Estimating risk of intestinal nematode infection from exposure to ambient waters using quantitative microbial risk assessment (QMRA) in Salta, Argentina

ARTI KUNDU; HUGO R. POMA; VERÓNICA B. RAJAL; STEFAN WUERTZ

Florianópolis

Simposio; 17th International Symposium on Health Related Water Microbiology - Watermicro 2013; 2013

Aims The main objectives of this research were to establish risks related to (i) direct or indirect incidental ingestion of water in Arenales river in three scenarios: primary contact, children and secondary contact; (ii) consumption of uncooked vegetables irrigated with A. lumbricoides contaminated water; and (iii) accidental ingestion of irrigated water by farmers working in the fields. Methods The study area focused on the Arias-Arenales river, which is in the northwestern region of Salta province in Argentina. Eleven locations on the Arenales river were selected for a thirteen-month monitoring study (Figure 1). Laboratory Methodology Twenty-liter samples were concentrated to 50-70 mL of retentate using hollow fiber ultrafiltration. The eluted samples were carefully passed through three layers of gauge to remove foreign particles and preserved in different solutions as previously mentioned (Poma et al., 2012). Finally, helminth eggs were identified by direct microscopic examination (1000X). Human Health Risk Assessment Approach A quantitative microbial risk assessment (QMRA), based on observed nematode density, was performed to calculate the annual probability of helminth infection in various scenarios associated with direct or indirect exposure to Ascaris lumbricoides in surface waters. Ascaris was chosen as the specific hazard in the risk assessment model for the following reasons: (1) Ascaris is very prevalent in most parts of the world, especially in low- and middle-income countries; (2) Ascaris eggs are the most hardy and resistant of all excreted pathogens; and (3) they can survive in the environment for periods of months or even years. The eggs need small quantities of oxygen for development but can remain viable for long periods in anaerobic conditions (Feachem et al., 1983). Exposure assessment helps in the assessment of scenarios through which humans come in contact with the pathogen present in the environment, through ingestion of contaminated water, body contact with polluted recreational water, or through consumption of vegetables irrigated by polluted freshwater. We modeled three scenarios: direct or indirect ingestion of surface water, consumption of uncooked raw vegetables, and risk from use of polluted surface water in irrigating crops by the people working in the fields. In the first scenario, the river water is used for recreational purposes. The primary activities can be divided into three categories based on the degree of water exposure ? primary contact by adults, primary contact by children, and secondary users irrespective of age. In the second scenario, the four different vegetables (lettuce, cucumber, broccoli and cabbage) were considered to estimate risks associated with consumption of raw vegetables irrigated with surface water. In the last, we looked at the risk of intestinal infection in people working in the fields and using surface water for irrigation purposes. Results The highest estimated mean risk from direct or indirect ingestion of surface water per person per year (pppy) from a single exposure scenario was found in children (21.23%), followed by adults (12.49%) and secondary exposure (1.54%). We estimated the mean annual risks from consumption of raw (uncooked and unpeeled) vegetables irrigated with polluted water as a worst case scenario. The mean risk was highest in lettuce (0.659%) and lowest in cucumber (0.011%) for the total population. A similar pattern was found for the consumer-only population as well. Here, the risks from consumption of vegetables were 0.27% for cucumbers and 1.54% for lettuce. The annual risk of infection in farmers due to accidental ingestion of irrigated water was 1.06%. The risk varied from as low as 0.005% to a high value of 41% in farmers working in the field without using any protective clothing like gloves, rain boots and so forth. We also estimated risks associated with four scenarios for treating left-censored observations: (i) one-half the detection limit (DL) was assumed for the censored data; (ii) DL was assumed for censored data; (iii) bounding for the censored observations; and (iv) observations with zeroes. Conclusions ? Children are the most vulnerable group and had the highest risk from incidental ingestion of ambient waters (21.23%), according to the US EPA acceptable level for freshwaters (0.8%). ? Intestinal nematode infection risk was highest from consumption of uncooked raw lettuce irrigated with contaminated surface water among different vegetables considered for risk assessment. ? People working in the fields are highly susceptible to Ascariasis infection and should safeguard themselves by using protective clothing. ? Risk distributions were similar for the three scenarios for left-censored data (DL, half-DL and zeroes) but one order of magnitude lower in the bounding scenario. ? Active surveillance measures should be followed to monitor and improve the surface water quality with the aim of reducing the risk of infection from enteric pathogens and improving public health and quality of life in the population. Figures Fig. Monitoring locations along the Arenales river in Salta, Argentina are indicated by squares. References Poma, H.R., Cacciabue, D.G., Garce, B., Gonzo, E.E. and Rajal, V.B., 2012. Towards a rational strategy for monitoring of microbiological quality of ambient waters. Science of the Total Environment 433, 98-109. Feachem, R.G., Bradley, D.J., Garelick, H. and Mara, D.D., 1983. Sanitation and disease:Health aspects of excreta and wastewater management. John Wiley &Sons.