Geographically separate outbreaks of shigellosis in Auckland, New Zealand, linked by molecular subtyping to cases returning from Samoa.

Aim: To investigate simultaneous outbreaks of Shigella sonnei gastroenteritis occurring in February 2001 at a health camp for socially deprived children and an elderly care facility.

Methods: Those with symptoms were interviewed using a standardised questionnaire. Cases were defined as having at least three loose stools over a 24 hour period and stool samples requested. A case-control study investigating routes of transmission was performed at the health camp. Environmental investigations of food safety and hygiene were conducted at each facility.

Results: At the camp, 15 (37%) students and 15 (28%) staff met case criteria. Contact with human faeces (OR 4.0; 95% confidence interval 1.0-16.3; p = 0.05) and, for staff, eating camp food (OR 6.9; 1.0-5.0; p = 0.06) were shown to be independent risk factors for illness. At the elderly care facility, four (19%) residents and four (25%) staff met case criteria. Molecular subtyping confirmed that the outbreaks were related to each other and to other cases in travellers returning from Samoa to Auckland and other New Zealand cities over a four month period.

Conclusion: Molecular subtyping is of considerable use in communicable disease investigation, providing strong evidence for links between outbreaks. With expanded technological capability, New Zealand could perform routine molecular subtyping of selected organisms to improve the detection and the investigation of regional and inter-regional outbreaks of infection.