Human metapneumovirus prevalence and patterns of genotype persistence identified through surveillance of pediatric pneumonia hospital admissions in coastal Kenya, 2007-2016

Background Human metapneumovirus (HMPV) is an important respiratory pathogen that causes seasonal epidemics of acute respiratory illness and contributes significantly to childhood pneumonia. Current knowledge and understanding on its patterns of spread, prevalence and persistence in communities is limited. Methods We present findings of a molecular-epidemiological analysis of nasal samples from children < 5 years of age admitted with syndromic pneumonia between 2007 and 2016 to Kilifi County Hospital, coastal Kenya. HMPV infection was detected using real-time RT-PCR and positives sequenced in the fusion (F) and attachment (G) genes followed by phylogenetic analysis. The association between disease severity and HMPV genotype was assessed using Chi-square test for independence. Results Over 10 years, 274/6756 (4.10%) samples screened were HMPV positive. Annual prevalence fluctuated between years ranging 1.2% to 8.7% and lowest in the recent years (2014-2016). HMPV detections were most frequent between October of one year to April of the following year. Genotyping was successful for 205/274 (74.8%) positives revealing A2b (41.0%), A2c (10.7%), B1 (23.4%) and B2 (24.9%). The dominance patterns were: genotype A2b between 2007-11, B1 between 2012-14, and A2c in more recent epidemics. Genotype B2 viruses were present in all the years. These patterns mirrored the global picture. Temporal phylogenetic clustering within the genotypes for both local and global sequence data was seen. Genotypes occurring in each epidemic season were comprised of multiple variants. Pneumonia severity did not vary by genotype (p=0.264). In both the F and G gene, the sequenced regions were found to be predominantly under purifying selection. Conclusion Genotype and strain patterns from this rural African setting temporally map with global strain distribution, suggesting a well-mixed global virus transmission pool of HMPV. Persistence in the local community is characterized by repeated introductions of HMPV variants from the global pool. The factors underlying the declining prevalence of HMPV in this population should be investigated.