Detection of a previously uncommon salmonella phage in tourists returning from Europe.

Abstract

We suggest that serotyping and phagetyping salmonella strains in returning tourists with gastroenteritis may rapidly detect shifts in salmonella epidemiology in other countries. Tourists returning home may be more prone to seek medical care for acute diarrhoea than citizens of the countries visited. Salmonella enterica serovar Enteritidis is the most common serovar causing food-borne salmonellosis. Since 1980, reported cases of S enteritidis have increased steadily in Europe and North America, caused mainly by strains of phage type (PT) 4 in Europe, and 8 and 13 in the USA and Canada. In epidemiological and environmental studies, eggs and poultry products have been implicated as the main sources.1Mishu B Koehler J Lee LA et al.Outbreaks of Salmonella enteritidis infections in the United States, 1985–1991.J Infect Dis. 1994; 169: 547-552Crossref PubMed Scopus (193) Google Scholar After huge investments in control measures, a decline in the incidence of Salmonella enteritidis has been reported.2Anon.Trends and sources of zoonotic agents in animals, feedstuffs, food and man in the European Union in 1998. European Commission, 2000Google Scholar In Sweden, the yearly incidence of domestic S enteritidis infection is low (1–4 cases per 100 000 population), and of the roughly 2500 cases reported annually from 1997 to 2001, 75–80% were acquired abroad. All Salmonella strains are serotyped, and S enteritidis strains are phagetyped at the Swedish Institute for Infectious Disease Control. Swedish surveillance data show that PT 1 has dominated in travellers returning from Russia, the Baltic countries, and China, and PT 4 from most other European countries. Phage types in returning travellers generally reflect predominant strains in countries visited, as seen in the table.TablePredominant S enteritidis phage types compared with most common phage type found in Swedes returning from these countries 1997–2000*Full list of references available from authors.CountryPredominant phage typeYear of studyMost common phage type in returning touristsDenmark6, 4, 81998–20006, 8Finland1, 419981Germany419984UK41997–20004Italy41990–934Spain4, 6, 141990s1, 4Hungary41992–944Poland8, 41986–954Czech81989–988RepublicSlovakia819958Russia11980–931* Full list of references available from authors. Open table in a new tab In 2001, the most common types were PT 4 and PT 1, accounting for 31% and 17% of all imported cases, respectively, with PT 14b in third place at 13%. This phage type previously accounted for only 1–2% of all S enteritidis cases in Swedes. 62% of the 256 PT 14b cases were reported as acquired in Greece, but also more cases than previously among travellers from Spain and Bulgaria. The increase in tourists returning from Greece was first noted by the Norwegian National Institute of Public Health, and subsequently in Finland. S enteritidis PT 14b is a well known strain, and outbreaks have been related to eggs and egg products (icecream, tiramisu3Moyer NP Salmonella enteritidis surveillance 1995/1996: hygienic laboratory—hotline.http://www.uhl.uiowa.edu/Publications/Google Scholar) or with cross-contamination from poultry.4Kistemann T Dangendorf F Krizek L Sahl HG Engelhart S Exner M GIS-supported investigation of a nosocomial Salmonella outbreak.Int J Hyg Environ Health. 2000; 203: 117-126Crossref PubMed Scopus (25) Google Scholar However, these outbreaks have been local, of limited duration, the source food products have been identified, and the outbreaks contained. The increase in S enteritidis PT 14b may in fact still be an outbreak, except for it is more widespread than previously thought. Alternatively, acquisition or loss of a plasmid or a spontaneous mutation may have resulted in conversion from another phage type to PT 14b. Such change has been described for other phage types, such as a conversion from PT 8 to PT 14b after inoculation into pathogen-free chicken.5Fadl AA Khan MI Genotypic evaluation of Salmonella enteritidis isolates of known phage types by arbitrarily primed polymerase chain reaction.Avian Dis. 1997; 41: 732-737Crossref PubMed Scopus (8) Google Scholar A better adapted, new strain could spread quickly through trade or wild birds. A decrease in phage type 4 reported in Sweden could support such theories. The data from returning Swedish tourists may indicate a shift in predominant S enteritidis phage types in Europe, starting in the southern part of the continent.