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Volume 16, Number 11—November 2010

Research

Salmonella enterica Pulsed-Field Gel Electrophoresis Clusters, Minnesota, USA, 2001–2007

Joshua M. RoundsComments to Author , Craig W. Hedberg, Stephanie Meyer, David J. Boxrud, and Kirk E. Smith
Author affiliations: Minnesota Department of Health, St. Paul, Minnesota, USA (J.M. Rounds, S. Meyer, D.J. Boxrud, K.E. Smith); University of Minnesota School of Public Health, Minneapolis, Minnesota, USA (C.W. Hedberg)

Main Article

Table 2

Univariate association between Salmonella enterica serovar frequency, cluster size, cluster density, and cluster being solved, Minnesota, USA, 2001–2007*

Characteristic No. (%) solved clusters No. unsolved clusters Odds ratio (95% confidence interval)
Serovar
Very common† 22 (10) 203 Referent
Common‡ 11 (23) 37 2.74 (1.23–6.13)
Uncommon§ 10 (14) 61 1.51 (0.68–3.37)
Total
43 (13)
301

Cluster size¶
2 16 (8) 194 Referent
3 8 (15) 47 2.06 (0.83–5.11)
4 7 (24) 22 3.86# (1.43–10.40)
>5 12 (24) 38 3.83 (1.68–8.74)
Total
43 (13)
301

Cluster density, d**
0 5 (71) 2 25.8 (3.42–195.37)
1–7 16 (33) 33 5.01 (1.33–18.89)
8–14 11 (22) 40 2.84 (0.73–11.07)
>15 3 (9) 31 Referent
Total 35 (25) 106

*A solved cluster is one that results in identification of a confirmed outbreak.
S. enterica serovars Typhimurium and Enteritidis.
S. enterica serovars Newport, Heidelberg, and Montevideo.
§All other serovars.
¶Significant Mantel-Haenszel χ2 test result for trend (p<0.001).
#Clusters of 4 cases compared with clusters of 3 cases odds ratio 1.87, 95% confidence interval 0.52–6.66.
**Cluster density measured as the number of days from receipt of first cluster case to third case received at the Minnesota Department of Health Public Health Laboratory.

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