Hands Across the Water: Fluoroquinolone-Resistant Salmonella
Abstract & Commentary
Synopsis: This report describes a nosocomial outbreak of rare fluoroquinolone-resistant Salmonella infection among current or former nursing home residents.
Source: Olsen SJ, et al. A nosocomial outbreak of fluoroquinolone-
resistant Salmonella infection. N Engl J Med. 2001;344:1572-1579.
In 1997, 3 infections due to Salmonella enterica serotype Schwarzengrund were reported to the Oregon state health department. These cases were notable in that all 3 isolates were resistant to fluoroquinolones (rare in the United States), and that all 3 patients were current or former residents of a single nursing home (Nursing Home A). The index patient had been previously hospitalized in the Philippines following a stroke, with subsequent transfer to Nursing Home A. Over a 5-year period, a total of 9 patients admitted to the nursing home were colonized or infected with S enterica serotype Schwarzengrund. An additional 2 cases occurred in a nearby nursing home (Nursing Home B). The link between the 2 facilities appeared to be transmission within a local acute care hospital. A patient residing in Nursing Home B was admitted to the hospital at the same time as a colonized patient from Nursing Home A.
All the Salmonella isolates were closely related based on the results of pulsed-field gel electrophoresis (PFGE). In addition, all shared the same mutations in the gyrA gene responsible for quinolone resistance. In a case-control study, exposure to fluoroquinolones in the prior 6 months was significantly associated with isolation of fluoroquinolone-resistant S enterica serotype Schwarzengrund.
The only prior isolation of fluoroquinolone-resistant Salmonella in the United States occurred in a New York hospital in 1995. It too was serotype Schwarzengrund of the same PFGE type and contained the same gyrA mutations. On further investigation, it was found that the New York patient had been hospitalized in the Philippines in the same hospital as the index patient in Oregon Nursing Home A.
Comment by Robert Muder, MD
This report is notable for a number of reasons. Although outbreaks of Salmonella infection have been previously described in nursing homes, S enterica serotype Schwarzengrund is unusual in the United States and fluoroquinolone resistance among Salmonella isolates is exceedingly rare in this country. In fact, prior to the Oregon outbreak, there had been only 1 previous instance of resistance. That patient was epidemiologically linked to the Oregon outbreak by a prior hospitalization in the Philippines. In that country, fluoroquinolone-resistant Salmonella are not rare, accounting for 2.5% of isolates in 1993 and 4.7% of isolates in 1998. In the Philippines, fluoroquinolones, as well as many other antimicrobials, are freely available over-the-counter, a situation that undoubtedly contributes to high rates of resistance.
This report also points out that nursing homes are reservoirs of antibiotic-resistant organisms. These organisms can be unusually persistent due to the debilitated state of many residents, a high incidence of antibiotic usage, and the frequent presence of indwelling catheters and pressure sores, locations known to harbor resistant bacteria. The nursing home patients were more likely to carry the resistant Salmonella in the urine than in the stool, a situation that may be fairly unique to nursing homes. Patients transferred to acute care facilities from nursing homes can be the source of resistant organisms in hospitals. In this case, the resistant Salmonella was most likely transmitted to a resident of another nursing home during an overlapping stay in the same hospital.
Finally, this report emphasizes the fact that borders, even oceans, are not an effective barrier to the spread of infectious diseases—and of antibiotic-resistant bacteria in particular. Much of the world is only a few hours by plane from the United States. The consequences of indiscriminate use of antimicrobials and inadequate infection prevention strategies can be visited upon a geographically remote area in a very short time.
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