The New England Journal of Medicine reported an outbreak of fluoroquinolone resistant salmonella infection last week (1). The report raises several important issues – infection control in hospitals and nursing homes, the potential for importation of infection, and caution in the use of antibiotics.
A prolonged outbreak of fluoroquinolone resistant salmonella infection was associated with two nursing homes and a hospital in Portland, Oregon (1). The outbreak came to light in February 1997, when three cases of Salmonella enterica serotype Schwarzengrund infection were linked to a nursing home, where two were current and one was a former resident. Subsequent retesting, interviews with medical staff and reviews of charts and death certificates, and a case control study revealed a larger outbreak. Eleven patients with fluoroquinolone resistant salmonellosis were identified in two nursing homes, nine in one and two in another.
Isolates shared resistance to at least three antimicrobials and had similar pulsed field gel electrophoresis patterns, which were also similar to that of the only previous isolate of S. enterica serotype Schwarzengrund in the United States (isolated in New York in 1995, from a patient who had previously been an inpatient in the Philippines). The nine isolates submitted to polymerase chain reaction of the gyrA gene also shared the same mutations as the 1995 isolate. The index case in this outbreak had also been in the same hospital in the Philippines (transferred to the US in December 1995 and found to be infected two months later.
Spread of infection in the nursing homes is believed to have been from person to person or through contact with infected surfaces. In the case control study four of five cases of salmonellosis compared with two of 13 controls had received fluoroquinolones in the precious six months.
The authors note that the prevalence of fluoroquinolone resistance in nontyphoidal salmonella in the Philippines rose from 2.5% in 1992 and 1993 to 4.7% in 1998. They suggest that the availability of fluoroquinolones over-the-counter and their use in livestock may have contributed to the emergence of resistance in the Philippines.