Severe droughts and the tuberculosis and HIV care cascade in the Brazilian Amazon: a Bayesian, structural, interrupted time-series analysis of 24 years of surveillance data

Background

In river-dependent regions such as the Brazilian Amazon, severe droughts can disrupt care continuity by isolating municipalities and fragmenting supply chains. We assessed how four major droughts affected tuberculosis and HIV care cascades in Amazonas state.

Methods

We analysed monthly data (Jan 1, 2001, to Dec 31, 2024) from all 62 municipalities of the Amazonas state, Brazil, grouped into nine river basins and stratified by sex when available. Droughts were defined by the relative maximum cumulative water deficit value being below −2·0 or river discharge at or below the fifth historical percentile. We prespecified four major drought episodes affecting Amazonas at a monthly resolution: May to June, 2005; May to June, 2010; August, 2015, to April, 2016; and October, 2023, to February, 2024. Outcomes were primary-care consultations, tuberculosis and HIV notifications, treatment interruption, and disease-specific mortality. Additionally, we did a prespecified subgroup analysis stratified by sex for both diseases’ indicators to assess whether drought-associated deviations differed systematically between men and women. We fitted Bayesian hierarchical negative binomial models to estimate counterfactual trajectories and summarised effects as incidence rate ratios (IRRs) and excess events per 100 000 population.

Findings

The 2015–16 drought coincided with widespread consultation deficits (statewide peak IRR 0·78 [95% credible interval 0·68–0·89]) and pronounced increases in HIV treatment interruption across all basins (statewide peak IRR 6·01 [2·12–15·33]), particularly among men (Rio Negro peak IRR 5·57 [3·02–9·78]). By contrast, the 2023–24 drought coincided with increased care consultations statewide (peak IRR 1·63 [1·25–2·11]) but persistent treatment interruption and mortality signals, including female-predominant increases in HIV treatment interruption in Rio Negro (peak IRR 2·87 [1·27–5·63]) and female mortality statewide (1·97 [1·05–3·39]), with additional basin-level mortality increases in Alto Solimões, Baixo Amazonas, and Médio Amazonas. Tuberculosis notifications increased mainly in 2023–24 in specific basins, especially in Baixo Amazonas (peak IRR 2·09 [1·54–2·76]), Médio Amazonas (1·74 [1·30–2·28]), and Baixo Solimões (1·60 [1·24–2·07]).

Interpretation

Severe droughts were associated with basin-specific disruptions in tuberculosis and HIV care cascades in the Brazilian Amazon, with clearer signals in adherence-dependent and downstream outcomes than in case detection. Strengthening resilience will require anticipatory, continuity-focused strategies that safeguard treatment access during climate-related transport constraints.