Clinical Impact of Antibiotic-Resistant Salmonella

Antibiotic-Resistant Salmonella

Hello. My name is Dr. Christopher Braden. I am the Director of the Division of Foodborne, Waterborne, and Environmental Diseases at CDC. Today I will be speaking about infections with antibiotic-resistant Salmonella. I will not be speaking of Salmonella Typhi, the agent of typhoid fever. Rather, I will describe the clinical impact of the types of nontyphoidal Salmonella, often foodborne, that are common in the United States and increasingly associated with antibiotic resistance. In a recent report by CDC, titled Antibiotic Resistance Threats in the United States, 2013, drug-resistant, nontyphoidal Salmonella was listed among bacteria that pose a serious threat level.

Nontyphoidal Salmonella causes approximately 1.2 million illnesses, 23,000 hospitalizations, and 450 deaths each year in the United States. Direct medical costs are estimated to be $365 million annually. Of concern, surveillance data reveal that an increasing proportion of nontyphoidal Salmonella are resistant to ceftriaxone or ciprofloxacin, drugs representing classes of antibiotics commonly used to treat severe salmonellosis. Currently, CDC is seeing resistance to ceftriaxone in about 3% of nontyphoidal Salmonella tested, and some level of resistance to ciprofloxacin in about 3%. Taking into account all of the classes of antibiotics for which testing is done at CDC, about 5% of nontyphoidal Salmonella tested by CDC are resistant to antibiotics in 5 or more classes.

Multiple outbreaks of foodborne salmonellosis have occurred in which the Salmonella organisms were multidrug resistant. For example, in 2011 an outbreak due to Salmonella Typhimurium linked to ground beef involved 20 people primarily in northeast states; this pathogen was resistant to antibiotics in multiple classes, including aminoglycosides, tetracyclines, sulfonamides, and beta lactams, and cephalosporins and beta lactams in combination with beta-lactamase inhibitors. This pattern of resistance is often associated with co-located resistance genes on a bacterial plasmid, which is a mobile genetic element able to transfer to other types of bacteria.