Norovirus outbreak in a district general hospital--new strain identified

Media reports about Norovirus outbreaks, especially in hospitals and nursing homes, have accumulated in the past years. The reasons for this increasing problem are manifold: resistance against common disinfectants, a high level of contagion (a dose of less than 100 particles may be infective); variability of the virus-genome documented by polymerase chain reaction-studies, as well as further factors concerning modern life-style. The following study describes and analyses a Norovirus outbreak in the SRO-Hospital Langenthal from November 25, 2003, to December 31, 2003.

The case definition included sudden vomiting and diarrhoea, abdominal cramps, fever below 38.5 degrees C and recovery after 48 hours. Stool cultures were taken and tested for bacteria (Campylobacter jejuni, salmonella and shigella species) and rotaviruses. Stool and vomit specimens were then tested using Real Time Polymerase Chain Reaction (RT-PCR) for noroviruses using different primer sets. Epidemiological data were gained such as transmission modus from person-to-person or food-borne.

A total of 77 persons were affected by the viral disease. Two incidence-peaks of gastroenteritis were noted. The first peak happened in the geriatric ward and the second in the geographically distinct department of internal medicine. The existence of a new norovirus strain of genogroup II/4 has been confirmed by the CDC Enteric Viruses Branch in Atlanta, GA. The measures to be taken are pointed out.

A norovirus gastroenteritis outbreak of such intensity and extent as described had not thus far occurred in the hospital's history. The strains newly found by sequencing are associated with genogroup II/4. This genogroup caused a striking increase of gastroenteritis outbreaks in Europe in the year 2002 including atypical spring and summer peaks. This new variant is supposed to be more virulent and environmentally more stable than previous strains [21]. Preventive measures that are in agreement with the published guidelines were taken before the viral pathogen was identified by RT-PCR. The obvious emerging problem of norovirus infections in our society and the economic data analysing the costs caused by lost bed days and staff absence make epidemiological investigation of outbreaks and application of molecular tests more important. They are the basis for determining transmission routes and characterising the different strains in order to improve preventive strategies.