Resistant Salmonella causes 6,200 illnesses a year in US

Chris Dall of the Center for Infectious Disease Research Policy reports the U.S. Centers for Disease Control and Prevention (CDC) has published new estimates of the incidence of antibiotic-resistant Salmonella infections in the United States, putting the burden at about 6,200 cases annually.

ab-res-salmIn a report in Emerging Infectious Diseases, CDC researchers estimate the overall incidence of resistant salmonella infections as roughly 2 for 100,000 persons per year from 2004 to 2012They also determined that clinically important resistance was linked to four specific Salmonella serotyopes: Enteritidis, Newport, Typhimurium, and Heidelberg.

Nontyphoidal Salmonella causes an estimated 1.2 million foodborne illnesses and about 450 deaths each year, according to the CDC. While most people who get Salmonella infections recover within a week and do not require antibiotics, more severe infections are generally treated with either ampicillin, ceftriaxone, or ciprofloxacin. Resistance to these drugs can result in increased hospitalization, invasive illnesses, and death.

The new estimates are based on data from the US Census Bureau and from two surveillance systems the CDC uses to track Salmonella and drug-resistant Salmonella: The National Antimicrobial Resistance Monitoring System (NARMS) and the Laboratory-based Enteric Disease Surveillance (LEDS) system. NARMS monitors resistance in Salmonella by testing isolates from infected individuals and determining the percentage of isolates that show resistance. LEDS collects Salmonella surveillance data, including serotypes, from state and territorial public health labs.

The researchers defined three mutually exclusive categories of resistance for the study: ampicillin-only resistance, ceftriaxone/ampicillin resistance, and ciprofloxacin nonsusceptibility.

According to the LEDS data, there were 369,254 culture-confirmed Salmonella infections from 2004 through 2012. Four primary serotypes—Enteritidis, Typhimurium, Newport, and Heidelberg—accounted for 52% of all fully serotyped isolates. NARMS tested 19,410 isolates from 2004 through 2012, and overall resistance was detected in 2,320 isolates. Ampicillin-only resistance was the most common resistance pattern detected, followed by ceftriaxone/ampicillin resistance and ciprofloxacin nonsusceptibility.

Using these data, the researchers determined that from 2004 to 20012 there were approximately 6,200 resistant culture-confirmed infections annually. Overall incidence was 1.93/100,000 person-years for any clinically important resistance, 1.07 for ampicillin-only resistance, .51 for ceftriaxone/ampicillin resistance, and .35 for ciprofloxacin nonsusceptibility.

The authors note that while Enteritidis, Typhimurium, Newport, and Heidelberg account for only half of all culture-confirmed Salmonella infections, the four serotypes accounted for 73% of the Salmonella infections that involved clinically important resistance.

The predominance of these four serotypes, they write, reflects their ability to persist in food animals, be transmitted through the food system, and cause illness. It also suggests that strategies to reduce Salmonella infections caused by these four serotypes could have an impact on the incidence of resistant infections overall.

“The 4 major serotypes that have been driving the incidence of resistant infections should continue to be high priorities in combating resistance,” the authors write.

The report also notes that two of these serotypes—Typhimurium and Newport—have been associated with outbreaks of drug-resistant Salmonella infections linked to contaminated meat, which highlights the need for NARMS to continue monitoring emerging resistance patterns by serotype.

The authors caution, however, that while this estimate of resistant Salmonella infection incidence will help define the magnitude of the problem and guide prevention efforts, it might be telling only part of the story. That’s because it relies on culture-confirmed infections only.

The CDC has estimated that for every culture-confirmed case of Salmonella, there may as many as 29 undetected cases. That could put the annual US incidence as high as 180,000 cases.

Salmonella in Seattle at retail

Poultry have been identified as one of the major sources of salmonellosis, with estimates ranging from 10 to 22% of total cases.

Despite several advances in the industry and new performance standards, the incidence of salmonellosis in the population has not declined over the last 15 years. Salmonella is pervasive in a wide variety of foods, and thus, estimating its burden resulting from specific food categories has been challenging and plagued with uncertainty seattle3due to critical data gaps. The objective of this study was to conduct a year-long market survey (1,322 samples) to help bridge the data gaps on the contamination rates and levels of Salmonella on raw poultry by product type (i.e., breast, thighs, drums, wings, and split breast) and production method (conventional versus organic).

The isolates recovered were serotyped and tested for antibiotic sensitivities. A PCR method was utilized for initial screening of samples after an overnight enrichment in tryptic soy broth. Three-tube most-probable-number (MPN) assays and anti-Salmonella immunomagnetic separation methods were utilized to determine the levels of Salmonella and aid with the recovery of Salmonella species, respectively. Eleven percent of the samples were positive for Salmonella. Significant differences in percent positive rates by product type included up to a 4-fold difference in percent positive rates between establishments, ranging from 7 to 31%.

Of the samples positive for Salmonella species, 94% had <30 MPN/100 g. Production methods identified as organic or as not using antibiotics had significantly higher rates of recovery of Salmonella. On the other hand, all of the Salmonella isolates that were resistant to two or more antibiotics originated from conventional processing establishments where antibiotics were utilized. In addition, a significant proportion of isolates from conventionally processed products were serotypes clinically relevant to humans.

Prevalence, concentrations, and antibiotic sensitivities of Salmonella serovars in poultry from retail establishments in Seattle, Washington

Journal of Food Protection, Number 6, June 2014, pp. 872-1042, pp. 885-893(9)

Mazengia, E., Samadpour, M., Hill, H. W., Greeson, K., Tenney, K., Liao, G., Huang, X., Meschke, J. S.

19 sick in 7 states; update on multistate outbreak of human Salmonella Typhimurium infections linked to ground beef

The U.S. Centers for Disease Control and Prevention reports today that a total of 19 persons infected with the outbreak strain of Salmonella Typhimurium have been reported from 7 states.

The number of ill persons identified in each state is as follows: HI (1), KY (1), MA (1), ME (4), NH (6), NY (5), and VT (1).

Collaborative investigative efforts of state, local, and federal public health and regulatory agencies indicated that this outbreak is linked to eating ground beef purchased from Hannaford Supermarkets.

Contaminated ground beef was recalled from grocery stores but may still be in consumers’ homes.

Consumers should check their homes for recalled products and not eat them; restaurant and food service operators should not serve them.

The full report is available at