ARCHIVED - Canadian Integrated Surveillance Report: Salmonella, Campylobacter, verotoxigenic E. coli and Shigella, from 2000 to 2004

Antimicrobial Resistance Trends in Human Salmonella Infections

The ‘Surveillance of Human Clinical Isolates' component of CIPARS, is designed to provide representative data on human Salmonella isolates at the provincial level (See Appendix A – Section 4). A series of studies was initially conducted to support the development of a national antimicrobial resistance surveillance program for enteric pathogens. Between 1997 and 2000, although the differing laboratory methods for bacterial isolation and testing antimicrobial susceptibility may have resulted in biased estimates, there was an indication that resistance could be increasing among certain serovars of Salmonella, particularly for drugs of Very High Importance and High Importance in Human Medicine (Category I and II)⁽¹⁴⁾. In 2003 and 2004, a representative sample of 3056 and 3147 clinical Salmonella isolates were collected from all provincial public health laboratories, respectively. An increase in prevalence of resistance to one or more of 16 antimicrobials tested was observed among S. Heidelberg, S. Typhi, and S. Enteritidis isolates in 2004, compared to the previous year (Table 9). Resistance to ceftiofur increased slightly from 6% of all isolates in 2003 to 7% in 2004^{(17, 18)}. Although resistance to ceftriaxone remained low, its reduced susceptibility in S. Heidelberg isolates (including blood isolates) was of concern, having increased from 8% of isolates in 2003, to 26% in 2004^(15,16).

Selected Phage Types

The number of human isolates of the top four Salmonella serovars that were forwarded to the National Microbiology Laboratory (NML) as part of reference requests, active and passive surveillance, surveys or outbreak and cluster investigations are presented in Table 10. All isolates of these top four serovars, as well as all S. ssp I 4,[5],12:b:-, S. Infantis, S. Newport, S. Oranienburg, S. Panama, S. Thompson and S. Typhi isolates are phage typed, consequently, the total counts in this table indicate the total number of isolates forwarded to the NML. Although Salmonella isolates are sent to the NML as part of CIPARS, submission of non-CIPARS Salmonella isolates can occur and be influenced by enhanced surveillance and outbreak investigations.

The most prevalent phage types among the top four Salmonella serovars from human isolates are shown in Figures 16 to 19. S. Typhimurium PT 104, S. Enteritidis PT 4, and S. Heidelberg PT 19 were the most common phage types identified over the five-year period. Between 2000 and 2004, the proportion of S. Typhimurium PT 104 decreased; S. Enteritidis PT 13 increased; S. Heidelberg PT 19 decreased while PT 29 increased; and S. Hadar PT 47 decreased. The increase in S. Heidelberg PT 29 was observed at the same time as an increase in multi-drug resistance in this strain(16).

Note: All isolates sent to the NML that were phage typed.

Figure 16: Proportion of the top S. Typhimurium phage types from human isolates, 2000 to 2004, NML

Figure 17: Proportion of the top S. Enteritidis phage types from human isolates, 2000 to 2004, NML

Figure 18: Proportion of the top S. Heidelberg phage types from human isolates, 2000 to 2004, NML

Figure 19: Proportion of the top S. Hadar phage types from human isolates, 2000 to 2004, NML