Health Risks for Sanitation Service Workers along a Container-Based Urine Collection System and Resource Recovery Value Chain

Abstract

Container-based sanitation (CBS) within a comprehensive service system value chain offers a low-cost sanitation option with potential for revenue generation but may increase microbial health risks to sanitation service workers. This study assessed occupational exposure to rotavirus and Shigella spp. during CBS urine collection and subsequent struvite fertilizer production in eThekwini, South Africa. Primary data included high resolution sequences of hand-object contacts from annotated video and measurement of fecal contamination from urine and surfaces likely to be contacted. A stochastic model incorporated chronological surface contacts, pathogen concentrations in urine, and literature data on transfer efficiencies of pathogens to model pathogen concentrations on hands and risk of infection from hand-to-mouth contacts. The probability of infection was highest from exposure to rotavirus during urine collection (∼10^-1) and struvite production (∼10^-2), though risks from Shigella spp. during urine collection (∼10^-3) and struvite production (∼10^-4) were non-negligible. Notably, risk of infection was higher during urine collection than during struvite production due to contact with contaminated urine transport containers. In the scale-up of CBS, disinfection of urine transport containers is expected to reduce pathogen transmission. Exposure data from this study can be used to evaluate the effectiveness of measures to protect sanitation service workers.

Figure 1

Urine volume measured on hands during struvite production from a tracer study. (a) Urine was augmented with dye and study participants wore cotton gloves over latex gloves during struvite production. (b) Cotton gloves were extracted in distilled water to measure the volume of urine exposure spectrophotometrically. (c) Five batches of struvite (A through E) were produced for the study. For each struvite batch produced, the average (±SD) volume of urine that contacted left and right hands for two study participants is presented.

Figure 2

Simulated rotavirus concentration on hands for left (A) and right (B) hands with corresponding dose events (bottom) for one person-day (person 3, day 2) monitored during urine collection. Dark lines (A and B) represent median simulations; dotted lines (A and B) represent fifth and 95th percentile simulations. Open circles (C and D) represent median dose, with the error bars representing the fifth and 95th percentile simulation values.

Figure 3

Risk of infection from a single exposure (top) and from cumulative exposures throughout the period of time when video was captured (bottom) during struvite production (left) and urine collection (right). Dots represent median risk. Error bars represent the upper and lower 95th percentile simulations. Dashed gray line represents risk of 10^–4 infections, which is the U.S. EPA recommended tolerable disease burden per person per year.

Figure 4

Linear correlation between (Y-axis) rotavirus and (X-axis) Shigella spp. for simulated hand-to-mouth contacts for (A) dose and (B) infection risk during (black diamond) struvite production and (gray dot) urine collection. Each point represents the median instantaneous dose modeled for each study participant. Horizontal and vertical error bars represent the 95% confidence intervals of the modeled doses. Infection risk is higher than (dotted line) U.S. EPA tolerable disease burden of 10^–4 infections per person per year for both rotavirus and Shigella spp.