Investigation Details
Posted July 20, 2023
CDC and public health officials in several states are collecting different types of data to investigate multistate outbreaks of Salmonella infections with serotypes Braenderup, Enteritidis, Indiana, Infantis, Mbandaka, and Typhimurium.
Epidemiologic data show that contact with backyard poultry is making people sick.
Epidemiologic Data
Since the last update on June 15, 280 more illnesses have been reported. As of July 12, a total of 690 people infected with one of the outbreak strains have been reported from 47 states and Puerto Rico (see map). Illnesses started on dates ranging from January 1, 2023, to June 30, 2023 (see timeline). Of 459 people with information available, 141 (31%) have been hospitalized. No deaths have been reported.
The true number of sick people in an outbreak is likely much higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because many people recover without medical care and are not tested for Salmonella. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak.
Public health officials collect many different types of information from sick people, including their age, race, ethnicity, other demographics, and the animals they came into contact with during the week before they got sick. This information provides clues to help investigators identify the source of the outbreak.
The table below has information about sick people in this outbreak (“n” is the number of people with information available for each demographic).
| Demographics | Information |
|---|---|
| Age (n=672) |
Range from 1 month to 92 years Median age of 31 23% under 5 years |
| Sex (n=674) |
57% female 43% male |
| Race (n=455) |
92% White 2% African American/Black 2% Native American or Alaska Native 1% Asian 1% Native Hawaiian or other Pacific Islander 3% reported more than one race |
| Ethnicity (n=438) |
93% non-Hispanic 7% Hispanic |
State and local public health officials are interviewing people about the animals they came into contact with in the week before they got sick. Of the 390 people with information about animal contact, 314 (81%) reported contact with backyard poultry before getting sick. Of 296 people who were asked about eggs from their backyard poultry, 78 (26%) reported eating eggs from their flock.
Laboratory and Traceback Data
Investigators in Michigan, Minnesota, Nevada, Utah, and Wisconsin collected samples from the areas where chicks are housed in stores or at sick people’s homes. Whole genome sequencing (WGS) showed that Salmonella Braenderup, Enteritidis, Mbandaka, and Infantis found in the poultry’s environments are closely related to bacteria from sick people. Poultry that lived in these environments were supplied to stores or poultry owners by at least four different poultry hatcheries.
Of 242 people with information on poultry purchases, 187 (77%) reported purchasing or obtaining poultry after January 1, 2023. Forty-four people reported purchasing poultry from multiple locations. People reported purchasing or obtaining poultry from at least 178 different locations, and 10 people reported purchasing poultry directly from hatcheries online. Investigators are continuing to work with stores and hatcheries that are identified during the investigation to find ways to reduce Salmonella in poultry.
WGS analysis was used to predict resistance to antibiotics for bacteria from 688 people’s samples. Of these, 64 (9%) were predicted to be resistant to one or more of the following antibiotics: amoxicillin-clavulanic acid, ampicillin, cefoxitin, ceftiofur, ceftriaxone, ciprofloxacin, gentamicin, streptomycin, sulfamethoxazole, and tetracycline. Bacteria from the remaining 624 samples had no predicted resistance. Testing of bacteria from 8 sick people’s samples using standard antibiotic susceptibility testing methods by CDC’s National Antimicrobial Resistance Monitoring System (NARMS) largely confirmed these results. Streptomycin and ceftiofur were not tested by this method, and one person’s sample showed resistance to colistin. (NARMS added colistin to the list of drugs tested for Salmonella in 2020; resistance is defined as a minimum inhibitory concentration [MIC] of ≥4 µg/mL. Some Salmonella serotypes may have higher MICs naturally, even without acquired resistance identified.) Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed, this resistance is unlikely to affect the choice of antibiotic used to treat most people.
Public Health Actions
CDC advises everyone to take steps to stay healthy around backyard poultry. CDC and state partners are working with hatcheries and stores that sell poultry to educate new poultry owners and control the spread of Salmonella at hatcheries.
CDC and public health officials in several states are collecting different types of data to investigate multistate outbreaks of Salmonella infections with serotypes Braenderup, Enteritidis, Indiana, Infantis, Mbandaka, and Typhimurium.
Epidemiologic data show that contact with backyard poultry is making people sick.
Epidemiologic Data
Since the last update on May 19, 2023, 306 more illnesses have been reported. As of June 7, 2023, a total of 410 people infected with one of the outbreak strains have been reported from 45 states (see map). Illnesses started on dates ranging from January 1, 2023, to May 25, 2023 (see timeline).
The true number of sick people in an outbreak is likely much higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because many people recover without medical care and are not tested for Salmonella. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak.
Public health officials collect many different types of information from sick people, including their age, race, ethnicity, other demographics, and the animals they came into contact with during the week before they got sick. This information provides clues to help investigators identify the source of the outbreak.
Of 407 people with age information available, sick people range in age from 1 month to 92 years, with a median age of 25 years, and 116 (29%) are children under 5 years of age. Of 398 people with sex information available, 217 people (55%) are female. Of 277 people with race information available, 254 (92%) are White, 7 (2.5%) are African American/Black, 4 (1.4%) are Native American or Alaska Native, 2 (0.7%) are Asian, 2 (0.7%) are Native Hawaiian or other Pacific Islander, and 8 people (2.9%) reported more than one race. Of 268 people with ethnicity information available, 22 (8%) are Hispanic. Of 282 people with hospitalization information available, 84 (30%) have been hospitalized. No deaths have been reported.
