African Rotavirus Surveillance Network – A Brief Overview

Abstract

With the imminent availability of new and prospective rotavirus vaccines, reliable information on burden of rotavirus diseases in the different African countries was required to enable evidence-based decision-making regarding introduction of rotavirus vaccines. WHO has been supporting member states since 2006 to establish sentinel surveillance for rotavirus diarrhea in children <5 years of age using standardized guidelines. African countries are using this platform to generate high quality country specific data to document and demonstrate the burden of rotavirus gastroenteritis. The data gathered are being used by policy makers to guide decisions on appropriate intervention strategies for diarrhea control including the value and timing of the introduction of new rotavirus vaccines in the national immunization programs.

The World Health Organization Regional Office for Africa (WHO AFRO) has been supporting Ministries of Health to establish, strengthen and expand surveillance for diseases targeted by new vaccines as part of implementation of the Global Framework for Immunization, Monitoring, and Surveillance and regional Integrated Disease Surveillance and Response (1, 2). As part of this initiative, the African Rotavirus Surveillance Network was established in 2006 to generate country- and region-specific data on the burden of rotavirus diarrhea and to characterize and document the circulating rotavirus strains. These data were anticipated to inform decisions on rotavirus vaccine introduction into national immunization programs. Where possible, rotavirus surveillance was integrated with the surveillance for other vaccine preventable diseases including pediatric bacterial meningitis surveillance network that is similarly coordinated by WHO AFRO (3). Hospital sites were selected based on defined criteria including those that cumulatively care for at least 100 children less than five years of age hospitalized for acute gastroenteritis per year. Also, hospital sites should have laboratory capabilities required to perform rotavirus diagnosis. WHO supports and contracts designated Regional Rotavirus Reference Laboratories (RRL) and local universities to conduct regular training of participants from the network countries on rotavirus diagnostic techniques and good laboratory procedures as well as support regional external quality assurance (EQA) and quality control (QC) programs. These RRLs also conduct rotavirus strain characterization to determine circulating rotavirus strains in the African region.

Over the past 7 years, the African Rotavirus Surveillance Network (ARSN) coordinated by WHO AFRO has expanded from 4 sentinel sites located in 4 countries in 2006 to 34 sentinel sites located in 20 countries in 2012 (Figure 1). Each of the participating sentinel hospitals conducts active surveillance for rotavirus diarrhea using a common surveillance protocol including case definition, laboratory techniques and data capture, sharing and analysis (4,5). Briefly, children who present to a sentinel hospital and meet the case definition (≥3 episodes of diarrhea (stools of a less formed character than usual) within a 24 hour period, less than 7 days prior to hospital visit, which is not explained by an underlying medical condition) are enrolled and a stool specimen collected. Basic demographic and clinical information is collected for every enrolled child. Stool specimens are tested by enzyme immunoassay at the sentinel hospital laboratories. A proportion of positive specimens are selected at random to represent all the months of the year and sent to RRLs for genotyping using RT-PCR.

Figure 1: African countries conducting rotavirus surveillance.

Note: Morocco, Tunisia, Libya, Egypt, Sudan, South Sudan, Djibouti, and Somalia are not part of the African Surveillance Network. They report data to Eastern Mediterranean Surveillance Network coordinated by WHO.

From 2006 to 2012, a total of 42,693 children <5 years of age hospitalized for acute diarrhea in sentinel hospitals participating in the ARSN network and reporting to WHO have been enrolled in the surveillance program (Table 1). Stool specimens were collected and tested from 38,950 (91%) of these children. The number of children enrolled annually has increased as the network has expanded over the last 7 years. A total of 15,313 (40.7%) specimens tested positive for rotavirus during the entire period with the percent positive ranging from 35.6% in 2008 to 49.1% in 2006.

Table 1:

Proportion of diarrheal hospitalizations among children < 5 years positive for rotavirus in Sub-Saharan countries, 2006-2012

Year	No. of countries reporting	No of hospital sites	No. acute diarrhoea hospitalizations	No. with stool specimen collected (%)	No. stool specimen tested	No. (%) specimens confirmed rotavirus by ELISA
2006	4	4	1351	1206 (89.3)	1202	590 (49.1)
2007	7	7	2046	1847 (90.3)	1847	799 (43.3)
2008	8	11	3533	3344 (94.7)	3225	1149 (35.6)
2009	11	16	4944	4763 (96.3)	4643	1811 (39.0)
2010	16	29	10972	9484 (86.4)	9241	3987 (43.1)
2011	18	32	10222	9289 (90.9)	8759	3538 (40.4)
2012	20	34	9625	9017 (93.7)	8668	3439 (39.6)
Total			42693	38950 (91.2)	37585	15313 (40.7)

Great variability in circulating strains has been observed from year to year. G1P[8] was consistently the most prevalent strain varying from 14% −31% of all circulating strains, mixed G and P strains were also commonly detected during the period 2009-2012 Figure 2). Strains such as G2P[4], G3P[8], and G4P[8], which are routinely detected in developed countries are less common in Africa. Conversely, there are a number of strains commonly detected in the African region, accounting for 28%-38% of circulating strains annually that are less common in developed countries In this regard, it is reassuring that clinical trials of rotavirus vaccines in Africa found that the vaccine effectiveness was similar against vaccine and non-vaccine strains (6). However, it is important to continue monitoring the rotavirus strains circulating in various settings as tremendous diversity of strains exists and not all could be evaluated in the clinical trials.

Figure 2. Rotavirus genotype distribution in African countries, 2009–2012.

The African Rotavirus Surveillance Network has played an important role in establishing the burden of rotavirus disease in Africa and the data has facilitated country decisions on rotavirus vaccine implementation. With the increased awareness of the local epidemiology of rotavirus diarrhea and the availability of rotavirus disease burden data contributed by the surveillance network, countries have begun to introduce rotavirus vaccines into their national immunization programs with financial support from GAVI. The rotavirus surveillance network is also adapting to meet local needs for monitoring the impact of the vaccine program (7, 8). For example, Ghana and South Africa, the first countries in Africa to introduce rotavirus vaccines into their national immunization program are using rotavirus surveillance to monitor trends in rotavirus diarrhea pre- and post-vaccine introduction as well as using their surveillance sites as a platform to evaluate rotavirus vaccine effectiveness (9). Similarly, Rwanda, which joined the network in 2010 and introduced rotavirus vaccine in May 2012, and Tanzania, which introduced vaccine in 2013, are also conducting a vaccine impact evaluation through their surveillance platforms.

As more countries in Africa introduce rotavirus vaccine, the network will continue to play an important role in the monitoring of impact of vaccine and providing key data to policymakers, physicians and parents to encourage and sustain the use of vaccine national immunization programs. This model of using a surveillance program to generate data to facilitate and sustain introduction of a new vaccine can be adapted as other new vaccines become available for use. Also, this network can serve as a platform at the country level to collect data on additional disease causing pathogens.