Rotavirus Surveillance --- Worldwide, 2009

Rotavirus is the leading cause of severe diarrhea worldwide among children aged <5 years (1). An estimated 527,000 children in this age group died from rotavirus in 2004, and approximately 85% of those deaths occurred in South Asia and sub-Saharan Africa (2). In 2009, the World Health Organization (WHO) recommended inclusion of rotavirus vaccination in all national immunization programs (3). Disease burden data generated from surveillance are important for making decisions regarding whether to introduce rotavirus vaccine into a country, and establishing surveillance platforms is essential to enable monitoring of vaccine impact. WHO coordinates a global surveillance network for rotavirus that uses standardized case definitions and laboratory methods at sentinel hospitals to identify cases of rotavirus in children with diarrhea. This report summarizes an assessment of data from the global surveillance network for 2009, which found that, among 43 participating countries that tested ≥100 stool specimens and reported results for all 12 months in 2009, a median of 36% of enrolled and tested children aged <5 years hospitalized with diarrhea (range: 25%--47% among the six WHO regions) tested positive for rotavirus. These data illustrate the important etiologic role of rotavirus in hospitalizations for diarrhea in children worldwide, which can be prevented by rotavirus vaccination.

Rotavirus surveillance was conducted using standardized case definitions and a common data reporting format (4). Any child aged <5 years who was hospitalized for treatment of acute gastroenteritis or diarrhea at a sentinel hospital conducting surveillance was eligible for enrollment. An enrolled child was defined as one for whom a case report form was completed and a stool specimen was collected, although not necessarily tested. Stool specimens were tested for rotavirus antigen using enzyme immunoassays, generally at the sentinel hospital laboratory or national laboratory. A child whose stool specimen tested positive for rotavirus antigen was defined as having a confirmed case of rotavirus diarrhea.

This report presents data collected through the global surveillance network for rotavirus in 2009. The number of enrolled children and the number of enrolled children with stool specimens tested were stratified by WHO region. The percentage of positive rotavirus results was calculated for all countries, and the median was calculated for all countries and for each WHO region. Countries were included if ≥100 stool specimens were tested in 2009 and the number of tested stool specimens was reported for all 12 months of 2009. A total of 55 countries from the six WHO regions participated in the global network; 43 of these countries met the inclusion criteria.

Among the 43 countries, an average of three (range: 1--13) sentinel hospitals per country conducted surveillance. A total of 45,932 children aged <5 years were enrolled (range: 153--6,227 among countries), and stool specimens from 38,580 children (84%) were tested for rotavirus (range: 111--3,442 among countries) (Table). The median percentage of positive rotavirus results among enrolled children with stool specimens tested in the 43 countries was 36% (range: 12%--68% among countries). By WHO region, the median percentage of positive rotavirus results ranged from 25% in the Region of the Americas to 47% in the Western Pacific Region (Table).

Reported by

Dept of Immunization, Vaccines and Biologicals, World Health Organization (WHO), Geneva, Switzerland. WHO Regional Office for Africa, Brazzaville, Republic of the Congo. WHO Regional Office for the Americas, District of Columbia, United States. WHO Regional Office for the Eastern Mediterranean, Cairo, Egypt. WHO Regional Office for Europe, Copenhagen, Denmark.WHO Regional Office for South-East Asia, New Delhi, India. WHO Regional Office for the Western Pacific, Manila, Philippines. Div of Viral Diseases, National Center for Immunization and Respiratory Diseases, CDC. Corresponding contributor: Mary Agocs, MD, WHO, 41-22-791-1478, agocsm@who.int.

