DRUG-RESISTANT SALMONELLA INFECTIONS INCREASING, STUDY SAYS

Infections from a strain of the intestinal bug salmonella that can be killed only by "last-ditch" antibiotics are rapidly increasing, warns a new government report.

The study blames widespread use of antibiotics in raising livestock for the development.

Prevalence of the resistant strain, which can neutralize five common antibiotics, grew from less than 1 percent of samples tested in 1979 and 1980 to 34 percent in 1996, says the report from the US Centers for Diseas e Control and Prevention.

While most of the millions of salmonella infections each year are not serious, up to 10 percent can result in life-threatening bloodstream infections for which "our treatment options are limited" when they are caused by the resistant strains, said Dr. M. Kathleen Glynn, a CDC scientist and lead author of the report in the New England Journal of Medicine.

Further, those options "can become even more limited," she said in an interview, referring to the emergence of salmonella in Britain that are resistant to additional antibiotics.

Bacteria can develop resistance to drugs they are frequently exposed to, by random mutations some of which allow the microbes to survive. The salmonella strain described today, called Salmonella enterica subtype typhimurium DT104, is resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline.

While it adds to the increasing worries about antibiotic resistance among disease-causing bugs, the report carries no immediate significance for the public. There is no evidence so far that infections caused by the resistant Salmonella strain are any worse than others, said Glynn.

But she said the emergence of the resistant strain "makes it clear that we need more prudent use of antimicrobial agents in farm animals" and better disease prevention on farms "to slow the emergence of resistance in this and other strains of salmonella."

Salmonella bacteria commonly infect animals and poultry, and people can contract infections from contaminated raw meat, poultry, eggs, water, kitchen surfaces, and utensils. They can also be passed among children in day-care centers, and from young children to parents through diapers.

Infections generally cause nausea, vomiting, cramps, diarrhea, fever, and headache that last several days. No specific treatment is usually needed.

But in 3 percent to 10 percent of infections, the bacteria invades the bloodstream and can cause life-threatening meningitis, and antibiotics are crucial to treat these cases. The drug-resistant strain can be killed by a class of antibiotics called fluoroquinolones, one of which is ciprofloxacin.

Salmonella that are not vulnerable even to fluoroquinolones have been spotted in the United Kingdom, where those antibiotics are permitted in animal husbandry, said the report.

Dr. Bela Matyas, medical director in the epidemiology section of the state Department of Public Health, said "several dozen cases a year" of serious salmonella infections occur in Massachusetts, usually in older, sick people and occasionally in in fants, causing a handful of deaths.

The emergence of the resistant strain "is definitely a concern, mainly for people who are hospitalized" with serious infections, because their treatment becomes more complicated.

Antibiotics are added to animal feed as growth promoters and are also used to treat infections in livestock and poultry. Concern has been growing that routine use of the drugs fosters the emergence of resistant bugs that can be transmitted to consumers.

Dr. Stuart B. Levy of Tufts University School of Medicine, a leading specialist on antibiotic resistance, wrote in an editorial accompanying the CDC report that over 40 percent of the 50 million pounds of antibiotics produced in the United States are used in animals. Levy wrote that antibiotics should be given to animals only to prevent or treat disease, and "in a way that does not perpetuate the selection of resistance."
Publication Date : 1998-05-07 

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