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Infectious Diseases in Obstetrics and Gynecology
Volume 2015, Article ID 201479, 5 pages
Research Article

Estimating the Attack Rate of Pregnancy-Associated Listeriosis during a Large Outbreak

1Division of Foodborne, Waterborne, and Environmental Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
2Epidemic Intelligence Service, Scientific Education and Professional Development Program Office, Centers for Disease Control and Prevention, Atlanta, GA 30329, USA
3El Paso County Public Health, Colorado Springs, CO 80907, USA
4Denver Health and Hospital Authority, Denver, CO 80204, USA
5Tri-County Health Department, Greenwood Village, CO 80111, USA
6Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA 30329, USA

Received 8 November 2014; Accepted 27 January 2015

Academic Editor: Anna Wald

Copyright © 2015 Maho Imanishi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background. In 2011, a multistate outbreak of listeriosis linked to contaminated cantaloupes raised concerns that many pregnant women might have been exposed to Listeria monocytogenes. Listeriosis during pregnancy can cause fetal death, premature delivery, and neonatal sepsis and meningitis. Little information is available to guide healthcare providers who care for asymptomatic pregnant women with suspected L. monocytogenes exposure. Methods. We tracked pregnancy-associated listeriosis cases using reportable diseases surveillance and enhanced surveillance for fetal death using vital records and inpatient fetal deaths data in Colorado. We surveyed 1,060 pregnant women about symptoms and exposures. We developed three methods to estimate how many pregnant women in Colorado ate the implicated cantaloupes, and we calculated attack rates. Results. One laboratory-confirmed case of listeriosis was associated with pregnancy. The fetal death rate did not increase significantly compared to preoutbreak periods. Approximately 6,500–12,000 pregnant women in Colorado might have eaten the contaminated cantaloupes, an attack rate of ~1 per 10,000 exposed pregnant women. Conclusions. Despite many exposures, the risk of pregnancy-associated listeriosis was low. Our methods for estimating attack rates may help during future outbreaks and product recalls. Our findings offer relevant considerations for management of asymptomatic pregnant women with possible L. monocytogenes exposure.