Massachusetts Tackles Listeria and Other Foodborne Bacteria Through Teamwork

Increased four-fold

the percentage of Listeria isolates uploaded and reported by Massachusetts to national surveillance systems during 2007–2011

effectively with laboratory, epidemiology, and environmental health professionals to respond quickly to outbreaks

state regulations to make reporting of Listeria isolates required instead of voluntary

food laboratory capacity to support increased food sample testing at the state laboratory

Unpasteurized (raw) milk and cheeses made from raw milk can be contaminated with bacteria that cause serious illness or death. These bacteria include Brucella, Campylobacter, Listeria, Mycobacterium bovis, Salmonella, Shiga toxin-producing Escherichia coli, Shigella, Streptococcus pyogenes, and Yersinia enterocolitica.

Listeria monocytogenes is the third leading cause of death from food poisoning. At least 90% of people who get Listeria infection are pregnant women and their newborns, people aged 65 years or older, or people with weakened immune systems. Most require hospitalization, and about 1 in 5 dies.

Listeria is a hardy germ that can grow on refrigerated foods and be found on equipment and appliances where food is processed and prepared. Pasteurization eliminates Listeria, but contamination can occur after pasteurization.

The Massachusetts Department of Public Health (MDPH)External meets the challenge of foodborne illness through teamwork by bringing together experts in laboratory science, environmental health, and epidemiology in the Working Group on Foodborne Illness Control, established in 1986. This teamwork was tested in 2007 when Massachusetts identified a deadly Listeria outbreak that sickened five people, killed three, and caused one miscarriage. At the time, this was only the third report of a US outbreak of Listeria infection linked to pasteurized milk. Because such outbreaks are so uncommon and most cases likely go undetected, this outbreak could have grown if not for the coordinated efforts of MDPH.

What We Did

In June 2007, MDPH’s State Laboratory Institute used pulsed-field gel electrophoresis (PFGE) to identify the “DNA fingerprint” of a novel strain of Listeria monocytogenes in a patient with listeriosis. This strain had neither been previously identified in Massachusetts nor detected by PulseNet. PulseNet is a national network of public health and regulatory laboratories that submit results of PFGE subtyping (the bacterial DNA fingerprints) to a central database where isolates can be compared across states. The state laboratory staff looked for identical matches of the novel Listeria strain and identified it in three additional Massachusetts patients. Using questionnaires developed for the Listeria InitiativeCdc-pdf, MDPH epidemiologists identified pasteurized milk from a local Massachusetts dairy as a possible source of contamination. A sample of milk provided by one patient confirmed the milk was indeed contaminated with the same strain. This finding directed investigators to the outbreak’s source—a local dairy.

Environmental experts from MDPH’s Food Protection ProgramExternal conducted a full environmental inspection, which included milk sampling of the local dairy plant. This led to a voluntarily closure of the facility and recall of its dairy products. The team then collected more than 100 additional milk samples and environmental swabs for testing, including swabs from two floor drains and one from the bottle washer. The state laboratory detected the outbreak Listeria strain in eight milk samples and one swab from the floor drain. It was concluded that since records indicated that pasteurization methods at the dairy were adequate, contamination of the product likely occurred after pasteurization.

On February 1, 2008, the milk processing facility was permanently closed.

What We Accomplished

Massachusetts’ quick detection, coordinated approach, and thorough response saved lives. This unusual Listeria outbreak is one example of teamwork used to tackle food-related emergencies. To continue the fight against foodborne illnesses, MDPH has also

  • Enhanced food laboratory capacity at the state level
  • Expanded emphasis on food testing within Massachusetts
  • Changed state regulations to require clinical laboratories throughout Massachusetts to submit all Listeria isolates to the state laboratory for PFGE testing
  • Increased the number of food samples submitted for state laboratory testing three-fold from nearly 100 specimens to 300 specimens annually
  • Increased the percentage of Listeria isolates uploaded and cases reported to national surveillance systems four-fold during 2007–2011

Publication date: 07/15/2013

More Information
For story information, contact
Massachusetts Department of Public Health
Division of Epidemiology and Immunization
Melissa A. Cumming M.S.
Epidemiologist-Zoonotic Project Coordinator
(W, F) West Boylston Office 508-792-7880 ext. 2345
For product information, contact
Centers for Disease Control and Prevention
1600 Clifton Road NE, Atlanta, GA 30333

The information in Public Health Practice Stories from the Field was provided by organizations external to CDC. Provision of this information by CDC is for informational purposes only and does not constitute an endorsement or recommendation by the US government or CDC.

Page last reviewed: October 5, 2018