Investigation of an outbreak of gastroenteritis caused by Norwalk-like virus, using solid phase immune electron microscopy

In February 1993, 95 persons (47 patients and 48 staff members) were affect ed by an hospital outbreak of viral gastroenteritis. Using direct electron microscopy (EM) the causative agent was identified as a small round structu red virus. This was confirmed as a Norwalk-like virus using solid phase imm une electron microscopy (SPIEM). Of 94 stool samples examined, 12 (13%) sam ples containing small round structured viruses (SRSV) were SPIEM positive f or Norwalk-like virus. A further 25 (27%) samples contained small round fea tureless virus (SRFV) identified by direct EM and it ere negative on SPIEM. The illness was characterized by preceding influenza-like symptoms in 76% of cases followed by vomiting (76%), diarrhoea (79%) and abdominal pain (79 %). One fatality was recorded. The outbreak lasted for 15 days, with a peak incidence of new cases amongst patients and staff occurring on day 5. It w as controlled through a combination of ward closures, patient cohorting, su spension of duties for affected staff and disinfection procedures. Difficul ties were encountered in the education of staff and in the implementation o f environmental control measures. Screening of hospital catering services a nd a case control study, carried out among affected staff members, failed t o identify a foodborne source. Consumption of tap water in the hospital was commoner among affected staff members than among controls, but this did no t reach significance (P = 0.1). (C) 2000 The Hospital Infection Society.