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Among all the detected clusters (50 clusters with p < 0.05), 11 were consistent with possible WBDO according to the selection criteria above (Table 2 and Figure 6). The impacted grouping of municipalities defined by the algorithm numbered between 500 and 5,000 inhabitants each. Between 20 and 60 cases of AGI were involved in each cluster. The medication rate in the impacted population was approximately 1.4% (median) and varied between 0.7% and 4.8%. The total duration of cumulated WBDO for all the clusters was 177 days, and the longest cluster duration was 35 days. For two of the 11 selected clusters, fecal pollution of DWN during the outbreak (clusters 2 and 10 in Table 2) was detected. For the same two clusters, a notification of WBDO had been made to the local health authority. Moreover, one geographic area (Group ID 207 in Table 2) concerned two clusters, respectively, in 2010 (cluster 6) and in 2012 (cluster 10). The sanitary control of fecal indicators in drinking water highlighted the occurrence of several episodes of non-microbiological compliance between 2009 and 2012 for nine of the 11 clusters detected (mean = 5.6%; min = 0%; max = 14.3%).
Table 2

Description of the 11 clusters of AGI most probably related to contamination of DWN, Auvergne region, 2009–2012

Cluster IDYearArea IDNumber of municipalitiesNumber of DWNPopulation served (inhabitants)Start dateDuration (days)Observed cases of AGIExpected cases of AGIObs/ExpMedication rate in populationaMicrobiological pollution during cluster% of non-microbiological compliancebOther environmental factorsNotification of WBDO to the health authorityp-value
2009 707 4,910 11/26/09 67 13.9 4.8 1.4% No 0.0% YES NO 1.0 × 10−17 
2010 385 1,563 03/19/10 19 33 9.59 3.4 2.1% No 12.2% YES NO 6.0 × 10−4 
2010 155 501 03/31/10 12 24 3.25 7.4 4.8% No 7.1% YES NO 2.4 × 10−8 
2010 638 2,650 06/21/10 42 4.8 8.8 1.6% Yesc 1.5% YES YES 1.0 × 10−17 
2010 207 1,549 08/16/10 35 21 5.29 4.0 1.4% No 8.5% NA NO 4.8 × 10−02 
2010 88 12 5,500 09/09/10 20 72 21.88 3.3 1.3% No 14.3% YES NO 4.0 × 10−12 
2012 31 4,752 02/15/12 34 9.76 3.5 0.7% No 0.0% NA NO 2.3 × 10−4 
10 2012 207 1,549 03/23/12 28 31 9.48 3.3 2.0% Yesd 8.5% YES YES 5.2 × 10−3 
11 2012 452 2,411 03/27/12 15 23 6.16 3.7 1.0% No 5.7% YES NO 3.0 × 10−2 
2012 53 1,933 12/03/12 12 44 8.62 5.1 2.3% No 2.1% NA NO 1.5 × 10−12 
2012 673 3,628 12/03/12 14 48 13.25 3.6 1.3% No 1.2% NA NO 2.3 × 10−8 
Total     30,946  177 439         
Cluster IDYearArea IDNumber of municipalitiesNumber of DWNPopulation served (inhabitants)Start dateDuration (days)Observed cases of AGIExpected cases of AGIObs/ExpMedication rate in populationaMicrobiological pollution during cluster% of non-microbiological compliancebOther environmental factorsNotification of WBDO to the health authorityp-value
2009 707 4,910 11/26/09 67 13.9 4.8 1.4% No 0.0% YES NO 1.0 × 10−17 
2010 385 1,563 03/19/10 19 33 9.59 3.4 2.1% No 12.2% YES NO 6.0 × 10−4 
2010 155 501 03/31/10 12 24 3.25 7.4 4.8% No 7.1% YES NO 2.4 × 10−8 
2010 638 2,650 06/21/10 42 4.8 8.8 1.6% Yesc 1.5% YES YES 1.0 × 10−17 
2010 207 1,549 08/16/10 35 21 5.29 4.0 1.4% No 8.5% NA NO 4.8 × 10−02 
2010 88 12 5,500 09/09/10 20 72 21.88 3.3 1.3% No 14.3% YES NO 4.0 × 10−12 
2012 31 4,752 02/15/12 34 9.76 3.5 0.7% No 0.0% NA NO 2.3 × 10−4 
10 2012 207 1,549 03/23/12 28 31 9.48 3.3 2.0% Yesd 8.5% YES YES 5.2 × 10−3 
11 2012 452 2,411 03/27/12 15 23 6.16 3.7 1.0% No 5.7% YES NO 3.0 × 10−2 
2012 53 1,933 12/03/12 12 44 8.62 5.1 2.3% No 2.1% NA NO 1.5 × 10−12 
2012 673 3,628 12/03/12 14 48 13.25 3.6 1.3% No 1.2% NA NO 2.3 × 10−8 
Total     30,946  177 439         

Clusters presented in the table were selected with the following criteria: cluster duration <7 days, excess cases >10, ratio observed/expected cases of AGI >3, p-value <0.05.

NA, Not available.

aThe medication rate was estimated for the total population of municipalities impacted.

bPercentage of analysis >1 E. coli and/or fecal streptococci for the period 2009–2012.

c900 E. coli UFC/100 mL – 21/06/10.

d >100 E. coli UFC/100 mL – 10/04/12.

Figure 6

Description of the number of cases of AGI according to the day of medical prescription and selected clusters.

Figure 6

Description of the number of cases of AGI according to the day of medical prescription and selected clusters.

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