Investigation Details

Posted July 23, 2021

July 23, 2021

Epidemiologic and laboratory data show that contact with backyard poultry is making people sick.

Since the last update on June 24, 2021, one additional serotype (Salmonella Muenchen) and 198 more illnesses have been added to this outbreak investigation.

Epidemiologic Data

As of July 23, 2021, a total of 672 people infected with one of the outbreak strains have been reported from 47 states (see map). Illnesses started on dates ranging from December 15, 2020, to June 25, 2021 (see timeline).

Age information was available for 670 people. Their ages range from less than 1 to 97 years, with a median age of 34 years, and 181 (27%) are young children under 5 years. Of 657 people with sex information available, 385 (59%) are female. Of 489 people with information available, 157 (32%) have been hospitalized. Two deaths have been reported, one from Indiana and one from Virginia.

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 came into contact with the week before they got sick. Of the 423 people interviewed, 292 (69%) reported contact with backyard poultry before getting sick.

Laboratory Data

On June 15, public health officials in Maryland collected samples from a sick person’s chickens for testing. WGS showed that the Salmonella Enteritidis found in one of the chicken’s samples matched an outbreak strain.

WGS was also used to identify any predicted antibiotic resistance for bacteria from 544 sick people’s samples, 3 animal samples, and 7 environmental samples. Of the 554 samples, 209 (38%) were predicted to be resistant to one or more of the following antibiotics: amoxicillin-clavulanic acid (1.1%), ampicillin (1.3%), chloramphenicol (0.5%), cefoxitin (1.1%), ceftriaxone (1.1%), ciprofloxacin (0.2%), gentamicin (2.2%), kanamycin (0.4%), streptomycin (35.4%), sulfamethoxazole (2.9%), and tetracycline (33.9%). CDC’s National Antimicrobial Resistance Monitoring System (NARMS) laboratory is currently conducting standard antibiotic susceptibility testing.

Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed, some illnesses in these outbreaks may be difficult to treat with some commonly recommended antibiotics and may require a different antibiotic choice.

Previous Updates

Epidemiologic and laboratory data show that contact with backyard poultry is making people sick.

Since the last update on May 20, 2021, one additional serotype (Salmonella Mbandaka) and 311 more illnesses have been added to this outbreak investigation.

Epidemiologic Data

As of June 17, 2021, a total of 474 people infected with one of the outbreak strains have been reported from 46 states (see map). Illnesses started on dates ranging from December 15, 2020, to June 4, 2021 (see timeline).

Age information was available for 471 people. Their ages range from less than 1 to 97 years, with a median age of 31 years, and 139 (30%) are young children under 5 years. Of 466 people with sex information available, 269 (58%) are female. Of 334 people with information available, 103 (31%) have been hospitalized. One death has been reported from Indiana.

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 came into contact with the week before they got sick. Of the 271 people interviewed, 209 (77%) reported contact with backyard poultry before getting sick.

Laboratory Data

On May 7, local public health officials in California collected samples from a sick person’s duck environment for testing. Whole genome sequencing (WGS) showed that the Salmonella Hadar found on the ground and in the duck’s poop and sleeping area match the outbreak strain.

On June 1, public health officials in Arizona collected samples from a sick person’s chickens and the chicken environment for testing. WGS showed that the Salmonella Hadar found on chickens, their roost, and a water source match the outbreak strain.

WGS was also used to identify any predicted antibiotic resistance for bacteria from 382 sick people’s samples, 1 animal sample, and 9 environmental samples. Of the 392 samples, 159 (41%) were predicted to be resistant to one or more of the following antibiotics: amoxicillin-clavulanic acid (1.0%), ampicillin (1.3%), chloramphenicol (0.5%), cefoxitin (1.0%), ceftriaxone (1.0%), ciprofloxacin (0.3%), streptomycin (38.5%), sulfamethoxazole (2.3%), tetracycline (37.2%), gentamicin (1.5%), and Kanamycin (0.5%). CDC’s National Antimicrobial Resistance Monitoring System (NARMS) laboratory is currently conducting standard antibiotic susceptibility testing.

Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed, some illnesses in this outbreak may be difficult to treat with some commonly recommended antibiotics and may require a different antibiotic choice.

CDC and public health officials in many states are collecting different types of data to investigate multistate outbreaks of Salmonella infections with serotypes Enteritidis, Hadar, and Infantis.

Epidemiologic and laboratory data show that contact with backyard poultry is making people sick.

Epidemiologic Data

As of May 20, 2021, a total of 163 people infected with one of the outbreak strains have been reported from 43 states (see map). Illnesses started on dates ranging from February 12, 2021, to April 25, 2021 (see timeline).

Sick people range in age from less than 1 to 87 years, with a median age of 24 years, and 58% are female. Of 109 people with information available, 34 (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 2 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 came into contact with in the week before they got sick. Of the 92 people interviewed, 81 (88%) reported contact with backyard poultry before getting sick.

Laboratory Data

Public health investigators are using the PulseNet system to identify illnesses that may be part of this outbreak. 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 this outbreak likely got sick from the same type of animal.

On April 15, public health officials in Ohio collected samples from a sick person’s ducklings for testing. WGS showed that the bacteria, Salmonella serotype Hadar, in duckling poop are closely related to bacteria from sick people. This means that people likely got sick from contact with backyard poultry.

WGS was also used to identify any predicted antibiotic resistance. Among bacteria from 125 sick people’s samples and 1 animal sample, 63 (50%) were predicted to be resistant to one or more of the following antibiotics: ampicillin (1%), chloramphenicol (1%), streptomycin (50%), sulfamethoxazole (2%), and tetracycline (48%). CDC’s National Antimicrobial Resistance Monitoring System (NARMS) laboratory is currently conducting standard antibiotic susceptibility testing. Most people with Salmonella illness recover without antibiotics. However, if antibiotics are needed to treat people in this outbreak with severe illnesses, this resistance is unlikely to affect the choice of antibiotic.