Notes from the Field: False-Positive Measles Test — Maine, February 2012

On February 7, 2012, the Maine Center for Disease Control and Prevention was notified of suspected measles infection in an unvaccinated woman aged 57 years. The patient went to her medical provider on January 30 after 3 days of headache and fever and 2 days of papular rash. The rash began on her neck and spread to her abdomen, legs, and back. Two days later she developed coryza and cough. The rash resolved by February 6. A serum specimen collected on January 31 demonstrated a high titer of measles immunoglobulin M (IgM) and was positive for measles immunoglobulin G (IgG) on testing at a reference laboratory.

An epidemiologic investigation conducted after initial laboratory testing did not find a likely source of measles exposure. The patient reported a history of measles in childhood. Of note, 1–2 weeks before illness onset she was exposed to her grandson, who had parvovirus infection. Serum and nasopharyngeal swabs were collected on February 7 for repeat testing at the Maine Health and Environmental Testing Laboratory. Direct-capture measles IgM and polymerase chain reaction test results were negative at the state laboratory. After learning of the patient's parvovirus exposure and with the knowledge that some measles IgM testing had provided false-positive results (1), the Maine Center for Disease Control and Prevention requested parvovirus testing of the original serum specimen at the reference laboratory. Parvovirus testing demonstrated a high titer of parvovirus IgM but was negative for parvovirus IgG, consistent with recent infection.

This case highlights the importance of careful epidemiologic investigation to guide appropriate laboratory testing and the crucial role of state public health laboratories in confirming or ruling out infectious diseases of public health concern. In this investigation, the history of measles infection in childhood, lack of a recent likely source of measles exposure, and recent exposure to parvovirus made measles a less likely cause of illness, despite the initial reference laboratory test results. The state laboratory was able to perform a direct-capture IgM test quickly and rule out measles, eliminating the need for an intense and costly public health response. Parvovirus should be considered in the differential diagnosis of acute febrile rash illness, even in the setting of positive measles IgM, when clinical information is compatible and epidemiologic investigation suggests low probability of measles infection.

Reported by

Ann Farmer, MS, Vicki Rea, MPH, Stephen D. Sears, MD, Brian Bernier, MPH, Maine Dept of Health and Human Svcs. Susan E. Manning, MD, Career Epidemiology Field Officer Program, Office of Public Health Preparedness and Response, CDC. Corresponding contributor: Ann Farmer, ann.farmer@maine.gov, 207-287-3600.

Reference

1. Alaska Department of Health and Social Services. False positive laboratory test results for measles—some disease actually parvovirus B19. In: Epidemiology Bulletin. Anchorage, AK: Alaska Department of Health and Social Services; 1994. Available at http://www.epi.hss.state.ak.us/bulletins/docs/b1994_26.htm. Accessed May 25, 2012.