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Improving resolution of public health surveillance for human Salmonella enterica serovar Typhimurium infection: 3 years of prospective multiple-locus variable-number tandem-repeat analysis (MLVA).

Sintchenko V, Wang Q, Howard P, Ha CW, Kardamanidis K, Musto J, Gilbert GL - BMC Infect. Dis. (2012)

Bottom Line: The diversity of the STM population remained relatively constant over time.The gradual increase in the number of STM cases during the study was not related to significant changes in the number of clusters or their size. 667 different MLVA types or patterns were observed.Prospective MLVA typing of STM allows the detection of community outbreaks and demonstrates the sustained level of STM diversity that accompanies the increasing incidence of human STM infections.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Infectious Diseases and Microbiology-Public Health, Institute of Clinical Pathology and Medical Research, Westmead Hospital, Sydney, NSW 2145, Australia. vitali.sintchenko@swahs.health.nsw.gov.au

ABSTRACT

Background: Prospective typing of Salmonella enterica serovar Typhimurium (STM) by multiple-locus variable-number tandem-repeat analysis (MLVA) can assist in identifying clusters of STM cases that might otherwise have gone unrecognised, as well as sources of sporadic and outbreak cases. This paper describes the dynamics of human STM infection in a prospective study of STM MLVA typing for public health surveillance.

Methods: During a three-year period between August 2007 and September 2010 all confirmed STM isolates were fingerprinted using MLVA as part of the New South Wales (NSW) state public health surveillance program.

Results: A total of 4,920 STM isolates were typed and a subset of 4,377 human isolates was included in the analysis. The STM spectrum was dominated by a small number of phage types, including DT170 (44.6% of all isolates), DT135 (13.9%), DT9 (10.8%), DT44 (4.5%) and DT126 (4.5%). There was a difference in the discriminatory power of MLVA types within endemic phage types: Simpson's index of diversity ranged from 0.109 and 0.113 for DTs 9 and 135 to 0.172 and 0.269 for DTs 170 and 44, respectively. 66 distinct STM clusters were observed ranging in size from 5 to 180 cases and in duration from 4 weeks to 25 weeks. 43 clusters had novel MLVA types and 23 represented recurrences of previously recorded MLVA types. The diversity of the STM population remained relatively constant over time. The gradual increase in the number of STM cases during the study was not related to significant changes in the number of clusters or their size. 667 different MLVA types or patterns were observed.

Conclusions: Prospective MLVA typing of STM allows the detection of community outbreaks and demonstrates the sustained level of STM diversity that accompanies the increasing incidence of human STM infections. The monitoring of novel and persistent MLVA types offers a new benchmark for STM surveillance.A part of this study was presented at the MEEGID × (Molecular Epidemiology and Evolutionary Genetics of Infectious Diseases) Conference, 3-5 November 2010, Amsterdam, The Netherlands.

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Sensitivity of cluster definition.
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Figure 4: Sensitivity of cluster definition.

Mentions: The sensitivity of a STM MLVA typing based cluster definition was tested to identify the association between the number of cases (x) with matching STM MLVA types per 4-week period and the number of clusters (y) potentially reported. Four cluster definitions (Figure 4) were contrasted, including (i) three or more cases; (ii) five or more cases; (iii) seven or more cases, and (iv) ten or more cases of matching MLVA type obtained in a 4-week time period. The regression model expressed the relationship: y = 3.025 × 2 - 53.63 × + 275.8. Sensitivity analysis of MLVA typing-based clustering identified 33-91 MLVA clusters based on different definitions, involving 77-83% of all STM isolates tested. The decrease of the number of cases to three or more would significantly increase the number of clusters reported. The average number of isolates per cluster varied between 8.6 (range 2-81) and 19.3 (range 5-166). The change in the minimum duration of a cluster from 2 to 8 weeks did not significantly affect the final number of MLVA clusters detected.


