Science Students End Up in ER After Classroom Bacteria Mix-Up

A routine college microbiology class in Utah turned into a public health scare after every student group in the lab misidentified a harmless bacterium as a deadly, meningitis-causing pathogen, prompting 32 people to begin preventive antibiotics.

According to a case report published in the CDC's Morbidity and Mortality Weekly Report, the 2025 incident began as a standard laboratory exercise in which students were asked to identify an unknown bacterial sample using biochemical tests and morphological characteristics, without being told beforehand what it actually was. The sample was Plesiomonas shigelloides, a common, largely harmless bacterium found in the environment and even in the gastrointestinal tracts of healthy people.

Every group in the class instead identified the sample as Neisseria meningitidis, a dangerous bacterium that can cause meningitis and bloodstream infections, and can spread through the air. Lab instructors reviewed the students' reasoning and found no obvious errors in their conclusions: the sample had presented as a diplococcus that tested positive for both oxidase and catalase, with carbohydrate fermentation patterns consistent with N. meningitidis.

A Scramble to Respond

Believing there had been a real exposure, health officials launched an emergency response. Of the 33 students, faculty and lab staff potentially exposed, 32 began a 10-day course of preventive antibiotics as a precaution. Because N. meningitidis can spread through respiratory droplets, proper handling calls for masks and enclosed biosafety cabinets in addition to gloves and lab coats. The class had only used gloves and lab coats, with no masks or respiratory protection, raising further concern about the scope of potential exposure.

Two of the exposed individuals developed headaches severe enough to send them to the emergency room, where they underwent spinal taps to rule out meningococcal disease.

The Real Culprit

State public health investigators ultimately determined the actual bacterium used in the exercise was Neisseria sicca, a close relative of N. meningitidis that behaves similarly under laboratory testing but is not considered a serious health threat. The mix-up meant the antibiotics, hospital visits and spinal taps had all been unnecessary, though officials noted the response was reasonable given the information available to instructors and health officials at the time.

The CDC's report highlighted the incident as a reminder for academic laboratories to use extra caution and proper safety protocols when working with unknown biological samples, given how easily even trained laboratory personnel can misidentify closely related bacterial species.

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