencapsulated strains. Conjunctivitis arises from bacteria placed directly on the eye's membranes, without entering the blood or nervous system. Carriage of N. meningitidis in the nose and throat can reach 5%–10% in some U.S. populations and peaks at 23.7% at age 19, the age of many trainees, so many were probably carriers; yet invasive disease is rare, with only one previous case of meningococcal meningitis among trainees at the base, in 2021.

Some countries recommend systemic antibiotics for meningococcal conjunctivitis, based mostly on studies in children before vaccines were widely used; the United States does not. In this outbreak, eye drops alone worked. The authors suggest the outbreak may be linked to the strain's reduced penicillin susceptibility combined with the fall in blood levels of benzathine penicillin about 3 weeks after the injection, though no definitive cause was found. Where isolates cannot be characterized, systemic treatment might still be warranted.

Limitations: only the first two isolates were sequenced, so other strains may have entered or the strain may have changed during the months-long response, though all cases responded to the same treatment; and the findings, from healthy young trainees, may not apply to other groups.

The report concludes that serogrouping noninvasive meningococcal isolates can guide an outbreak response, and that nongroupable meningococcal conjunctivitis in healthy people may not need systemic treatment if it is identified promptly and treated appropriately, even in crowded living quarters.

Sources

• Ching SJ, Jung GO, Osuna A, et al. "Outbreak of Neisseria meningitidis Conjunctivitis in Military Trainees — Texas, February–May 2025." MMWR 74(33). https://www.cdc.gov/mmwr/volumes/74/wr/mm7433a1.htm
• The report dates the training-site visits to February 13–18, "after identification of the first two cases," though the second case was identified on February 21; this page gives no date for the visits. It also once spells the bacterium "N. meningitis"; the correct N. meningitidis is used here.