Improving resolution of public health surveillance for human Salmonella enterica serovar Typhimurium infection: 3 years of prospective multiple-locus variable-number tandem-repeat analysis (MLVA).

Sintchenko V, Wang Q, Howard P, Ha CW, Kardamanidis K, Musto J, Gilbert GL - BMC Infect. Dis. (2012)

Sensitivity of cluster definition.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3368731&req=5

Figure 4: Sensitivity of cluster definition.
Mentions: The sensitivity of a STM MLVA typing based cluster definition was tested to identify the association between the number of cases (x) with matching STM MLVA types per 4-week period and the number of clusters (y) potentially reported. Four cluster definitions (Figure 4) were contrasted, including (i) three or more cases; (ii) five or more cases; (iii) seven or more cases, and (iv) ten or more cases of matching MLVA type obtained in a 4-week time period. The regression model expressed the relationship: y = 3.025 × 2 - 53.63 × + 275.8. Sensitivity analysis of MLVA typing-based clustering identified 33-91 MLVA clusters based on different definitions, involving 77-83% of all STM isolates tested. The decrease of the number of cases to three or more would significantly increase the number of clusters reported. The average number of isolates per cluster varied between 8.6 (range 2-81) and 19.3 (range 5-166). The change in the minimum duration of a cluster from 2 to 8 weeks did not significantly affect the final number of MLVA clusters detected.

Bottom Line: The diversity of the STM population remained relatively constant over time.The gradual increase in the number of STM cases during the study was not related to significant changes in the number of clusters or their size. 667 different MLVA types or patterns were observed.Prospective MLVA typing of STM allows the detection of community outbreaks and demonstrates the sustained level of STM diversity that accompanies the increasing incidence of human STM infections.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Infectious Diseases and Microbiology-Public Health, Institute of Clinical Pathology and Medical Research, Westmead Hospital, Sydney, NSW 2145, Australia. vitali.sintchenko@swahs.health.nsw.gov.au

ABSTRACT

Background: Prospective typing of Salmonella enterica serovar Typhimurium (STM) by multiple-locus variable-number tandem-repeat analysis (MLVA) can assist in identifying clusters of STM cases that might otherwise have gone unrecognised, as well as sources of sporadic and outbreak cases. This paper describes the dynamics of human STM infection in a prospective study of STM MLVA typing for public health surveillance.

Methods: During a three-year period between August 2007 and September 2010 all confirmed STM isolates were fingerprinted using MLVA as part of the New South Wales (NSW) state public health surveillance program.

Results: A total of 4,920 STM isolates were typed and a subset of 4,377 human isolates was included in the analysis. The STM spectrum was dominated by a small number of phage types, including DT170 (44.6% of all isolates), DT135 (13.9%), DT9 (10.8%), DT44 (4.5%) and DT126 (4.5%). There was a difference in the discriminatory power of MLVA types within endemic phage types: Simpson's index of diversity ranged from 0.109 and 0.113 for DTs 9 and 135 to 0.172 and 0.269 for DTs 170 and 44, respectively. 66 distinct STM clusters were observed ranging in size from 5 to 180 cases and in duration from 4 weeks to 25 weeks. 43 clusters had novel MLVA types and 23 represented recurrences of previously recorded MLVA types. The diversity of the STM population remained relatively constant over time. The gradual increase in the number of STM cases during the study was not related to significant changes in the number of clusters or their size. 667 different MLVA types or patterns were observed.

Conclusions: Prospective MLVA typing of STM allows the detection of community outbreaks and demonstrates the sustained level of STM diversity that accompanies the increasing incidence of human STM infections. The monitoring of novel and persistent MLVA types offers a new benchmark for STM surveillance.A part of this study was presented at the MEEGID × (Molecular Epidemiology and Evolutionary Genetics of Infectious Diseases) Conference, 3-5 November 2010, Amsterdam, The Netherlands.

Show MeSH
Related in: MedlinePlus