The norovirus-epidemic in Berlin - clinic, epidemiology, and prevention

INTRODUCTION: During the winter 2002/2003, an increased number of outbreaks of acute gastroenteritis caused by norovirus was reported from Germany, some other European countries and the USA. In this study, the epidemiological and clinical features of the Berlin norovirus outbreak were investigated in order to identify the reasons for the spread of norovirus gastroenteritis and possible control measures. METHODS: Cases and spread of norovirus infection in eleven long-term care facilities and a university hospital in Berlin were monitored from October 2002 to February 2003. To investigate the symptomatology and routes of transmission, a retrospective and interview-based study of infected staff members was performed. RESULTS: Norovirus outbreaks in eleven long-term care facilities affected 314 patients (attack rate: 28.3 %, rate of hospitalisation: 20.7 %). 219 persons were affected in the hospital, during a period of four months. Sequence analysis revealed the circulation of Norovirus genogroup II (Grimsby-like viruses). The mean duration of symptoms was 69 hours. The duration of outbreaks on specific wards was negatively correlated with the time of returning to work (mean: 1.8 days) of the staff members after the disease. DISCUSSION: This report demonstrates the potential of norovirus to cause large outbreaks by person to person transmission. Spread by aerosols generated by vomiting and environmental contamination seem to be particular important in institutional settings. The duration of symptoms was longer than reported previously, reflecting a possible increased virulence. Besides this, the outbreak was facilitated by insufficient preventive measures.