State and local public health officials are interviewing people about the animals they came into contact with in the week before they got sick. Of the 232 people with information about animal contact, 187 (81%) reported contact with backyard poultry before getting sick. Of 157 people who were asked about eggs from their backyard poultry, 40 (25%) reported eating eggs from their flock.
Laboratory and Traceback Data
Investigators in Michigan, Minnesota, Utah, and Wisconsin collected samples from the areas where chicks are housed at stores that sell poultry or at sick people’s homes. Whole genome sequencing (WGS) showed that Salmonella Braenderup, Enteritidis, Mbandaka, and Infantis from the animals’ environment are closely related to bacteria from sick people. These poultry were supplied by four different poultry hatcheries.
Of 144 people with information on poultry purchases, 101 (70%) reported purchasing or obtaining poultry after January 1, 2023. Nineteen people reported purchasing poultry from multiple locations. People reported purchasing or obtaining poultry from 109 different locations, and 5 people reported purchasing poultry directly from hatcheries online. Investigators are continuing to work with stores and hatcheries that are identified during the investigation to find ways to reduce Salmonella in poultry.
WGS analysis was used to predict resistance to antibiotics for bacteria from 408 people’s samples and 16 environmental samples. Of the 424 total samples, 33 (8%) were predicted to be resistant to one or more of the following antibiotics: ampicillin, cefoxitin, ceftiofur, ceftriaxone, ciprofloxacin, gentamicin, streptomycin, sulfamethoxazole, tetracycline, and amoxicillin-clavulanic acid. Bacteria from the remaining 391 samples had no predicted resistance. Testing of bacteria from 3 sick people’s samples using standard antibiotic susceptibility testing methods by CDC’s National Antimicrobial Resistance Monitoring System (NARMS) largely confirmed these results. Streptomycin and ceftiofur were not tested by this method, and one person’s sample showed resistance to colistin. (NARMS added colistin to the list of drugs tested for Salmonella. Resistance is defined as a minimum inhibitory concentration (MIC) of at least 4 µg/mL. Some bacteria may have higher MICs naturally, even without acquired resistance identified.) Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed, this resistance is unlikely to affect the choice of antibiotic used to treat most people.
Public Health Action
CDC advises everyone to take steps to stay healthy around backyard poultry. CDC and state partners are working with hatcheries and stores that sell poultry to educate new poultry owners and control the spread of Salmonella at hatcheries.
CDC and public health officials in several states are collecting different types of data to investigate multistate outbreaks of Salmonella infections with serotypes Braenderup, Enteritidis, and Infantis.
Epidemiologic data show that contact with backyard poultry is making people sick.
Epidemiologic Data
As of May 8, 2023, 104 people infected with one of the outbreak strains have been reported from 31 states (see map). Illnesses started on dates ranging from January 1, 2023, to April 20, 2023 (see timeline).
Public health officials collect many different types of information from sick people, including their age, race, ethnicity, other demographics, and the animals they had contact with in the week before they got sick. This information provides clues to help investigators identify the source of the outbreak.
Sick people range in age from 2 months to 83 years, with a median age of 26 years, and 62 people (60%) are female. Of 78 people with race or ethnicity information available, 71 (91%) are White, 2 (2.6%) are African American/Black, 2 (2.6%) are Native American or Alaska Native, and 3 (3.4%) selected Other. Of 84 people with information available, 19 (23%) have been hospitalized. No deaths have been reported.
The true number of sick people in an outbreak is likely much higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because many people recover without medical care and are not tested for Salmonella. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak.
State and local public health officials are interviewing people about the animals they had contact within the week before they got sick. Of the 69 people with information about animal contact, 48 (70%) reported contact with backyard poultry before getting sick. Of 45 people with information available, 10 (22%) reported eating eggs from backyard poultry.
Laboratory Data
Public health investigators are using the PulseNet system to identify illnesses that may be part of these outbreaks. CDC PulseNet manages a national database of DNA fingerprints of bacteria that cause gastrointestinal illnesses. DNA fingerprinting is performed on bacteria using a method called whole genome sequencing (WGS). WGS showed that bacteria from sick people’s samples are closely related genetically. This means that people in these outbreaks likely got sick from the same type of animal.
WGS analysis was used to predict resistance to antibiotics for bacteria from 104 people’s samples and one environmental sample. Of the 105 total samples, 8 (7.6%) were predicted to be resistant to one or more of the following antibiotics: gentamicin, streptomycin, sulfamethoxazole, and tetracycline. Bacteria from the remaining 97 samples had no predicted resistance. Testing of bacteria using standard antibiotic susceptibility testing methods by CDC’s National Antimicrobial Resistance Monitoring System (NARMS) is currently underway. Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed, this resistance is unlikely to affect the choice of antibiotic used to treat most people.
Public Health Action
CDC advises everyone to take steps to stay healthy around backyard poultry. CDC and state partners are working with hatcheries and stores that sell poultry to educate new poultry owners and control the spread of Salmonella at hatcheries.
