Large waterborne Campylobacter outbreak: use of multiple approaches to investigate contamination of the drinking water supply system, Norway, June 2019

Abstract

On 6 June 2019, the Norwegian Institute of Public Health was notified of more than 50 cases of gastroenteritis in Askøy. A reservoir in a water supply system was suspected as the source of the outbreak because of the acute onset and geographical distribution of cases. We investigated the outbreak to confirm the source, extent of the outbreak and effect of control measures. A case was defined as a person in a household served by Water Supply System A (WSS-A) who had gastroenteritis for more than 24 h between 1 and 19 June 2019. We conducted pilot interviews, a telephone survey and an SMS-based cohort study of residents served by WSS-A. System information of WSS-A was collected. Whole genome sequencing on human and environmental isolates was performed. Among 6,108 individuals, 1,573 fulfilled the case definition. Residents served by the reservoir had a 4.6× higher risk of illness than others. Campylobacter jejuni isolated from cases (n = 24) and water samples (n = 4) had identical core genome MLST profiles. Contamination through cracks in the reservoir most probably occurred during heavy rainfall. Water supply systems are susceptible to contamination, particularly to certain weather conditions. This highlights the importance of water safety planning and risk-based surveillance to mitigate risks.

Keywords: Campylobacter; Norway; climate; disease outbreaks; drinking; extreme weather; gastroenteritis; water supply.

Figure 1

Water supply zones of water supply system WSS-A defined by different reservoirs, Askøy, Norway, 2019

Figure 2

Number of gastroenteritis consultations (including telephone consultations) at OPHS and GP offices, Askøy, Norway, 3–14 June 2019 (n = 1,056) and timeline of action points

Figure 3

Estimated incidence rates for gastroenteritis consultations linked to reservoir supply zones, Askøy, Norway, 6 June 2019

Figure 4

Distribution of cases by date of symptom onset, Askøy, Norway, 1–19 June 2019 (n = 1,573)

Figure 5

Data on rainfall from a nearby weather station and onset of consultations for gastroenteritis registered in the Norwegian Syndromic Surveillance System (NorSySS), Askøy, 1 April–20 June 2019 (n = 948)