The Centers for Disease Control and Prevention (CDC) published a new report on the incidence of antibiotic-resistant Salmonella infections in the United States. Every year, about 6,200 people are sickened with these strains of antibiotic bacteria, but non-resistant Salmonella bacteria cause about 1.2 million illnesses every year in this country.
Salmonella infections are one of the most common types of foodborne illness in this country and around the world. The antibiotics usually used to treat these infections include ceftriaxone, ciprofloxacin, and ampicillin. Unfortunately, antibiotic resistance has been associated with these drugs.
Scientists at the CDC used Bayesian hierarchical models of 2004 – 2012 date from the CDC National Antimicrobial Resistance Monitoring System (NARMS) and Laboratory-based Enteric Disease Surveillance. They based three categories on susceptibility testing: ceftriaxone and ampicillin resistant, ciprofloxacin nonsusceptible but ceftriaxone susceptible, and ampicillin resistant but ceftriaxone and ciprofloxacin susceptible.
They found that the overall incidence of resistant infections was 1.07/100,000 person-years for ampicillin-only resistance, 0.51/100,000 person-years for ceftriaxone and ampicillin resistance, and 0.35/100,000 person-years for ciprofloxacin nonsusceptibility, or ≈6,200 resistant culture-confirmed infections every year.
Antibiotic resistant bacteria pose a serious threat to public health. These infections have been linked to beef, poultry, dairy, eggs, and produce. The four most common serotypes that display antibiotic resistance are Typhimurium, Enteritidis, Newport, and Heidelberg. Those bacteria persist in food animals and are easily transmitted through the food supply.
Serious Salmonella infections are usually treated with third-generation cephalosporins such as ciprofloxacin. Since Salmonella bacteria are becoming resistant to this drug, this is a serious problem.
NARMS monitors resistance among Salmonella bacteria by testing sample of isolates taken from ill persons and determining the percentage that display resistance. During the period of 2004 to 2012, the percentage of ceftriaxone-resistant Salmonella isolates increased from 9% to 22%. The incidence of Heidelberg infections declined from 0.60 to 0.31.
From 2004 to 2012, 48 states reported 369,254 culture-confirmed Salmonella infections. Among those isolates, most were serotyped. Salmonella Enteritidis accounted for 19% of infections; Typhimurium for 18%, Salmonella Newport for 11%, Heidelberg for 4%, and all other serotypes accounted for 48%. So the four primary serotypes accounted for 52% of all infections.
NARMS tested 19,410 isolates and they found resistance in 2,320 of them. The most common resistance pattern was against Ampicillin. The next most common resistance patterns were against ceftriaxone/ampicillin resistance and then against ciprofloxacin.
The overall incidence of resistance was 1.94 per 100,000 person-years for any clinically important resistance, 1.07 for ampicillin-only resistance, 0.51 for ceftriaxone/ampicillin resistance, and 0.35 for ciprofloxacin non susceptibility. Two of the Salmonella serotypes – Typhimurium and Newport – have been linked to actual outbreaks of infections caused by contaminated meat.
The authors do say that, since most cases of Salmonella go unreported, and because this study relied on culture-confirmed cases of salmonellosis, the actual incidence of antibiotic-resistant Salmonella infections could be as high as 180,000 cases instead of the 6,200 estimated.
To prevent Salmonella infections, it’s important to wash your hands before preparing food and before eating. And make sure that you wash fruits and vegetables well before you eat them. All meats, especially ground meats and poultry, should be cooked to a final internal temperature of 165°F and tested with a food thermometer. And make sure you avoid cross-contamination by keeping raw meats and poultry away from foods that are eaten uncooked.