Global seasonality of rotavirus disease

Abstract

Background: A substantial number of surveillance studies have documented rotavirus prevalence among children admitted for dehydrating diarrhea. We sought to establish global seasonal patterns of rotavirus disease before the introduction of widespread vaccination.

Methods: We reviewed studies of rotavirus detection in children with diarrhea published since 1995. We assessed potential relationships between seasonal prevalence and locality by plotting the average monthly proportion of diarrhea cases positive for rotavirus according to geography, country development and latitude. We used linear regression to identify variables that were potentially associated with the seasonal intensity of rotavirus.

Results: Among a total of 99 studies representing all 6 geographic regions of the world, patterns of year-round disease were more evident in low- and low-middle income countries compared with upper-middle and high-income countries where disease was more likely to be seasonal. The level of country development was a stronger predictor of strength of seasonality (P = 0.001) than geographic location or climate. However, the observation of distinctly different seasonal patterns of rotavirus disease in some countries with similar geographic location, climate and level of development indicate that a single unifying explanation for variation in seasonality of rotavirus disease is unlikely.

Conclusion: While no unifying explanation emerged for varying rotavirus seasonality globally, the country income level was somewhat more predictive of the likelihood of having seasonal disease than other factors. Future evaluation of the effect of rotavirus vaccination on seasonal patterns of disease in different settings may help understand factors that drive the global seasonality of rotavirus disease.

Figure 1

Seasonal variation in rotavirus prevalence globally by region, 1996–2009.

Figure 2

Seasonal variation in rotavirus prevalence globally by latitude, 1996–2009.

Figure 3. Timing of the primary peak of rotavirus disease globally, by latitude

Colors denote continents to which each point belongs and size of circle is proportion to the number of months rotavirus was in circulation.

Figure 4. Amplitude of the primary peak of the seasonal signature of the series as a function of latitude

Amplitude is peak-trough/peak ratio. Colors denote continents to which each point belongs.

Figure 5

Map with the same information, but here the relative amplitudes are expressed in circle sizes.

Figure 6. Seasonal variation in rotavirus in tropical and northern temperate zones, by World Bank income groups

We restricted the analysis to studies conducted in the Northern Hemisphere and the tropical belt (i.e., latitudes 10° North and 10° South of the equator) to avoid falsely representing seasonality by summing monthly prevalence across regions with peak rotavirus detections during opposing seasons (which would result in a bias towards weaker seasonality).

Figure 7. Scatter plot of gross national income per capita plotted against the strength of rotavirus seasonality

Gross national income per capita is adjusted for purchasing power parity. Strength of seasonality was defined by the “seasonality ratio” (peak/mean prevalence). Colors denote continents to which each point belongs. Site legends are displayed for “outliers” (where values are more than one standard deviation above the average).

Figure 8

Seasonality in low and low-middle income countries, by latitude.

Figure 9

Seasonality in high-middle and high-income countries, by latitude.

Figure 10. Visualization of relative detection of rotavirus per month in each site globally, sorted by latitude

The colors represent the monthly prevalence of rotavirus among diarrhea cases, as indicated by the color bar.