Novel microbiological and spatial statistical methods to improve strength of epidemiological evidence in a community-wide waterborne outbreak.

Katri Jalava,Ari Kauppinen,Raisa Loginov,Tarja Pitkänen,Jenni Antikainen,Sallamaari Siponen,Joana Revez,Aino Kyyhkynen,Anja Siitonen,Outi Nyholm,Martti Pärnänen,Leena Maunula,Juhani Merentie,Sirpa Hakkarainen,Markku Kuusi,Jorge W Santo Domingo,Hodon Ryu,Jukka Ollgren,Marja Palander,Pia Räsänen,Ilkka T Miettinen ,Marja‐Liisa Hänninen ,Vicente Gomez‐Alvarez ,Helena Rintala

doi:10.1371/journal.pone.0104713

Abstract

Failures in the drinking water distribution system cause gastrointestinal outbreaks with multiple pathogens. A water distribution pipe breakage caused a community-wide waterborne outbreak in Vuorela, Finland, July 2012. We investigated this outbreak with advanced epidemiological and microbiological methods. A total of 473/2931 inhabitants (16%) responded to a web-based questionnaire. Water and patient samples were subjected to analysis of multiple microbial targets, molecular typing and microbial community analysis. Spatial analysis on the water distribution network was done and we applied a spatial logistic regression model. The course of the illness was mild. Drinking untreated tap water from the defined outbreak area was significantly associated with illness (RR 5.6, 95% CI 1.9–16.4) increasing in a dose response manner. The closer a person lived to the water distribution breakage point, the higher the risk of becoming ill. Sapovirus, enterovirus, single Campylobacter jejuni and EHEC O157:H7 findings as well as virulence genes for EPEC, EAEC and EHEC pathogroups were detected by molecular or culture methods from the faecal samples of the patients. EPEC, EAEC and EHEC virulence genes and faecal indicator bacteria were also detected in water samples. Microbial community sequencing of contaminated tap water revealed abundance of Arcobacter species. The polyphasic approach improved the understanding of the source of the infections, and aided to define the extent and magnitude of this outbreak.

Highlights

Community-wide waterborne outbreaks are characterized by a large number of exposed people with high attack rates [1,2,3,4,5,6]
Such outbreaks may be caused by a failure in the drinking water distribution system [1,3,4] or water treatment breakthrough of contaminating agents due to heavy rainfall or other excess weather conditions [2,5]
When norovirus and sapovirus types are implicated in large scale waterborne outbreaks, this strongly indicates drinking water distribution system contamination by a human faecal sources [10,11]

Summary

Introduction

Community-wide waterborne outbreaks are characterized by a large number of exposed people with high attack rates [1,2,3,4,5,6]. Waterborne outbreaks are frequently associated with large number of symptomatic cases in a point source manner. Such outbreaks may be caused by a failure in the drinking water distribution system [1,3,4] or water treatment breakthrough of contaminating agents due to heavy rainfall or other excess weather conditions [2,5]. When norovirus and sapovirus types are implicated in large scale waterborne outbreaks, this strongly indicates drinking water distribution system contamination by a human faecal sources [10,11]. Sapovirus usually causes sporadic infections [12] but has been isolated from cases of waterborne outbreaks [12,13]

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