A Large Waterborne Gastroenteritis Outbreak in Central Greece, March 2012: Challenges for the Investigation and Management

Epidemiol. Infect. (2014), 142,40–50. © Cambridge University Press 2013 doi:10.1017/S0950268813000939 A large waterborne gastroenteritis outbreak in central Greece, March 2012: challenges for the investigation and management K. MELLOU1*, A. KATSIOULIS2,M.POTAMITI-KOMI1, S. POURNARAS2, M. KYRITSI2,A.KATSIAFLAKA2,A.KALLIMANI1, P. KOKKINOS3, E. PETINAKI4,T.SIDEROGLOU1,T.GEORGAKOPOULOU1, 3 1,2 A. VANTARAKIS AND C. HADJICHRISTODOULOU 1 Hellenic Centre for Disease Control and Prevention, Epidemiological Surveillance and Intervention, Athens, Greece 2 University of Thessaly, Regional Public Health Laboratory of Thessaly, Larissa, Greece 3 University of Patras, Department of Medicine, Public Health, Patras, Greece 4 University of Thessaly, Medical School, Department οf Microbiology, University Hospital of Larissa, Larissa, Greece Received 9 October 2012; Final revision 14 January 2013; Accepted 25 March 2013; first published online 30 April 2013 SUMMARY In March 2012, there was an unusual increase of gastroenteritis cases in a district with 37264 inhabitants in central Greece. It was estimated that more than 3600 people developed symptoms. A 1:1 case-control study showed that consumption of tap water was a risk factor for acquiring infection [odds ratio (OR) 2·18, 95% confidence interval (CI) 1·11–4·28]. Descriptive data, low gastroenteritis incidence in adjacent areas with different water supply systems, and water-quality data further supported the hypothesis of a waterborne outbreak. Thirty-eight stool samples were positive for rotavirus. Bacterial indicators of recent faecal contamination were detected in samples from the water source and ice cubes from a local production enterprise. Molecular epidemiology of rotavirus strains, apart from the common strain, G3[P8], identified the unusual G/P combination G2P[8]. Water sanitation measures contributed to the control of the outbreak. This outbreak demonstrated the need for the cooperation of laboratories with different expertise and the importance of early notification of waterborne gastroenteritis outbreaks. Key words: Gastroenteritis, outbreaks, rotavirus, virus infection, waterborne infections. INTRODUCTION Several factors, such as the improvement of recording Waterborne gastroenteritis outbreaks (WBOs) caused and the enhancement of laboratory methods have contributed to the recent increased detection of by the consumption of contaminated drinking water – are usually extensive since a large number of people WBOs [4 5]. According to the data of the European are served by the same water supply system [1–3]. Centre for Disease Control and Prevention, the actual incidence of WBOs is probably underestimated [6]. In Greece, notification of WBOs is included in the mandatory notification system. Thirteen WBOs were * Author for correspondence: Dr K. Mellou, Hellenic Centre for reported from 2004 to 2011 with a mean number of Disease Control and Prevention, Epidemiological Surveillance and – Intervention, 3-5 Agrafon Str, Athens 15123, Greece. cases of 174 (S.D.=231·4) [7 9]. Several bacteria, para- (Email: [email protected]) sites and viruses have been identified as aetiological Downloaded from https://www.cambridge.org/core. IP address: 170.106.33.14, on 28 Sep 2021 at 21:10:34, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268813000939 Large waterborne outbreak in Greece 41 Fig. 1 [colour online]. Map of Elassona district highlighting the area of Elassona city and the surrounding villages with the same water supply system, Greece, March 2012. agents of WBOs worldwide, but very frequently the The HCDCP decided to further investigate the out- reported WBOs are of mixed aetiology [10–14]. break in collaboration with the local public health On 14 March 2012, the Hellenic Center for Disease authorities. The objectives of the investigation were Control and Prevention (HCDCP) was informed by the identification of the mode and vehicle of trans- the Health Care Centre (HCC) of Elassona about mission, as well as of possible risk factors, in order an unusual increase of gastroenteritis cases since to implement appropriate control measures. 10 March. Most cases were residents of Elassona, a district in central Greece with 37264 inhabitants. METHODS The city of Elassona (7233 inhabitants) and 5/52 villages of the district (1337 inhabitants) are served Descriptive epidemiology and estimation of the extent by the same water supply system, while the rest of of the outbreak the villages utilize autonomous systems (Fig. 1). The An active case-finding was initiated and medical altitude of Elassona is 311 m and its geography doctors of Elassona HCC were requested to provide includes farmlands in the valley areas, mountains to the total number of gastroenteritis cases from the west and east and forests in the west and east as Elassona district they had treated since the 1 March fl well as grasslands. A river ows through Elassona