Linking healthcare associated norovirus outbreaks: a molecular epidemiologic method for investigating transmission.

BACKGROUND: Noroviruses are highly infectious pathogens that cause gastroenteritis in the community and in semi-closed institutions such as hospitals. During outbreaks, multiple units within a hospital are often affected, and a major question for control programs is: are the affected units part of the same outbreak or are they unrelated transmission events? In practice, investigators often assume a transmission link based on epidemiological observations, rather than a systematic approach to tracing transmission.Here, we present a combined molecular and statistical method for assessing:1) whether observed clusters provide evidence of local transmission and2) the probability that anecdotally|linked outbreaks truly shared a transmission event. METHODS: 76 healthcare associated outbreaks were observed in an active and prospective surveillance scheme of 15 hospitals in the county of Avon, England from April 2002 to March 2003. Viral RNA from 64 out of 76 specimens from distinct outbreaks was amplified by reverse transcription-PCR and was sequenced in the polymerase (ORF 1) and capsid (ORF 2) regions. The genetic diversity, at the nucleotide level, was analysed in relation to the epidemiological patterns. RESULTS: Two out of four genetic and epidemiological clusters of outbreaks were unlikely to have occurred by chance alone, thus suggesting local transmission. There was anecdotal epidemiological evidence of a transmission link among 5 outbreaks pairs. By combining this epidemiological observation with viral sequence data, the evidence of a link remained convincing in 3 of these pairs. These results are sensitive to prior beliefs of the strength of epidemiological evidence especially when the outbreak strains are common in the background population. CONCLUSION: The evidence suggests that transmission between hospitals units does occur. Using the proposed criteria, certain hypothesized transmission links between outbreaks were supported while others were refuted. The combined molecular/epidemiologic approach presented here could be applied to other viral populations and potentially to other pathogens for a more thorough view of transmission

Epidemiology and Cost of Nosocomial Gastroenteritis, Avon, England, 2002–2003

Implementing control measures rapidly may be effective in controlling gastroenteritis outbreaks

Prevention of post splenectomy sepsis: a population based approach.

Background The aim of the study was to prevent the occurrence of serious, overwhelming infection following splenectomy, by a district based initiative. Subjects were residents of Plymouth and Torbay District Health Authority (DHA) who had undergone splenectomy in the past and general practitioners (GPs) within the District. Methods District guidelines on the prevention of post splenectomy sepsis were developed and disseminated among local GPs and hospital doctors. Patients who had undergone operative splenectomy were actively traced through GP and hospital information systems so that they could be offered sepsis preventive measures in accordance with the guidelines. Data capture-recapture was used as an ascertainment adjustment method to estimate the district prevalence of alive patients who have had an operative splenectomy. A postal questionnaire of district GPs was undertaken after one year to determine their awareness and use of the guidelines. Results Eight-eight alive patients who had undergone splenectomy were not previously identified by their GP as being asplenic.They were traced so that they could be offered sepsis preventive measures in line with the local guidelines. The estimated district prevalence of individuals who had had an operative splenectomy after ascertainment adjustment using data capture-recapture is ρ′ =9.75 per 10000 population [95 per cent confidence interval (Cl) (7.87, 11.64) per 10000]. Out of 367 district GPs, 201 used the local guidelines after one year Conclusions Effective prevention of overwhelming infection following splenectomy requires an active population based approach