Colorado’s Public Health Laboratory: A Leader in Detecting Listeria and Other Foodborne Bacteria


with one of the highest sample submission rates in the country—even though sample submission is voluntary

efficient laboratories and trains scientists for food-related emergencies

rapidly and strategically to combat threats to Colorado’s food supply

food safety surveillance, research, and training with local, state, and national partners

Listeria monocytogenes are deadly bacteria commonly found in the environment. Listeriosis, a rare disease caused by these bacteria, occurs when someone eats food contaminated with Listeria. Listeriosis is difficult to recognize and only diagnosed by laboratory testing.

The health and economic costs of listeriosis are staggering. At least 90% of people diagnosed with listeriosis are newborns, pregnant women and their fetuses, people over 65 years of age, and those with weakened immune systems. Most patients with listeriosis require hospital care, and one in five listeriosis cases results in death or fetal loss. The annual cost of listeriosis is estimated to be $2.6 billion, according to a 2012 article in the Journal of Food Protection. This includes medical costs, productivity loss, cost of premature death, and disability.

The Colorado Department of Public Health and Environment (CDPHE) is a leader in detecting and characterizing strains of Listeria and other foodborne bacteria. The high rate of isolate submission by hospital and clinical laboratories for further testing helps CDPHE track and respond rapidly to outbreaks. In recent years, CDPHE identified Escherichia coli O157 contamination in spinach and Salmonella in peanut butter and jalapeno peppers.

This well-honed laboratory capacity prepared CDPHE to detect one of the deadliest foodborne outbreaks in the United States—an outbreak of listeriosis linked to cantaloupe consumption. The outbreak spanned 28 states, sickened 147 people, killed 33, and resulted in one miscarriage. Eventually traced to a single cantaloupe farm, the outbreak would have taken more lives if not for the laboratory’s quick action.


What We Did

In late August 2011, CDPHE received reports from clinicians of seven Listeria infections in Colorado. Seven cases represented a large spike for Colorado—up from a monthly average of two cases—and would soon signal that a national outbreak was underway. The Listeria isolates from patients were immediately DNA “fingerprinted” at CDPHE’s public health laboratory for PulseNet. PulseNet is a national network of public health laboratories that submit results of molecular subtyping (the bacterial DNA fingerprints) to a central database where isolates can be identified and matched between states. By September 7, CDC launched a multistate investigation because the same outbreak strain of Listeria identified by CDPHE was causing illness in patients in other states.

To identify an outbreak source, the same outbreak strain needs to be found in food. Early in the investigation, interviews of patients suggested that cantaloupe might be that source. After collecting cantaloupe samples from patients’ homes, grocery stores, and the implicated farm, CDPHE microbiologists trained themselves to test for and detect Listeria in cantaloupe.

On September 14, just seven days after the outbreak’s detection, the farm issued a voluntary recall of its cantaloupe.

What We Accomplished

Colorado’s quick detection and response saved lives. CDPHE coordinated its laboratory work with epidemiologists and environmental specialists nationally and locally to help identify the contaminated food source, alert the public, and protect the national food supply. The multistate listeriosis outbreak of 2011 is one example of public health agencies responding rapidly to food-related emergencies to prevent further illness.

To continue the fight against foodborne illnesses, CDPHE is—

  • Enhancing food safety surveillance, research, and training by participating in such networks as the Integrated Food Safety Centers of Excellence and the Foodborne Diseases Active Surveillance Network (FoodNet)
  • Maintaining one of the highest national sample submission rates, even though sample submission to the state laboratory is voluntary
  • Participating in the Food Emergency Response Network, which screens for radioactive material in food, water, and soil, as well as in humans who may have been exposed to radioactive material

Publication date: 07/05/2013

More Information
For story information, contact
Colorado Department of Public Health and Environment
Laboratory Services Division
Hugh Maguire, PhD
Program Manager, Microbiology
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