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Volume: 24S5 - September 1998 Canadian Integrated Surveillance Report for 1995 on
Salmonella, Non-human Salmonella IsolatesThere were 2,704 non-human isolates of Salmonella reported in
1995 as compared with 4,063 in 1994 and 2,993 in 1993. The increased number
of isolates in 1994 was largely due to increased testing associated with
exported poultry products that year. The distribution of isolates by province
of isolate origin (or the submitting laboratory, if origin not provided)
is displayed in Figure 12 Figure 12
About 65% of the non-human isolates were from Ontario. This partially reflects the size of the poultry and dairy industries in Ontario. Additionally, there are differences in the manner in which isolates are submitted or reported to the national databases across the provinces that likely affect the number of reported cases from each province. Top 10 Serovars The top 10 serovars and number of isolates from non-human sources reported in 1995 to the NLBEP database are listed in Table 6. The top three serovars were the same as in 1994 and 1993, although their rank order changed. The rank order changed among the other top 10 serovars. It should be noted that S. saintpaul was replaced by S. thompson in 1995.
New and Emerging Serovars In 1995, the following six new serovars (defined as serovars showing more than five isolates in 1995 and not reported in 1994) were observed: IIIa:18:z4,z32:- (28 cases), Rough-O:r:1,2 (18 cases), Rough-O:z10:enx (7 cases), S. tilene, S. johannesburg (6 cases), and Rough-O:eh:1,5 (6 cases). Table 7 shows emerging serovars identified2 in 1995. Of these, S. anatum and S. muenster increased in number for 2 years in a row. Both serovars entered the top 10 in 1994 and moved up the top 10 rating in 1995. However, the number of human cases associated with these serovars remained low and fairly stable.
1995 Trends - Non-human Isolates Compared with Human Cases The distributions of non-human Salmonella isolates by time and province are presented in the accompanying Figures (Figures 13-17). As there is no true denominator for these non-human isolates, the human population of each province was used as a proxy denominator. The rates presented have no real meaning but are useful for identifying patterns over time within provinces and general distributions across provinces. All serovars combined showed a moderate seasonal trend, with increased rates in the summer and fall reported from all provinces (Figure 13). Each serovar exhibited a unique relationship between time-space distributions of human and non-human isolates. For example, human cases of S. typhimurium exhibited a uniform distribution both seasonally and geographically, whereas non-human isolates originated predominantly in Ontario and the western provinces and displayed a distinct late summer to early fall seasonal peak (Figures 8 and 14). Although S. enteritidis was the number two serovar associated with human cases and outbreaks in 1994 and 1995, very few isolates from non-human sources were reported in either year. The distribution of S. enteritidis from non-human sources shows some geographic similarity to the distribution of human cases, but the counts are probably too low (n = 44) for a meaningful comparison (Figures 9 and 15). Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
Data from NLBEP and HAL Humanand non-human isolates of S. heidelberg displayed distinctly opposite geographic distributions (Figures 10 and 16). Human cases showed a geographic tendency to occur in Quebec through the Maritimes and a seasonality of summer and fall, but non-human isolates were derived principally from Ontario and the West and exhibited a multi-seasonal distribution with a summertime peak. S. hadar showed very similar geographic and seasonal distributions between human and non-human serovars (Figures 11 and 17). Serovars S. agona and S. infantis demonstrated close geographic similarities but fewer seasonal similarities (Figures not shown). On the other hand, S. thompson, S. newport and S. saintpaul showed closely matching seasonal patterns but only modest geographic likenesses between human and non-human isolates (Figures not shown). Long-Term Trends The trends for the three most frequently isolated serovars from non-human sources in 1995 demonstrate that each serovar had a unique pattern (Figure 18). S. typhimurium isolates declined in frequency from the mid 1980s, whereas S. enteritidis showed a mild increase over the same period (Figures 20 and 21). The annual numbers of S. heidelberg and S. hadar isolates showed considerable variation between 1985 and 1995 and in general increased (Figures 18 and 22). S. newport, S. agona and S. thompson case numbers fluctuated moderately over the 10 years but on the whole showed little change over time. Trends of Human Cases and Non-human Isolates The total number of human cases of salmonellosis decreased from 1985 to 1995, and the number of non-human isolates increased (Figure 19). However, the trends over time for human cases and non-human isolates appear to be more similar for specific serovars such as S. typhimurium (Figure 20), S. enteritidis (Figure 21) and S. heidelberg (Figure 22). The ratio of human to non-human isolates varied from 1.5:1 to 10:1 for these serovars (note change in vertical axes between Figures).
Figure 19
Non-human Isolate Sources The sources for most of the non-human isolates were recorded within the
NLBEP and HAL databases. If the species of origin or source was not one
of the categories listed or was not indicated, the sample was classified
as "Other". Most of the samples were from animals, the environment, feed
products or food. The animal samples included samples from sick animals,
animals in monitoring programs and animals checked as part of outbreak
investigations. The distribution of sources for non-human isolates of
S. typhimurium, S. enteritidis, S. heidelberg and
S. hadar by major food animal species and source of the sample
are shown in Figures 23-26 Figure 23
S. typhimurium and S. enteritidis were distributed across many species and were more prominent in animals than in environmental sources. A large proportion of these isolates were classified as "Other ". On the other hand, S. hadar and S. heidelberg were isolated almost exclusively from poultry (chickens and turkeys) with a large number of isolates from food products. These distributions suggest that investigation of sources for outbreaks and control measures should be directed towards poultry products for these two serovars. Pets as a Reservoir for Salmonella Pets were associated with 115 isolates and 41 serovars of Salmonella (Table 8). There were more isolates from warm blooded pets (66 cases: 54 birds; 4 horses; 1 dog; 7 other) than cold blooded pets (49 cases: 6 turtles; 17 snakes; 9 lizards, newts/skinks; 17 iguanas). The most frequent isolates from cold-blooded pets were S. arizonae (1 iguana, 8 snakes) and S. pomona (4 turtles). The most common isolate from warm-blooded pets was S. typhimurium (54 birds, 3 horses, 1 dog ).
2Emerging serovars were associated with more than 20 isolates in 1995 and had counts such that the difference of the log of the 1995 count and log of the 1994 count exceeded the 75% upper confidence limit of a distribution of the difference for all serovars.
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