This study aimed to examine the previously unknown long-term spatio-temporal patterns in diarrheal morbidity and mortality across age groups and geography in Brazil under the light of evolving socioeconomic factors and interventions.

Nationwide mortality (1979–2014) and hospitalization (1998–2014) data were obtained from the Brazilian Ministry of Health. Analyses of long-term secular trends and seasonality of diarrheal morbidity and mortality were performed in EPIPOI (www.epipoi.info).

For most states, the primary peak in mortality risk among children under 5 years occurred from December–April (summer/early autumn) from 1979–1988. From 2000–2005 (before the 2006 implementation of rotavirus vaccination), the pattern switched to June–October (winter/early spring). By 2007–2014, the peak in mortality shifted back towards summer/early autumn. A similar pattern was observed for hospitalizations. These patterns were particularly apparent in non-equatorial regions of the country. In contrast, the risk of diarrhea-related death among older children (5–19 years) did not demonstrate well-defined seasonality or spatial patterns.

Rotavirus vaccination policies were associated with a shift in the timing of seasonal peaks in children under 5, reminiscent of the summer diarrhea period common decades prior. Additionally, young children were shown to have distinct disease patterns compared to other age groups, suggesting different etiologies.