Ensuring the Vital Role of Sanitation in Disease Prevention

We frequently take sanitation for granted in the United States; however, roughly 2.4 billion individuals around the world lack access to adequate sanitation, and nearly 1 billion practice open defecation. In response to these startling numbers, researchers from Emory University, the World Health Organization (WHO), Imperial College London, Ludwig Maximilian University of Munich, and the London School of Hygiene & Tropical Medicine, released a new meta-analysis regarding the impact of sanitation on infectious disease transmission and nutritional status.

The study is currently in press, but will be published shortly in the International Journal of Hygiene and Environmental Health. Led by Matthew Freeman, PhD, MPH, the researchers sought to review evidence regarding the impact of sanitation on diarrhea, soil-transmitted helminth (STH) infections, trachoma, schistosomiasis, as well as nutritional status that was assessed through anthropometry (comparative analysis of human body measurements through size, weight, and proportions of the human body).

The number of deaths that occur every year because of some of these ailments is astounding—1.4 million deaths are due to diarrhea alone. Trachoma is the leading infectious cause of blindness in the world, leaving 1.2 million irreversibly blind, and roughly 142 million children have stunted growth around the world. Over 1 billion individuals are at risk for STH infections, which are the result of parasite nematodes that spread through fecal contamination. Despite sanitation being a primary barrier for most of these illnesses, 2.4 billion individuals lack the most basic access to adequate sanitation, such as pit latrines.

In response to these overwhelming relationships, the researchers wanted to perform a meta-analysis to truly show that the role that sanitation has in health and nutrition is imperative. They looked at studies with outcomes of diarrhea, STH infections, schistosomiasis, trachoma, and nutritional status, as well as experimental and observational studies that analyzed the impact of sanitation on these ailments. To ensure compatibility, they used the most adjusted results (in cases that had both adjusted and unadjusted results) regarding the efficacy of sanitation on the outcome of each of the diseases studied. They compared the overall impact of sanitation by pooling the primary effect estimates and utilized forest plots to show the point estimates and confidence intervals for each study. Moreover, they used a sanitation ladder to study the different types of sanitation, which ranged from open defecation to improved sanitation. Lastly, they assessed the quality of evidence from intervention studies through a GRADE approach (Grading of Recommendations, Assessment, Development, and Evaluation), which scores intervention studies from high quality to low (and includes moderate).

After reviewing 10,485 studies, they narrowed it down to 64 studies that met their criteria for inclusion, but also added 107 studies that were previously used in meta-analyses. Upon review, they found some fascinating revelations regarding sanitation on each of the outcomes. For diarrhea, 33 studies were reviewed, and they found that sanitation was associated with 13% lower odds of diarrhea. They also found that community-led sanitation (CLTS) and hand hygiene actions were successful. Despite this analysis, the quality of the evidence from the interventional studies was quite poor in terms of making the case for sanitation interventions impacting diarrhea. For STH infections, the 65 studies found that the evidence for impact of sanitation on several of the STH organisms was very low. Forty-six studies met criteria for assessment of trachoma, a majority of which found that sanitation was associated with lower odds of active trachoma. For schistosomiasis, 30 studies were assessed, but no intervention studies were found, so, while some studies showed lower cases linked to sanitation, none were interventional. Lastly, researchers looked at nutritional status via 17 studies which linked sanitation with better weight scores; however, there was moderate evidence from intervention studies regarding the impact of sanitation on stunting and low weight.

This extensive meta-analysis shows that despite the overwhelming impacts and vital role of sanitation on health, there are significant gaps within research and literature to support it. While sanitation was found to be protective for all the outcomes, the evidence was considered poor, and the scores for intervention studies showing correlation were also poor. Through their study, they found gaps in research and evidence which underscores the need for additional intervention studies that focus on the impact of these efforts, and how to implement sanitation improvements.