CDC Investigating Multi-State Outbreak of Human Salmonella Cotham

The Centers for Disease Control and Prevention (CDC) is collaborating with public health, veterinary, and agriculture officials in many states and the U.S. Department of Agriculture National Veterinary Services LaboratoriesExternal Web Site Icon (NVSL) to investigate an outbreak of Salmonella Cotham infections linked to contact with pet bearded dragons purchased from multiple stores in different states. Bearded dragons are popular pet lizards, native to Australia, that come in a variety of colors. Public health investigators are using the PulseNet system to identify cases of illness that may be part of this outbreak. PulseNet, the national subtyping network of public health and food regulatory agency laboratories coordinated by the CDC, obtains DNA "fingerprints" of Salmonella bacteria through diagnostic testing with pulsed-field gel electrophoresis (PFGE).

On Jan. 22, 2014, CDC was notified by the Wisconsin Department of Health Services of a cluster of Salmonella Cotham infections with a high proportion of ill persons reporting exposure to pet reptiles. Since 2012, there have been 12 ill persons infected with Salmonella Cotham in Wisconsin, and 10 (83%) of 12 persons reported contact with pet bearded dragons. Wisconsin receives funding under the the CDC FoodCORE (Foodborne Diseases Centers for Outbreak Response Enhancement) program. These centers work together to develop new and better methods to detect, investigate, respond to, and control multistate outbreaks of foodborne diseases.

Salmonella Cotham is a rare serotype. Searching historical Salmonella databases, the CDC determined that Salmonella Cotham represents only 0.01% of all human isolates in the United States since 1963. Before this outbreak, typically fewer than 25 Salmonella Cotham infections were reported to PulseNet annually. Given the rarity of the Cotham serotype and the information gathered by Wisconsin, the CDC conducted a search of PulseNet for all Salmonella Cotham infections reported since 2012.

As of April 21, 2014, a total of 132 persons infected with the outbreak strain of Salmonella Cotham have been reported from 31 states since February 21, 2012. The number of ill persons identified in each state is as follows (listed in alphabetical order): Arizona (4), California (21), Colorado (2), Florida (3), Georgia (1), Idaho (3), Illinois (6), Kansas (6), Kentucky (4), Maryland (3), Massachusetts (1), Michigan (5), Minnesota (3), Missouri (7), Nebraska (1), Nevada (3), New Hampshire (1), New Jersey (3), New York (10), North Carolina (2), Ohio (1), Oregon (2), Pennsylvania (5), South Carolina (1), South Dakota (1), Tennessee (5), Texas (6), Utah (3), Virginia (3), Washington (4), and Wisconsin (12).

Among 132 persons for whom information is available, dates that illnesses began range from February 20, 2012 to April 1, 2014. Ill persons range in age from less than 1 year to 79 years, with a median age of 2 years. Fifty-eight percent of ill persons are children 5 years of age or younger. Fifty-one percent of ill persons are female. Among 67 ill persons with available information, 28 (42%) have been hospitalized. No deaths have been reported.

This outbreak can be visually described with a chart showing the number of persons who became ill each day. This chart is called an epidemic curve (epi curve). Illnesses that occurred after March 22, 2014 might not yet be reported 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 4 weeks. Please see the Timeline for Reporting Cases of Salmonella Infection for more details.

Epidemiologic, laboratory, and traceback investigations conducted by officials in local, state, and federal public health agencies indicate that contact with pet bearded dragons is the likely source of this outbreak of Salmonella Cotham infections.

On March 25, 2014, CDC sent a questionnaire to the states involved in the investigation to obtain more detailed information from ill persons about recent contact with reptiles. In interviews, ill persons answered questions about contact with animals and foods consumed during the week before becoming ill. To date, CDC has received a total of 31 completed questionnaires. Twenty-seven (87%) of 31 persons interviewed reported contact with reptiles or their environments before becoming ill. When asked about the type of reptile, 25 (81%) of 31 persons reported contact with lizards; of these 25 persons, 21 (84%) specifically reported contact with bearded dragons, a type of lizard. The percentage of ill persons in this outbreak reporting contact with a reptile is substantially higher than the percentage of U.S. households that reported owning a pet reptile in a survey conducted in 2013-2014 by the American Pet Products Association (5.6%). State and local health departments are continuing to interview ill persons.

The Oregon State Public Health LaboratoryExternal Web Site Icon has isolated the outbreak strain of Salmonella Cotham from samples from a pet bearded dragon and its habitat collected from an ill person’s home in Oregon.

The National Antimicrobial Resistance Monitoring SystemExternal Web Site Icon (NARMS) is a U.S. public health surveillance system that tracks antibiotic resistance in foodborne and other enteric bacteria found in people, raw meat and poultry, and food-producing animals.  NARMS is an interagency partnership among CDC, the U.S. Food and Drug Administration (FDA), the U.S. Department of Agriculture (USDA), and state and local health departments.

The NARMS human surveillance program at CDC monitors antibiotic resistance in Salmonella and several other bacteria isolated from clinical specimens and submitted to NARMS by public health laboratories.  CDC's NARMS laboratory tested Salmonella Cotham isolates collected from three ill persons infected with the outbreak strain. One (33%) of the three isolates tested was multidrug resistant (defined as resistance to at least one antibiotic in three or more antibiotic classes), and the other two (67%) isolates tested were pansusceptible (susceptible to all antibiotics tested). The multidrug resistant isolate has shown resistance to the following antibiotics: ampicillin, chloramphenicol, streptomycin, sulfisoxazole, tetracycline, amoxicillin-clavulanic acid, cefoxitin, ceftriaxone, ceftiofur, and gentamicin. One of these antibiotics, ceftriaxone, is commonly used to treat serious Salmonella infections, including those in children. The CDC NARMS laboratory is continuing to conduct antibiotic resistance testing on Salmonella Cotham isolates collected from ill persons. Additional results will be reported when they become available.

The pet industry is working closely with the CDC to determine the source of the bearded dragons linked to this outbreak in order to prevent additional illnesses. Through this collaboration, multiple potential bearded dragon breeders have been identified that supply lizards to pet stores in the United States where ill persons reported purchasing their animals. This investigation is ongoing and CDC will update the public when more information is available.

Source: CDC