Case Study 6: Yamuna River
Team Members: Verbyla, M., Hyoung Lee, W., Li, Q., Prasad, S., Zhang, W.
- The Problem
- Hazard ID
- Exposure Assessment
- Dose Response
- Risk Characterization
- Risk Management
The objective of this case study is to assess microbial risks from a stream “AA” eventually discharging water to the Yamuna River (Delhi, India). The AA stream is mostly polluted with domestic wastewater and surface runoff from a village “BB”. Due to lack of water quality monitoring and treatment infrastructure, this village measures only total coliforms and fecal coliforms in wastewater effluent and in the stream “AA”.
Year 2010 microbial quality data for this stream was: total coliforms: 2*109 ±1*102MPN/100 mL and fecal coliforms=1.5*107±8*102 MPN/100 mL (average ±one standard deviation) (samples =10). The stream water is generally used for (1) drawing source drinking water from a location 5 Km downstream from discharge point (for another village “DD”), (2) recreational bathing activities (twice per week for May to August month) and (3) agricultural bed farming (mainly spinach and cucumber). Agricultural produce is mostly consumed in the village only.
The goal was to estimate bacterial risks of infection annually for villagers of village “BB” using all possible combinations of given activities in a year.
Vibrio cholera is a comma-shaped, gram-negative aerobic or facultatively anaerobic bacillus that varies in size from 1-3 µm in length by 0.5-0.8 µm in diameter. The natural dissemination is through fecal contamination of food or water supply. The clinical effect is profuse watery diarrhea and severe V. Cholera can cause dehydration, hypovolemic shock, and death within hours of onset (Medscape). The incubation times are 4 hours to five days with an average of 2-3 days (Arizona Department of Health Services). If appropriately treated the mortality rate is less than 1%. However, if untreated the mortality rate may exceed 50%. Seasonality (e.g., floods, droughts, temperature and biotic interactions) can affect the secondary transmission (Codeco, 2001) and Cholera cases increase and peak with a lag after the summer monsoons, as floods presumably concentrate the population on the decreased land area available and break down sanitary conditions, promoting secondary transmission through the more direct fecal–oral route (Koelle et al., 2005). V. Cholera can survive up to 24 hours in sewage as long as six weeks in water containing organic matter and also withstand freezing for 3 to 4 days.
Shigella sp. is a genus of gram-negative, facultative anaerobic, nonspore forming, non-motile, rod-shaped bacteria closely related to Salmonella. The disease is transmitted faeco-orally, the commonest modes being person-to-person contact and contaminated food and water (Sur et al., 2004). Infected food handlers can spread the disease (Sur et al., 2004). The disease symptom ranges from mild diarrhea to severe dysentery with frequent passage of bloody, mucoid, small-volume stools (Hale 1991). Shigella may also cause destruction of colon epithelium resulting in acute colitis (Takeuchi et al., 1968). Incubation period of the disease is 1-4 days which is usually followed by sudden onset of acute symptoms (Sur et al., 2004). The overall mortality rate in developed countries is less than 1%. In the Far East and Middle East, the mortality rates for S dysenteriae infections may be as high as 20-25%.(Medscape). For the excretion rates, an infected person excretes the organisms in the stool and this can extend up to 4 weeks from the onset of illness (Sur et al., 2004). Shigella infections are recognized in persons attending mass outdoor gatherings, the singular importance of handwashing in reducing secondary transmission of shigellosis, and the potential for explosive outbreaks when communal meals are prepared by large numbers of food handlers (Lee et al., 1991). Secondary transmission of S. sonnei often exceeds 30% in households with young children (shane et al., 2003).
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions (Wikipedia). Salmonella are usually transmitted to humans by eating foods contaminated with animal feces (e.g., by ingestion of bacteria in contaminated food or water). Contaminated foods usually look and smell normal (CDC). However, direct contact with animal and human carriers has also been implicated (Medscape).For example, laundry personnel suggested secondary transmission (Standaert 1994). Diarrhea, fever, and abdominal cramps are common indicators of Salmonella infection. However, as these symptoms are common to most enteric infections, laboratory tests of stool samples (i.e., determining that Salmonella is the cause of the illness) are necessary for proper diagnosis (CDC). Incubation period is a few hours to one day (Wikipedia) Twenty percent of patients require hospitalization, with an estimated death rate of 0.6% (Weinberger and Keller, 2005). Infection with drug-resistant nontyphoid Salmonella and Salmonella typhi increase the likelihood of hospitalization and death (Weinberger and Keller, 2005). Invasive nontyphoid Salmonella infection occurs in about 5% of cases in Israel (Weinberger and Keller, 2005) and is responsible for 400-600 deaths in the United States each year (Linam and Gerber, 2007). In 2010, the CDC reported Salmonella infection was the most common foodborne disease in the United States and was associated with the most hospitalizations and deaths (CDC, 2011). Mortality for nontyphoid Salmonell a is reported to be as high as 60% in African patients with HIV (Boyle et al., 2007). Mycotic abdominal aortic aneurysms are more common in immunocompromised and HIV patients. Treated typhoid cases have a 2% mortality rate with a 15% relapse rate (Chambers et al., 2008). A significant number of typhoid patients become chronic asymptomatic carriers and can shed high numbers of bacteria in the stool for a lifetime without obvious symptoms (Boyle et al., 2007). Depending on the serotype, roughly 1% of adults and 5% of children excrete organisms for greater than a year (Heymann, 2004). Attack rates are highest in persons younger than 20 years or older than 70 years. The highest rate is found in infants (130 isolates/100,000). One quarter to one third of pediatric typhoid patients are younger than 5 years, of which 6-21% are younger than 2 years (Zaki and Karande, 2011). Neonates are at a greater risk to fecal-oral transmission secondary to relative decreased stomach acidity and buffering of ingested breastmilk and formula. Elderly persons are at a relative greater risk to infection secondary to chronic underlying illness and weakened immunity. Nursing home residents have a particularly higher risk. The case-fatality rate (CFR) is estimated at 1.3% for nontyphoid Salmonella for those age 50 years or older (Medscape).
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|Agent strain||Best fit model||Optimized parameters||LD50/ID50||Host||Route||Dose units||endpoint|
|Salmonella anatum||β-Poisson||α=3.18E-01, N50=3.71E+04||3.71E+04||human||oral, with eggnog||inferred MPN/ml||positive stool culture|
|Salmonella meleagridis||β-Poisson||α=3.89E-01 , N50=1.68E+04||1.68E+04||human||oral, with eggnog||inferred MPN/ml||infection|
|Salmonella Typhi||β-Poisson||α=1.75E-01, N50=1.11E+06||1.11E+06||human||oral||inferred MPN/ml||disease|
|Shigella flexneri||β-Poisson||α= 2.65E-01, N50=1.48E+03||1.48E+03||human||oral(in milk)||inferred MPN/ml||positive stool isolation|
|Vibrio cholerae||β-Poisson||α= 2.50E-01, N50=2.43E+02||2.43E+02||human||oral (with NaHCO3)||inferred MPN/ml||infection|
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