Editorial Note

Among 43 countries participating in the global surveillance network for rotavirus in 2009 that met the inclusion criteria, a median of 36% of diarrhea hospitalizations among children aged <5 years for whom stool specimens were tested were attributable to rotavirus. This detection rate is comparable to the median rotavirus detection rate of 40% among 35 countries with similar regional and global distribution in a report from the rotavirus surveillance networks for 2001--2008 (5). Furthermore, a review of studies examining the period 2000--2004 estimated that 39% of children aged <5 years who were hospitalized with diarrhea had rotavirus infection (1). The high detection rates highlight the etiologic role of rotavirus in severe diarrhea among children worldwide and underscore the need for effective immunization programs to control this disease, as part of a comprehensive approach to prevention and control of diarrhea.

Beginning in 2006, countries worldwide began implementing rotavirus vaccination in their national childhood immunization programs. Countries in the Region of the Americas were among the earliest vaccine adopters. In 2009, the Americas reported the lowest rotavirus detection rate of all regions (25%); eight of the 12 countries in the Americas in this analysis introduced rotavirus vaccine into national immunization programs during 2006--2009, and vaccination coverage levels of >80% among age-eligible children have been achieved in several of these countries. In an earlier report, among 10 countries in the Americas during 2006--2007, a median of 32% of children aged <5 years who were hospitalized with diarrhea tested positive for rotavirus, at a time when eight countries were not using rotavirus vaccine, and after two had introduced rotavirus vaccine in 2006 (6).

Although firm conclusions cannot be drawn from these trend data alone, the decline in rotavirus detection in the Americas following use of rotavirus vaccine might be attributable to vaccination. Indeed, evaluations in some individual countries in the Americas have shown marked declines in rotavirus-specific and diarrhea-related hospitalizations after vaccine introduction (7,8). For example, in El Salvador, which introduced vaccination in 2006, among children aged <5 years, rotavirus-specific hospitalizations declined 69%--81%, and all-cause diarrhea health-care visits during rotavirus season decreased 35%--48% during 2008--2009, compared with prevaccine years (7). Focused analyses of WHO surveillance data from individual countries, with consideration for the year of vaccine introduction, vaccine coverage achieved, age range under surveillance, secular trends in rotavirus diarrhea, and changes in surveillance systems should assist in assessing the impact of rotavirus vaccination on childhood diarrhea hospitalizations.

The findings in this report are subject to at least two limitations. First, sentinel hospitals associated with the global surveillance network for rotavirus are typically health facilities that treat large numbers of children with acute diarrhea, and patients at these sites might not be representative of the total population of children in the country. Second, the variation in rotavirus detection rates among WHO regions might reflect actual differences but might also reflect, in part, differences in ascertainment of rotavirus diarrhea (e.g., enrollment of patients with varying severity of diarrhea and variability in quantity or timing of collection of stool specimens) among countries participating in the network. In 2008, regional surveillance networks for rotavirus were brought under the full coordination of WHO, and efforts are under way to further standardize surveillance procedures, implement performance monitoring indicators, and evaluate laboratory performance in rotavirus antigen detection.

To date, only 27 of 193 WHO member states have introduced rotavirus vaccine into their national immunization programs. Based on data from pivotal trials conducted in the Americas and Europe, WHO recommended routine use of rotavirus vaccines in those regions in 2007 (9). In 2009, WHO expanded the recommendation to include all countries worldwide, after data showing vaccine efficacy in less developed countries in Africa and Asia became available (3). To help overcome financial barriers to wider adoption of rotavirus vaccines, efforts are ongoing to further mobilize resources to fund purchase of rotavirus vaccines for low-income countries. In addition, several emerging-market manufacturers are pursuing development of rotavirus vaccines, which might lead to the availability of additional vaccines at a lower price.

As more countries consider whether to introduce rotavirus vaccine into national immunization programs, documenting the etiologic role of rotavirus in childhood diarrhea hospitalizations through surveillance efforts such as those described in this report will provide important evidence for decision-making. Analysis of surveillance data for trends in the number of rotavirus cases before and after rotavirus vaccine implementation will assist in evaluating vaccination impact, as illustrated by the evidence from early-introducing countries in the Americas (7,8,10).

References

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