In May 2019 the CDC and public health and regulatory officials in several states investigated an outbreak of gastrointestinal illnesses linked to imported raw oysters harvested from Estero El Cardon estuary in Baja, California Sur, Mexico. Sixteen cases were reported by 5 states. Two people were hospitalized. There were no deaths. Illnesses started on dates ranging from December 16, 2018 to April 17, 2019.

Laboratory testing on samples from patients identified multiple pathogens causing infections. Some people were infected with more than one pathogen. Case counts by pathogen or illness: 4 cases of Shigella flexneri infection, 2 cases of Vibrio parahaemolyticus infection, 1 case of Vibrio parahaemolyticus and non-O157 Shiga toxin-producing E. coli, 1 case of Vibrio parahaemolyticus and Shigella flexneri coinfection, 1 case of Shigella flexneri and Campylobacter lari coinfection, 1 case of Vibrio albensis infection, 1 case of norovirus genogroup 1 infection, 1 case of infection with Vibrio of unknown species, and 4 cases of illness without a pathogen identified.

Whole genome sequencing analysis of one Campylobacter lari isolate and five Vibrio parahaemolyticus isolates from ill people predicted resistance to ampicillin. Ampicillin is not a recommended antibiotic for Campylobacter lari or Vibrio parahaemolyticus infections. Analysis of five Shigella flexneri isolates from ill people predicted resistance to ampicillin, chloramphenicol, streptomycin, and tetracycline. These findings are unlikely to affect treatment because other antibiotics are more commonly used until resistance results are available. No resistance was predicted for one STEC isolate from an ill person. Antibiotics are not typically recommended for patients with STEC infections.

On June 21, 2019 the CDC declared the outbreak to be over.

On May 6, 2019 one US distributor of oysters harvested from Estero El Cardon issued a voluntary recall. On May 7, Estero El Cardon was closed to further oyster harvesting pending investigation.