Higher helminth ova counts and incomplete decomposition in sand-enveloped latrine pits in a coastal sub-district of Bangladesh

Abstract

Pit latrines are the most common latrine technology in rural Bangladesh, and untreated effluent from pits can directly contaminate surrounding aquifers. Sand barriers installed around the latrine pit can help reduce contamination but can also alter the decomposition of the fecal sludge and accelerate pit fill-up, which can counteract their benefits. We aimed to evaluate whether there was a difference in decomposition of fecal sludge and survival of soil-transmitted helminth (STH) ova among latrines where a 50-cm sand barrier was installed surrounding and at the bottom of the pit, compared to latrines without a sand barrier, in coastal Bangladesh. We assessed decomposition in latrine pits by measuring the carbon-nitrogen (C/N) ratio of fecal sludge. We enumerated Ascaris lumbricoides and Trichuris trichiura ova in the pit following 18 and 24 months of latrine use. We compared these outcomes between latrines with and without sand barriers using generalized linear models with robust standard errors to adjust for clustering at the village level. The C/N ratio in latrines with and without a sand barrier was 13.47 vs. 22.64 (mean difference: 9.16, 95% CI: 0.15, 18.18). Pits with sand barriers filled more quickly and were reportedly emptied three times more frequently than pits without; 27/34 latrines with sand barriers vs. 9/34 latrines without barriers were emptied in the previous six months. Most reported disposal methods were unsafe. Compared to latrines without sand barriers, latrines with sand barriers had significantly higher log₁₀ mean counts of non-larvated A. lumbricoides ova (log₁₀ mean difference: 0.35, 95% CI: 0.12, 0.58) and T. trichiura ova (log₁₀ mean difference: 0.47, 95% CI: 0.20, 0.73). Larvated ova counts were similar for the two types of latrines for both A. lumbricoides and T. trichiura. Our findings suggest that sand barriers help contain helminth ova within the pits but pits with barriers fill up more quickly, leading to more frequent emptying of insufficiently decomposed fecal sludge. Further research is required on latrine technologies that can both isolate pathogens from the environment and achieve rapid decomposition. Conventional pit latrines do not fully isolate fecal pathogens and in many settings, pits are emptied manually, and pit contents released into water bodies and fields. Sand barriers installed around the latrine pit can help reduce contamination but can also alter the decomposition of the fecal sludge. We evaluated whether a sand barrier effectively contains STH ova within the pit and whether it alters the decomposition processes of pit contents and/or accelerates pit fill-up. C/N ratio was significantly higher in latrines without a sand barrier and approached the preferable range for optimal decomposition. Pit latrines with sand barriers filled up more rapidly and were emptied more often. No households in either arm used any protective measure when emptying the pits. Larvated STH ova counts were similar in the latrines with vs. without sand barriers while non-larvated ova counts were higher in pits with a sand barrier. The lower C/N ratio and quicker filling up of latrines with sand barriers indicate that pit contents are more likely to be infective at the time of pit emptying, necessitating safe emptying and disposal methods. Latrines with and without sand barrier had similar loading into the pit by infected individuals. Enveloping latrine pits with a sand layer helped contain helminth ova within the pits, allowing time for them to become non-viable and potentially reducing the spread of viable ova into the surrounding environment.