Vital signs: Listeria illnesses, deaths, and outbreaks--United States, 2009-2011.

BACKGROUND: Older adults, pregnant women, and persons with immunocompromising conditions are at higher risk than others for invasive Listeria monocytogenes infection (listeriosis), a rare and preventable foodborne illness that can cause bacteremia, meningitis, fetal loss, and death.

METHODS: This report summarizes data on 2009-2011 listeriosis cases and outbreaks reported to U.S. surveillance systems. The Listeria Initiative and PulseNet conduct nationwide surveillance to rapidly detect and respond to outbreaks, the Foodborne Diseases Active Surveillance Network (FoodNet) conducts active, sentinel population-based surveillance to track incidence trends, and the Foodborne Disease Outbreak Surveillance System (FDOSS) receives reports of investigated outbreaks to track foods and settings associated with outbreaks.

RESULTS: Nationwide, 1,651 cases of listeriosis occurring during 2009-2011 were reported. The case-fatality rate was 21%. Most cases occurred among adults aged ≥65 years (950 [58%]), and 14% (227) were pregnancy-associated. At least 74% of nonpregnant patients aged <65 years had an immunocompromising condition, most commonly immunosuppressive therapy or malignancy. The average annual incidence was 0.29 cases per 100,000 population. Compared with the overall population, incidence was markedly higher among adults aged ≥65 years (1.3; relative rate [RR]: 4.4) and pregnant women (3.0; RR: 10.1). Twelve reported outbreaks affected 224 patients in 38 states. Five outbreak investigations implicated soft cheeses made from pasteurized milk that were likely contaminated during cheese-making (four implicated Mexican-style cheese, and one implicated two other types of cheese). Two outbreaks were linked to raw produce.

CONCLUSIONS: Almost all listeriosis occurs in persons in higher-risk groups. Soft cheeses were prominent vehicles, but other foods also caused recent outbreaks. Prevention targeting higher-risk groups and control of Listeria monocytogenes contamination in foods implicated by outbreak investigations will have the greatest impact on reducing the burden of listeriosis.

IMPLICATIONS FOR PUBLIC HEALTH PRACTICE: Careful attention to food safety is especially important to protect vulnerable populations. Surveillance for foodborne infections like listeriosis identifies food safety gaps that can be addressed by industry, regulatory authorities, food preparers, and consumers.