Low prevalence of rotavirus and high prevalence of norovirus in hospital and community wastewater after introduction of rotavirus vaccine in Nicaragua

Abstract

Rotavirus (RV) and norovirus (NoV) are major causes of pediatric diarrhea and are altogether associated with approximately 800,000 deaths in young children every year. In Nicaragua, national RV vaccination program using the pentavalent RV5 vaccine from Merck was implemented in October 2006. To determine whether RV vaccination decreased the overall number of RV infections, we investigated the occurrence of RV and NoV in wastewater in the city of León from July 2007 to July 2008 and compared these data with pre-vaccination data. The major finding was the low prevalence of RV compared to NoV in all sampling points (11% vs 44%, p<0.05), and that RV concentration was lower as compared to NoV. RV was observed mainly during the rainy season (July-September), and the majority of all RV detected (6/9) belonged to subgroup (SG) I. The partial VP7-gene obtained from one RV positive sample was similar (99% nt identity) to a G6 VP7-gene of bovine origin and similar to the corresponding gene of the vaccine strain (98%). Furthermore RV G-types 2 and 4 were found in the incoming wastewater. NoV strains were detected throughout the year, of which a majority (20/21) were of genotype GII.4. We conclude that the introduction of RV vaccination reduced the transmission of RV in the community in Nicaragua. However, the burden of diarrhea in the country remains high, and the high prevalence of NoVs in hospital and municipal wastewater is noteworthy. This study highlights the need for further assessment of NoV following RV vaccine introduction.

Figure 1. Concentrations of NoV and RV in different sampling points.

The horizontal lines represent geometric mean with 95% confidence interval.

Figure 2. Phylogenetic analysis of (A) a RV VP7-gene fragment (165 bp, nt 637 to 801, ref acc.no. M12394) isolated from sewage water collected at the local hospital of León, Nicaragua in September 2007.

(B) Partial capsid NS region (282 bp; 5085 to 5366; ref acc.no. X86557) of NoV GII cDNA (n = 21) isolated from sewage water collected at the local hospital and the WWTP of León, Nicaragua in 2007. Both trees were constructed based on the Kimura two-parameter and neighbor-joining methods by use of MEGA 5.0 software. Bootstrap values are shown at the branch nodes (values of <50% are not shown). RV G4Nic181/05 and Sapporo virus GI/1 (ref. acc. no. U65427) were used as outgroups, respectively. For Nicaraguan strains isolated in this study, the number of the sample and clone is given, followed by month of sample collection and site of collection (HO: Hospital; WWTP: Wastewater Treatment Plant).