Outbreak of Salmonella Newport Infections with Decreased Susceptibility to Azithromycin Linked to Beef Obtained in the United States and Soft Cheese Obtained in Mexico



CDC is concerned about an increase in human illness from a new strain of multidrug-resistant (MDR) Salmonella Newport, that appears to have spread from cattle in the United States and Mexico. A new CDC report highlights an emerging strain of Salmonella Newport; that may not respond to antibiotics recommended for treatment of severe infections. During June 2018–March 2019, CDC identified 255 infections and 60 hospitalizations from 32 U.S. states. Infections were linked to beef obtained in the United States and soft cheese obtained in Mexico, suggesting that this strain could be present in cattle in both countries. Antibiotic susceptibility testing showed that the strain had decreased susceptibility to azithromycin and nonsusceptibility to ciprofloxacin–two commonly prescribed oral antibiotics. This leaves ceftriaxone, an injectable antibiotic, as the recommended treatment option. Most patients with Salmonella infections recover without antibiotics, but those with severe infections need antibiotics. Resistant infections can be harder to treat, and patients may be at increased risk for developing serious complications.

What Clinicians Should Know


In this MDR outbreak, consumption of cheese and beef were both associated with illness, indicating that dairy cattle were a likely source of these infections. 


Whole genome sequencing was valuable in linking human infections to food sources, distinguishing the MDR outbreak strain from an antibiotic-susceptible strain that was causing a simultaneous outbreak; and predicting antibiotic resistance. In this outbreak, one in three patients received an antibiotic that was likely ineffective. 


Clinicians should limit use of antibiotics for patients with an acute diarrheal illness to those with clinical indications, and antibiotic selection should be based on susceptibility results whenever possible. For empiric treatment of patients who need antibiotics and are suspected to have this strain of MDR Newport, clinicians should consider alternatives to ciprofloxacin and azithromycin, such as ceftriaxone.


Please read the MMWR for more information. 


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For information about this update or other clinical issues, or to send your feedback, please contact us at coca@cdc.gov

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