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Emerging Infectious Diseases Conference Roundup
Anthrax, plague, antibiotic-resistant Salmonella, and food safety issues were among topics that participants discussed during the International Conference on Emerging Infectious Diseases (ICEID), held in Atlanta, Ga., during March. Here are selected highlights:
Bacillus anthracis-the bacterium used in the first modern bioterrorist attack in the United States to involve fatalities-was discussed at length in various ICEID sessions, including a late-breaker session on anthrax that was chaired by John Eisold, the attending physician of the Congress of the United States. Vincent Hsu, an emerging infection services officer with the Centers for Disease Control and Prevention (CDC), described how staff workers and emergency workers prevented an anthrax outbreak by responding rapidly to a suspicious letter at the Hart Senate Building. Soon after the letter was opened, tests indicated that it contained a fine powder of Bacillus anthracis. Shortly, a supply of antibiotics was in the hands of 65 office workers. Although the letter contained weapons grade infectious material, no one developed either cutaneous or inhalation anthrax.
Although plague, the infection caused by Yersinia pestis, is generally considered a disease of developing nations, the bacteria that cause it are endemic in parts of the United States. Recently, a 45-year-old camper was admitted to a hospital in Arizona with symptoms of the disease, including fever and purplish lesions and gangrene. When treated with ciprofloxacin, his condition resolved, says Tim Kuberski, a primary care physician at John C. Lincoln Hospital in the Deer Valley area of Phoenix. Ciprofloxacin was used because streptomycin, the standard antimicrobial used for treating cases of plague, was not readily available, and because ciprofloxacin treatment began before a definitive diagnosis was made.
Researchers in charge of the National Antimicrobial Resistance Monitoring System (NARMS) report that three strains-Salmonella enterica serovar Typhimurium R-type ACSSuT, S. enterica serovar Typhimurium R-type AKSSuT, and S. enterica serovar Newport R-type ACSSuT-account for about half the resistant strains in the United States. "Typhimurium is the most common serotype of Salmonella, so the high level of resistance seen is making this a little scary," says Shannon Rossiter, a project coordinator at CDC, which coordinates NARMS. In addition to resistance to the ACSSuT drugs-ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline-about 2% of Salmonella serovar Typhimurium R-type ACSSuT strains are also resistant to ceftriaxone. About 3% of Salmonella serovar Typhimurium R-type AK(kanamycin)SSuT, are resistant to ceftriaxone, and about 71% of Salmonella serovar Newport R-type ACSSuT strains are also resistant to ceftriaxone. Fewer than 1% of the other strains of Salmonella analyzed in the NARMS data are resistant to ceftriaxone.
New York State (NYS) public health researchers are considering prophylactic antibiotics for people who live with or treat patients with infections of invasive group A streptococci-widely called the "flesh-eating bacteria." They are responding to a case in which the invasive form of group A strep infection was transmitted from a resident in a group home to a nurse who takes throat swabs from such residents. "We were taken aback by this case," says Stan Kondracki, an epidemiologist with the NYS Department of Health, Albany. Although invasive group A strep typically occurs among individuals with dysfunctioning immune systems, this case involved a 47-year-old nurse who otherwise was in good health. She became infected apparently following exposure to droplets from the patient, a 40-year-old with Down syndrome who died of the infection. Within a day, the nurse developed symptoms of strep infection that led to necrotizing fasciitis, but recovered. Pulsed-field gel electrophoresis showed that the organism that killed the patient was identical to the one that infected the nurse, according to Kondracki. Four other patients at the home were infected with the same strain of strep, were treated with penicillin and rifampin or azithromycin, and none developed the invasive form of the disease, he says.
Seedless, nonorganic green grapes were implicated in a Salmonella outbreak that caused mainly gastrointestinal disease in 41 people across six western states last summer and fall, according to Alicia Cronquist, an epidemic intelligence officer from CDC who was assigned to the Colorado State Health Department. "We were surprised to find that the outbreak of Salmonella enterica serotype Senftenberg-most often found in meats and poultry-was apparently spread to people through grapes," she says. Although investigators were unable to track the outbreak to its origin, sophisticated tests showed that the strain of Salmonella serovar Senftenberg was the same among samples taken from people infected in California, Colorado, Utah, Arizona, Nevada, and New Mexico. Cronquist says that the bacteria may have infected the fruit during harvesting or during months of storage before it was distributed.
Sliced melons-cantaloupes, watermelon and honeydew-were the likely cause of a widespread Salmonella enterica serovar Poona outbreak, according to Kris Carter, a fellow with the California Epidemiologic Investigation Service. Interviews with patients failed to reveal a common food source "until we asked if they had eaten precut melons," she says. For example, all the people who developed symptoms who remembered eating honeydew said they ate precut honeydew. Bacteria on the surface of the melons may infect the fruit when it is cut, and since sliced melon is often served at buffets and sits out for a long time before being eaten, it may provide more opportunities for contaminating bacteria to grow before the fruit is consumed, she points out.
A procedure for keeping lettuce looking fresh might also breed dangerous bacteria. By dipping iceberg lettuce into warm water baths, the vegetable resists brown discoloration, increasing its shelf life. However, the treatment also apparently facilitates growth of Listeria monocytogenes, an organism that can cause serious infections, even when lettuce is stored at refrigeration temperatures, according to Larry Beuchat, research professor of food safety at the University of Georgia, Athens.
Ed Susman is a freelance medical writer from West Palm Beach, Fla.