Spatiotemporal hotspots of neonatal and child mortality in Nyeri County, Kenya, 2018–2025

Abstract Background Understanding the spatial and temporal distribution of under-five mortality is critical for targeting public health interventions. County-level estimates may mask important local variations and fail to identify persistent mortality hotspots. This study examined whether under-five mortality in Nyeri County, Kenya, was spatially clustered, whether hotspot patterns differed by age group, and how mortality trends varied between hotspot and non-hotspot wards. Methods We conducted a retrospective ecological spatio-temporal analysis using annual ward-level mortality data for children aged 0–59 months in Nyeri County from 2018 to 2025. Mortality data from the Kenya Health Information System were categorized into neonates (0–28 days), infants (1–11 months), and children (12–59 months). Ward-level death counts were linked to population denominators and geographic data. A retrospective space-time Poisson scan statistic in SaTScan identified significant mortality clusters using 999 Monte Carlo replications. Annual mortality maps were generated, and mortality trends were compared between hotspot and non-hotspot wards. Results Under-five mortality was concentrated in a few wards rather than evenly distributed across the county. The primary cluster included Ruring’u, Kiganjo/Mathari, and Rware wards, with 747 observed deaths versus 199.8 expected deaths (RR = 5.82; p < 0.001). Additional clusters were identified in Magutu, Iriaini, and Karatina Town wards (RR = 3.33; p < 0.001) and in Iria-ini ward alone (RR = 2.05; p = 0.008). Significant clustering occurred across all age groups, with the strongest effect among neonates, where the primary cluster recorded 692 observed versus 142 expected deaths (RR = 9.29; p < 0.001). Annual under-five mortality increased from 229 deaths in 2018 to 289 in 2021 before declining to 118 in 2025. Hotspot wards consistently experienced higher mortality rates than non-hotspot wards. Conclusions Under-five mortality in Nyeri County was spatially concentrated and temporally dynamic, with persistent hotspots across age groups. These areas should be prioritized for mortality audits, strengthened surveillance systems, and targeted interventions to improve neonatal, infant, and child health outcomes.