Epidemiology of rotavirus gastroenteritis.

Infantile gastroenteritis and the resulting dehydrating diarrhoea is a major cause of morbidity in developed countries and of mortality in many developing countries. Since their original description in 1973, rotaviruses have emerged as the single most important cause of diarrhoea in infants and young children requiring admission to hospital for treatment of gastroenteritis.1 A desire to reduce the significant morbidity associated with rotaviruses led to the development of a live attenuated vaccine,2 recently made available for trials in this country. Concurrently, advances in adequate typing systems allowing characterisation of virus from different geographic areas and from sequential infections in populations followed longitudinally have increased our understanding of the epidemiology of this most important group of viruses.3 Knowledge of the epidemiology of rotavirus would be important in the planning of any vaccine programme contemplated for this country. The gastroenteritis associated with rotavirus has consistently been described as more severe than that caused by other agents. The pathophysiology is felt to be loss of absorptive capacity in the small intestine. The incubation period is 48 hours, with viral excretion preceding the onset of symptoms. There is often early vomiting followed by explosive and watery diarrhoea lasting 5-7 days. Virus is usually shed from the 3rd-8th days. Although IgM antibody appears on the 5th day and stays elevated for about three weeks, IgG antibody does not appear until 2-4 weeks after infection.4 Cross-sectional seroepidemiological surveys have shown high antibody levels in the newborn (due to transfer of passive antibody from mother), falling over the first six months of life, peaking again from 2-3 years. High geometric mean titres are then maintained until the age of 40 when levels begin a gradual decline.5 Children aged 6-24 months seem most susceptible to clinical illness following rotavirus infection with peak incidence in most series at 9-12 months. Sequential rotavirus illness can occur in the same child, although such illnesses are characteristically due to different serotypes. A large prospective study in Washington reported 3.7 episodes of rotavirus gastroenteritis per 1000 infants per epidemic year with 2.2 episodes/ 1000/year in the 12-24 month age group. Rotavirus was implicated in 50% of hospitalised episodes of diarrhoea in children under the age of two.6 A prospective study from Copenhagen similarly found rotavirus to be the most frequent pathogen in children hospitalised with gastroenteritis. Incidence was highest under the age of 12 months, with twice as many cases between 6-12 as between 0-6 months.7 Both series noted a decline in incidence of hospitalisation and outpatient visits with age, and a predominance of males among hospitalised patients. Transmission of rotaviruses is assumed to be fecal oral and probably varies with climate, population density and local habits. In temperate climates, rotavirus gastroenteritis peaks in the cooler months, as illustrated by the series from Copenhagen where 85% of isolations occurred from January-April. A similar seasonal trend was noted in Tecumseh.8 In contrast, this virus is seen year round in most tropical climates. *