and their demographic characteristics. Ιnformation and divides the town into two parts, which are con- on the place of residence and the date of symptom nected by four bridges. onset was also collected. To assess the extent of the The main hypothesis formulated was that this was a outbreak more than 200 houses, distributed through- WBO as there was heavy rainfall in the region the out the region, were visited. The total number of week before the onset of the gastroenteritis cases people living in each house and the number of persons and several patients had reported that the water that had developed gastroenteritis were recorded and during the same period was coloured. In addition, the attack rate was estimated. cases were distributed in both parts of the town and Finally, information on absence from schools similar outbreaks had occurred in the past during (elementary and high schools) of Elassona and spring after heavy rains. Tsaritsani, an adjacent city with 2507 residents that Downloaded from https://www.cambridge.org/core. IP address: 170.106.33.14, on 28 Sep 2021 at 21:10:34, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268813000939 42 K. Mellou and others has a different water supply system, was collected. It testing for rotavirus, adenovirus and norovirus was should be noted that by the time the outbreak was performed. notified, pre-schools/nurseries had already been closed because of the increased number of ill children. This is actually indicative of the high attack rate in toddlers. Analytical epidemiology A case-control study with 1:2 ratio was designed. Since most of the cases were residents of Elassona, Environmental investigation and water sampling it was decided that the study population should be The spring water source of the supply system of restricted to the residents of the city. Elassona is situated in a valley, 7 km north of the A probable gastroenteritis case was defined as city, crossed by a river. The water of the river is in any resident of Elassona that presented: (a) acute contact with the walls of the cement reservoir tank diarrhoea (three or more episodes) or (b) vomiting in which water from the source is gathered. In the and one or more episodes of loose stools in a 24-h basin of the river, several animal breeding farms period between 6 and 17 March and a confirmed (goats, sheep, cows, pigs) and houses are located. case as a probable case that was laboratory confirmed. The spring water is transferred from the reservoir One hundred and fifty-one cases were randomly tank to a tank in the city, where chlorination takes selected from the total recorded cases of the place before distribution. Self-assessment micro- HCC for which the place of residence was known. biological tests are conducted by the municipality Controls were selected from the residents of the city water authority on a monthly basis according to who had not developed gastroenteritis symptoms national legislation of water intended for human con- during the same period and were matched to cases sumption (KYA Y2/38295/2007 ΦEK 630/26-4-2007). by age group (<15, 15–30, 31–45, 46–60, >60 years) Almost half of the houses in Elassona are served and gender (frequency matching). Controls were by the public sewage system. Cases originated from selected from the houses closest to the cases’ houses. houses with public or private systems. Each family provided no more than one case and The public water supply system was inspected on 16 one control. of March by the Regional Public Health Laboratory A standardized questionnaire was used to obtain (RPHL) of Thessaly. information on demographic characteristics, clinical On 16 March, health inspectors of RPHL of manifestations and severity of the disease, prior con- Thessaly collected six water samples – three for micro- tact with ill persons, participation in social activities/ biological analysis and three for chemical analysis – events, food consumption, water consumption and from the source, the tank and tap water and placed the number of glasses of water consumed daily. The a filter at the source (Gelman, Germany), for Cryptos- questionnaire also included questions on a number poridium detection. Water samples were also collected of proxies for exposure to tap water: consumption of on 6 April (n=4) and 11 April (n=4) after heavy rain- bottled water, use of tap water for washing fruit and fall, both from the tank and the source for microbio- vegetables, for cleaning teeth, for making ice cubes, logical and chemical analysis. and diluting juices, use of water filters, and use of a All water samples were obtained under sterile con- dish washer. All questions concerned the 10 days ditions, placed in sterile containers and transported prior to the disease onset. Since the aetiological to the laboratory in a cool box (5±3 °C) within a agent was unknown, the chosen time period was few hours. The microbiological and chemical examin- wide enough to cover a large spectrum of pathogens.

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