616 Norovirus outbreaks in UK NHS Hospitals: not a problem in the US?

Saturday, March 20, 2010
Grand Hall (Hyatt Regency Atlanta)
Ben Lopman, PhD , Health Protection Agency, London, United Kingdom
John P. Harris, MSc , Health Protection Agency, London, United Kingdom
G. K. Adak, PhD , Health Protection Agency, London, United Kingdom
Background: Noroviruses are a well-recognized cause of outbreaks of gastroenteritis in UK National Health Service hospitals.  Objective: We present results from a collection of studies aiming to quantify the burden of norovirus in these settings.
Methods: (a) Active prospective follow-up of 15 hospitals from three hospital systems for one year.  Standard definitions of cases and outbreaks with PCR diagnostics for norovirus (b) Analysis of national hospital admissions and mortality datasets. ICD-10 codes relating to infectious and non-infections gastroenteritis were modeled against a time-series of norovirus incidence based on laboratory surveillance. Goodness-of-fit was calculated; annual number of hospital admissions and deaths were estimated.
Results: (a) In the 171 inpatient units followed, a total of 227 outbreaks occurred; the outbreak incidence was 1.33 (05% CI 1.16–1.51) outbreaks per unit-year of risk.  63% were confirmed due to norovirus.  As a control measure, admissions were restricted onto 70% affected units, resulting in an economic loss of $1.0 million per 1000 beds/year. The incidence among patients was 2.21 cases per 1,000 hospital-days at risk and among staff was 0.47 cases per 1,000 hospital-days at risk. (b) Norovirus disease was estimated to cause 1.17 and 0.55 per 1000 emergency admissions in elderly and adults patients (R2 = 0.89 and 0.85, respectively), corresponding to approximately 3000 hospitalizations annually.  20% (13.3%–26.8%) of deaths in persons >65 years of age caused by infectious gastroenteritis other than Clostridium difficile were associated with norovirus infection in this period and 13% (7.5%–18.5%) of deaths caused by noninfectious gastroenteritis were associated with norovirus. An estimated 80 deaths each year in this age group may be associated with norovirus infection.

Conclusions: Norovirus outbreaks are frequent and have substantial cost implications in UK NHS hospitals.  Outbreaks pose a substantial risk of morbidity and associated-mortality to patients and are an occupational risk to staff.  Such outbreaks are rarely reported from US hospitals.  This presentation will conclude by exploring the possible reasons for such apparent differences between the epidemiology in US and UK hospitals.