Epidemiology and costs associated with norovirus outbreaks in NHS Lothian, Scotland 2007–2009

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Summary

Healthcare-associated gastroenteritis outbreaks are becoming more common and are recognized challenges in hospital and community settings. In Edinburgh [NHS (National Health Service) Lothian], all the hospitals and the community were actively monitored for outbreaks of gastroenteritis from September 2007 to June 2009. In total, 1732 patients and 599 healthcare staff were affected in 192 unit outbreaks. In the acute sector, 1368 patients (0.99 cases/1000 inpatient bed-days) and 406 healthcare staff (0.29 cases/1000 inpatient bed-days) were affected in 155 unit outbreaks (0.23 unit outbreaks/day). Noroviruses were detected in 142 outbreaks (74%); 50 were not laboratory confirmed but were presumed to be noroviruses on epidemiological grounds. The closure of affected units to new admissions resulted in the loss of 3678 bed-days. By extrapolation, lost bed-days and staff absence due to gastroenteritis outbreaks cost NHS Lothian £1.2 million for the two norovirus seasons. Outbreaks in which the affected unit was closed within the first three days of recognizing the index case were contained in a mean of six days, and outbreaks in units that were closed later persisted for a mean of seven days; this difference was not statistically significant. Rapid implementation of control measures was effective in the control of outbreaks.

Introduction

Worldwide, healthcare-associated gastroenteritis outbreaks, especially those caused by noroviruses, have been increasing in frequency.1 Outbreaks are generally confirmed rapidly as a result of frequent testing using sensitive real-time reverse transcription–polymerase chain reaction (PCR) assays.2, 3

In England and Wales, the Health Protection Agency Communicable Disease Surveillance Centre operates a surveillance system for gastroenteritis outbreaks, in conjunction with a standardized testing approach.4, 5 A similar system exists in Scotland, where each National Health Service (NHS) board reports ward closures due to gastroenteritis outbreaks on a weekly basis to Health Protection Scotland. Full outbreak details are also submitted regularly as a board brief, and locally as an outbreak report.

Noroviruses are the most common cause of gastroenteritis in the community; as such, it is difficult to avoid introduction of the virus into healthcare settings, particularly in winter months.1, 6, 7, 8 For this reason, control measures are implemented to minimize spread of the virus within and between hospital wards.9, 10, 11 It can be difficult to recognize viral gastroenteritis in hospitalized patients due to the background frequency of incontinence and other causes of gastroenteritis, such as antimicrobial-associated diarrhoea. Within NHS Lothian, patients presenting with an abrupt onset of vomiting and/or watery diarrhoea without underlying causes are alerted to the infection control team or the on-call virologist. With the information presented to the infection control team, clinical management team and capacity co-ordinators, the clinical area may be closed to new admissions and transfers. During the outbreak period, infection control nurses monitor the area regularly to ensure that standard infection control precautions are in place and to provide necessary advice.

Affected wards are advised to send separate stool samples to bacteriology and stool/vomit samples to virology, and to indicate whether samples are from a potential outbreak ward. Early identification of an outbreak promotes the instigation of appropriate infection control measures. After the introduction of real-time RT–PCR in Summer 2007, both vomit and faeces were successfully tested to guide outbreak management. Internal audit data suggest that a higher proportion of vomit samples were positive in comparison with stool samples. If the samples are negative for bacteriology and negative for norovirus, further tests for other organisms such as rotavirus are performed to identify the causative organism.

Patients from affected areas may be discharged home if there is no need for a care package, and relatives are aware of the norovirus situation in the ward and the personal risk to themselves. However, the transfer of affected patients to other hospital clinical areas and nursing homes is avoided unless there is a clinical priority, and following risk assessment. Healthcare workers with gastrointestinal symptoms are taken off duty and advised not to return to work until they have been symptom-free for 48 h. For the duration of the outbreak, staff are allocated to care exclusively for either affected cases or unaffected cases to help prevent spread of the outbreak.

The decision to re-open a ward is made by the infection control team when there have been no new cases for 72 h and there has been no vomiting or diarrhoea for 72 h from the last uncontained episode, or if the symptomatic patients are isolated. A terminal deep clean (remove and change all curtains, remove all bed linen from all beds, decontaminate all care equipment in line with manufacturers’ instructions, and thoroughly clean and then decontaminate all surfaces with a combined detergent/hypochlorite product) is performed before the ward is re-opened.

The standardized overall incidence of gastroenteritis in England between 1993 and 1995 was reported to be 190 cases per 1000 person-years, and a comparable study in The Netherlands in 1991 reported 283 cases per 1000 person-years.12 Although many hospital outbreaks of gastroenteritis have been described, information from systematic, population-based surveillance of gastroenteritis in healthcare settings is lacking.1, 7, 8, 13, 14 In addition, there is a lack of knowledge on the overall cost implications of norovirus outbreaks in healthcare settings, especially in NHS Lothian.

As such, active surveillance of gastroenteritis in NHS Lothian was performed to determine its incidence, microbiological cause, economic cost, and the effectiveness of control measures.

Section snippets

Clinical definitions

Cases of norovirus gastroenteritis typically present with an abrupt onset of vomiting (more than twice in 24 h) and/or three or more episodes of watery diarrhoea in a 24-h period where the patient is not taking antibiotics, regular laxatives or suppositories/enemas. Other symptoms may include fever, abdominal cramps, headache and lethargy. These incidences are alerted to the infection control team or the on-call virologist. An outbreak of gastroenteritis is defined as two or more cases in a ward

Outbreaks, cases and incidences

Within NHS Lothian, 195 outbreaks were investigated in the acute sector and the community (three of the investigated wards were not closed), with 1732 patients and 599 hospital staff meeting the case definition for norovirus infection (Table I). The number of outbreaks in NHS Lothian peaked in November, with 22 episodes in 2007, and began to reduce in May.

Diagnostic results

Specimens were taken for diagnostic analyses in 173 (90%) hospital and community outbreaks. Norovirus was confirmed as the aetiological agent

Discussion

This study investigated the cost of healthcare-associated gastroenteritis outbreaks. On average, each acute hospital had 13 outbreaks, excluding two hospitals which averaged 52 outbreaks over the two-year period. As recommended in national guidelines, 192 of the 195 outbreaks resulted in closure of the ward to new admissions in order to control the spread of disease.11 This closure resulted in the loss of 3678 bed-days, representing approximately 5% of all available acute bed-days over the two

Acknowledgements

The authors wish to thank members of the NHS Lothian Infection Control Team for their assistance with this study, namely R. Broom, C. Calder, W. Evans, I. Forbes, S. Forrest, L. Guthrie, J. Harper, C. Horsburgh, A. Hutcheson, K. Imlach, S. Labonte, C. Mahoney, R. Munro, A. Pringle, C. Rae and J. Richards.

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