Mystery Salmonella Outbreak Spreads Rapidly Across U.S.

The Centers for Disease Control and Prevention (CDC) is searching for the source of a Salmonella outbreak that has infected at least 212 people across 23 states and led to 31 confirmed hospitalizations. The onset of illnesses reported so far occurred between June 19 and July 11. No deaths have been attributed to the outbreak.

In the U.S., Salmonella bacteria causes about 1.35 million infections, 26,500 hospitalizations and 420 deaths annually, the CDC estimates. Food is the most common source for these illnesses. The current outbreak is tied to the Salmonella Newport strain of the bacteria, one of more than 2,000 known strains.

“Salmonella is present in the intestines of many animals, so in meat products most outbreaks are caused by fecal contamination,” says John Gibbons, an assistant professor in the University of Massachusetts Amherst’s Department of Food Science. “For fruits and vegetables, Salmonella contamination typically occurs due to poor agricultural practices including the usage of improperly treated manure, contaminated irrigation water, food handlers don’t wash hands, etc.”

Improper storage or transportation at high temperatures can trigger bacteria growth, says Gibbons, so contamination can occur or worsen at various points along the supply chain. Washing produce and cooking meats to proper temperatures can kill the bacteria and prevent infections.

“In recent years S. Newport has become increasingly associated with cattle, in particular culled dairy cattle,” says Ronald Labbe, professor emeritus of food microbiology at University of Massachusetts Amherst. “So raw hamburger would be a likely source.”

In May, the strain was linked to an outbreak involving cheese made from raw goat’s milk, “so there’s another possible ‘vehicle.’ These products are marketed regionally, so it’s no surprise that more than one state is involved,” Labbe said.

Symptoms of an Infection

Most people who get salmonellosis, the intestinal infection caused by the bacteria, experience diarrhea, fever and stomach cramps. In severe cases, the infection can spread to the urine, blood, bones, joints, spinal fluid or brain. Symptoms usually begin six hours to six days after infection and last up to seven days. However, in some instances, symptoms appear weeks after infection or symptoms persist for weeks, according to the CDC.

An infection is diagnosed with a lab test that looks for the bacteria in a person’s stool, body tissue or fluids. Although most people can recover without antibiotics, an antibiotic is recommended for anyone with a severe illness. Antibiotics are also recommended for infected adults over 65 (or over 50 if an underlying condition such as heart disease is present), infants and those with weakened immune systems. The CDC’s initial analysis of bacteria samples from the current outbreak does not indicate any antibiotic resistance.

“Older adults can have more serious symptoms because their immune systems are typically weaker,” says Gibbons. “Older adults are also at higher risk of having the infection spread to other organs.”

State and local public health officials are currently interviewing those infected to determine what they ate and other exposures they may have had in the week before their illnesses started. The CDC is asking anyone experiencing symptoms of a Salmonella infection to contact the local health department. In the meantime, since the source of the outbreak is still unknown the CDC is not recommending consumers avoid any particular foods, restaurant chains or grocery retailers.

“Within the last couple years in the USA, Salmonella outbreaks have come from cut fruit, tahini, breakfast cereal, papaya, egg shells, turkey, melon, etc.,” says Gibbons. “It will take some epidemiological detective work to figure out this outbreak, but public health officials are very good at this.”