Molecular characterization of endemic salmonella infections ... - Evira

2.3 Salmonella in Finland
In Finland all Salmonella strains isolated from humans are sent by laboratories to the National
Public Health Institute in Helsinki, Finland for verification and more accurate epidemiological
classification. This practice has been voluntary from the 1960s onwards and compulsory from
1994. Phagetyping of the serovars Enteritidis, Typhimurium and Paratyphi B is also carried out at
the National Public Health Institute. This intitute has kept a nationwide register on infectious
diseases in humans starting in 1994.
Salmonellosis in humans is relatively rare in Finland: the annual incidence was 44-53 cases per
100 000 inhabitants in 2000-2004, and 85 per cent of these were related to recent foreign travel.
The most common serovars causing infection in humans are the serovars Enteritidis and
Typhimurium. Most cases of S. Enteritidis are of foreign origin whereas the cases of S.
Typhimurium are mainly (90-95%) of domestic origin. In the 1990s, an average of 350 cases per
year of human salmonellosis of domestic origin caused by S. Typhimurium was recorded
compared with an average 160 cases annually in 2000-2004. S. Typhimurium DT1 has been the
predominant phage type except in 1997. S. Infantis is considered endemic in Finland. Of the
isolations made in humans, the majority is usually considered to be of domestic origin. This
especially applies to the isolations found in the 1970s and 1980s. The number of S. Infantis cases
recorded in humans has decreased substantially during the 1990s; an average of 33 cases per
year was recorded in 1995-1999, compared with an average only eight cases annually in 2000-
2004. An increase in S. Agona infections in humans was seen in 1999, with over 80 cases of
infection. In the years 2000-2004, an average of 25 cases annually was recorded (National Public
Health Institute 1965-1994; Ministry of Agriculture and Forestry 2000; Finnish Food Safety
Authority Evira 2006).
Salmonella Agona had been only sporadically isolated from animals in Finland before the small
outbreaks on cattle farms in 1994-1995 and in 1997. S. Agona was not isolated in any farms in
2001-2005 (Figure 1). S. Infantis was rarely [only 4% (20/480) of the Salmonella isolations in 1970]
encountered among animals before the spread among broiler chickens in 1971. The latter caused
an epidemic in both humans and broilers in Finland (Nurmi and Rantala 1972; Rantala 1976). S.
Infantis became more common among cattle throughout Finland in the 1980s, and in the 1990s it
became the predominant Salmonella serovar. In recent years, the number of S. Infantis infected
farms has been five or less (Figure 1). S. Typhimurium has been relatively frequently isolated from
animals ever since its recording was started in 1965. Phage typing of S. Typhimurium isolates
according to the Colindale method began in March 1968. Definitive type (DT) 1 was not
encountered in isolates obtained from animals before 1980. S. Typhimurium DT1 is also
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