B Cryan¹, M Lynch¹, D Whyte¹ on behalf of the Infoscan Southern Communicable Diseases Surveillance Group.
1. Department of Medical Microbiology, Cork University Hospital, Cork, Ireland.

Acute diarrhoeal disease is the commonest single cause of morbidity and mortality worldwide. Infectious diarrhoea has been estimated to cause at least 5 million deaths each year in the developing world (1). Very young children are particularly susceptible to infection and suffer the highest mortality.

Rotavirus is the commonest enteric pathogen in young children in both developing countries and the developed world (1). A striking feature of rotavirus infection in temperate climates is its seasonality. In contrast to other enteric pathogens, which are commonest during the warm months of the year the rotavirus “season” is in winter and spring. Typically children under 2 years of age are affected and rotavirus may be responsible for up to 50% of acute admissions to paediatric units during the winter months (2).

The Republic of Ireland has a population of 3.5 million, 52 722 of whom (1.5%) are under 2 years old (1991 census data). Doctors have a legal responsibility to notify the Department of Health of all cases of gastroenteritis in children under 2 years. In 1995 a total of 3234 notifications were reported. It is reasonable to speculate that rotavirus would be responsible for the vast majority of such infections, but the notifications do not specify the pathogen.

There is no national laboratory based system for collecting data on rotavirus infection. Nevertheless considerable information is available and in this paper we will outline the currently available data from laboratory based surveillance in two regions.

Detection of rotavirus

There are over 50 medical microbiology laboratories in the Republic of Ireland and 16 laboratories examine stool specimens for rotavirus. These laboratories are based in the larger hospitals and/or those with significant paediatric departments. The most popular detection methods are antigen based and only one centre uses electron microscopy.

Rotavirus surveillance in southern and eastern Ireland

In two regions microbiologists, public health doctors, and general practitioners have established clinical and laboratory based recording systems for infectious disease.

These regions cover about 2.5 million people in the south and east of the country.

Laboratory reports of rotavirus and other gastrointestinal infections from the three health board areas in southern Ireland (Munster, population 1.22 million) have been collated each quarter since 1992 (figure 1). Reports of rotavirus infections rose from 361 in 1992 to 536 in 1995. This was not due to increased use of antigen based detection methods as the number of reporting laboratories was constant during the years shown. Rotavirus was the commonest pathogen in 1995 and accounted for 36% of all diarrhoeal agents detected. Campylobacter spp. (19%) and Salmonella spp. (13%) were the second and third commonest pathogens.

Males accounted for 54% of infections. Winter/spring peaks confirmed the expected seasonal pattern. Rotavirus detections tended to be at their lowest in August and September. In 1992 the peak month for rotavirus detection was January, and a second peak occurred in March/April. In 1993 the second peak in April was higher than the one in January (85/61). The peak in 1995 came in June (90). In 1996 this seasonal shift towards spring and summer continued, with 130 reports in March compared with only 28 in January. In the United Kingdom a similar phenomenon was detected in 1995 with a peak in weekly reports in week 20 (May). Data from 1996 confirm this shift of the rotavirus season into late spring (3,4).

Data from the Eastern region of Ireland (Eastern Health Board, population 1.02 million) show that the number of laboratory reports rose in 1995 compared with 1994 (figure 2). The seasonal trends were similar to those seen in the southern region with winter and spring being the periods when the most rotavirus activity was reported and with a similar but less pronounced increase in detections being seen during the second quarter of 1995.

Conclusion

Rotavirus is the commonest enteric pathogen in Irish children. Indeed it is the commonest enteric pathogen overall in the two regions studied. This contrasts with the United Kingdom where Campylobacter spp. and Salmonella spp. are reported more frequently than rotavirus. The reason for this is unclear but the relatively large childhood population in Ireland may account for it at least in part.

Rotavirus vaccines are being developed and some have undergone field trials with promising results. It is likely that such vaccines will become generally available soon. In the Irish context an effective vaccine would have a significant impact on health, both in terms of reducing morbidity and mortality and by conserving health care resources.

To accurately determine the requirement for a rotavirus vaccination programme in Ireland the true epidemiology of rotavirus infection needs to be defined. This aim can be achieved only by setting up a national laboratory based surveillance system. Such a system would also have a major role in assessing the effectiveness of a vaccination programme.

Acknowledgements:

We would like to thank the organisers and contributors of the Munster and Eastern Health Board infectious diseases surveillance schemes who provided the data quoted in this article.

Data from the Munster area are contained in a quarterly newsletter, Infoscan. (http://www.ucc.ie/ucc/faculties/medical/infoscan)

References

1. Syndner JD., Marson M. The global problem of acute diarrhoeal disease: a review of active surveillance data. Bull World Health Organ 1982; 60: 605-13.

2. Herrman JE, Blacklow N. Rotavirus. In Principles and Practice of Infectious Diseases. New York: Churchill Livingston, 1990: 1234-41.

3. Rotavirus infections in humans. Commun Dis Rep CDR Wkly 1996; 6: 85.

4. Rotavirus. Commun Dis Rep CDR Wkly 1996; 6: 163.