Lymphocytic Choriomeningitis Virus Outbreak and Risk Assessment — Multiple States, 2012

BACKGROUND: Lymphocytic choriomeningitis virus, a rodentborne arenavirus, can cause aseptic meningitis, encephalitis, and severe birth defects among humans. In May 2012, four employees of an Indiana rodent-breeding facility experienced aseptic meningitis caused by lymphocytic choriomeningitis virus. An epidemiologic investigation revealed exposure to lymphocytic choriomeningitis virus infected mice originating from a Kentucky breeding facility (Facility A) as the cause. We investigated Facility A to determine the extent of the outbreak and prevent further cases.

METHODS: We performed lymphocytic choriomeningitis virus serologic testing for all Facility A employees and conducted interviews to assess their infection control practices and potential risk factors for seroconversion. We reviewed shipping records and contacted facilities that had received potentially infected mice to encourage euthanization of the mice and assess employees’ risk for exposure. Pregnant, sick, or immunocompromised pet store employees were offered serologic testing.

RESULTS: Among 32 Facility A employees, 11 (34%) were lymphocytic choriomeningitis virus seropositive, and one experienced aseptic meningitis; the one pregnant employee tested negative. Twenty-nine (91%) reported wearing gloves, and 13 (41%) using a mask. No risk factors were significantly associated with seroconversion. Feeder mice bred as reptile food at Facility A comingled with wild mice, the presumed source of infection. Among facilities from 21 states that received these mice, 264/521 (51%) pet stores and 7/11 (64%) distributors still had >500,000 potentially infected mice, which were subsequently euthanized. Thirty-five pet store employees from six states tested negative for lymphocytic choriomeningitis virus.

CONCLUSIONS: Lymphocytic choriomeningitis virus can pose a serious health risk to persons who work with or handle mice. Rodent breeding facilities should ensure that wild mice are separated from mice intended for distribution. Personal protective equipment and education regarding its use should be provided to employees who handle mice.