Multistate outbreak of Listeriosis

CDC is collaborating with public health and regulatory officials in several states and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Listeria monocytogenes infections (listeriosis).

Public health investigators are using data from PulseNet, the national subtyping network of state and local public health laboratories, CDC, and federal food regulatory laboratories that performs molecular surveillance of foodborne infections, to identify cases of illness that may be part of this outbreak. The PulseNet data consists of DNA “fingerprints” of Listeria obtained through testing with pulsed-field gel electrophoresis, or PFGE. We are supplementing PFGE data with whole-genome sequencing. The 5 isolates already sequenced are closely related.

A total of 8 persons infected with the outbreak strain of Listeria monocytogenes have been reported from two states. The number of ill people identified in each state is as follows: California (1), Maryland (7).

Among persons for whom information is available, dates that illness was diagnosed range from August 1, 2013 to November 27, 2013. Seven of the eight ill persons were hospitalized. Five of the illnesses were related to a pregnancy; two of these were diagnosed in two mother–newborn pairs, and one in only the newborn. The three other illnesses occurred among adults. One death was reported in California. All ill persons were reported to be of Hispanic ethnicity.

The outbreak can be visually described with a chart showing the number of persons who were diagnosed each day. This chart is called an epidemic curve or epi curve. Clinical specimens that were collected after February 1, 2014 might not be reported yet due to the time it takes between when a person becomes ill and when the illness is reported. This takes an average of 2 to 3 weeks.

About 800 laboratory-confirmed cases of listeriosis are reported each year in the United States, and typically 3 or 4 outbreaks are identified and reported to CDC annually. Some foods that have been linked to outbreaks in recent years include several types of cheeses (Mexican-style cheeses, soft ripened cheeses, and imported ricotta salata cheese), whole cantaloupe, raw sprouts, and precut celery.

Investigation of the Outbreak

In interviews, ill persons answered questions about foods consumed and other exposures in the month before becoming ill. All patients in Maryland reported consuming soft or semi-soft Hispanic-style cheese and all shopped at different locations of same food store chain (Chain A). Testing of cheese products collected from Chain A stores was performed in Maryland and Virginia.

Virginia’s Division of Consolidated Laboratory Services (DCLS) identified the outbreak strain of Listeria monocytogenes in a sample of Caujada en Terron (fresh cheese curd) collected by the Virginia Department of Agriculture and Consumer Services (VDACS) from a Chain A store. This cheese was likely produced by Roos Foods of Kenton, Delaware and was later repackaged in the Chain A store. VDACS issued a press releaseExternal Web Site Icon on February 15, 2014 instructing persons who purchased this product not to consume the cheese and to discard any remaining product.

VDACS subsequently collected pre-packaged Caujada en Terron produced by Roos Foods from Chain A that was not repackaged in the store. The Virginia DCLS identified Listeria monocytogenes from these samples; a consumer advisoryExternal Web Site Icon was issued on February 21, 2014. DNA fingerprinting and whole-genome sequencing will be performed on these isolates. In addition, the Maryland Department of Health and Mental Hygiene has tested samples of pre-packaged cheese products purchased at Chain A stores; those products produced by Roos Foods are preliminarily positive for Listeria monocytogenes. On February 19, 2014, the Maryland Department of Health and Mental Hygiene issued a warning to consumersExternal Web Site Icon to not eat any cheese products made by Roos Foods. Their warning stated that Roos Foods cheese products are sold under brand names Santa Rosa de Lima, Amigo, Mexicana, Suyapa, La Chapina, and La Purisima Crema Nica.

Further investigation is needed to determine the source of the patients’ illnesses, including whether the illnesses were related to food products that tested positive for Listeria.