Outbreak of Disease in Yellowbourne - Case Study Example

Outbreak of disease in Yellowbourne: A Report Introduction Infectious diarrhoeal diseases occur worldwide and are the cause of 3.5% of all deaths and 4% of health loss due to disability in a year (UN Report, 2003, p.104). Children are more prone to acute gastrointestinal symptoms, and approximately 1.8 million children die from diarrhea, annually, all over the world (WHO Report, 2008). Contaminated drinking water is one of the major routes of transmission of waterborne diseases such as diarrhoea. While faeces are often the source of contamination, various infectious agents (bacterial, viral or parasitic) are implicated in the aetiology of diarrhoea (Cutting, 1988). Microbial indicators are useful tools for identifying faecal contamination. Total and faecal coliforms have been used extensively for many years for the purpose of confirming faecal contamination. However, in recent years, several limitations in the utility of the coliforms as indicators of faecal pollution have been unravelled by scientists leading to additional microbes ( e.g., E. coli, enterococci, and Clostridium perfringens as well as viruses) being suggested for use as alternative indicators (Griffin et al., 2001). The enterococcus group is a subgroup of the faecal streptococci that includes at least five species and enterococci have been used successfully as indicators of faecal pollution (Cabelli et al., 1982). "Indicator organisms are useful in that they circumvent the need to assay for every pathogen that may be present in water. Ideally, indicators are nonpathogenic, rapidly detected, easily enumerated, have survival characteristics that are similar to those of the pathogens of concern, and can be strongly associated with the presence of pathogenic microorganisms" (Scott et al., 2002). Understanding the origin of faecal pollution is vital both for assessing associated health risks and initiating necessary remedial actions while the problem exists as it is well established that the majority of the contaminating organisms are not limited to humans but also exist in the intestines of many other warm-blooded animals (Orskov and Orskov, 1981). To meet the challenge of identifying sources of faecal pollution, various microbiological methods have been proposed, one of them being the determination of the ratio of faecal coliforms to faecal streptococci. The advantages of using this method are that the assay requires minimal expertise to perform while being able to provide rapid results (Clesceri et al., 1998). This is a report of the Public Health Investigation into the outbreak of diarrhoea in Yellowbourne during April - May, 1997. Background The outbreak of diarrhoea commenced in Yellowbourne on 18 April, 1997 when the first case, a 24 year old male, took ill with symptoms of watery diarrhoea. He was admitted to the local hospital the next day, i.e., on the evening of 19 April, 1997 for rehydration and medical care. Three days later, on 22 April 1997, 3 more patients suffering from watery diarrhoea received treatment from a G.P. One of the patients, a young child, was severely dehydrated, and the G.P immediately had him admitted to a regional hospital. The number of cases escalated over the next few days and the local Environmental Health department was alerted. In all, 182 people were affected. Common symptoms reported included fever, nausea, loss of appetite as well as watery diarrhoea. The town of Yellowbourne has a population of 157,460. Methods Data pertaining to the potential source of illness were collected by the Environmental Health department through visits to or telephoning each adult patient. In the case of children under 18 years of age, the information was obtained from their parents. Faecal samples were collected and sent for analyses of pathogenic organisms at the microbiology department of Yellowbourne hospital. The tests were repeated by specialists at reference laboratories. The potable water supply system as well as the area of its location were investigated. The water supply network consists of a pipe carrying water from the treatment plant to a storage tank located at the bottom of a steep embankment. The distribution pipe carries the water from the storage tank into the town of Yellowbourne. Water samples obtained from different points in the supply network were analysed for the biomass levels of indicator organisms of faecal origin. On the 26th April, 1997 the water distribution system was minutely inspected. The crack noticed in the storage tank was repaired. Subsequently, the tank was thoroughly flushed and chlorinated. The area surrounding the storage tank was investigated and the weather conditions noted. Results A total of 182 people, that is, 1 person in every 1000 of the town's population, got affected by the outbreak of diarrhoea in Yellowbourne in the spring of 1997. Two cases were acute and required hospitalisation. The disease continued to rage for a little over a month. The time course of the outbreak is shown in Figure 1. The outbreak peaked around day 5 and started to abate only after 2 weeks. Age-wise, statistics showed (Table 1) that infants and children in the age group of 0-5 years were the worst affected. A high proportion ('10%) of the children amongst the victims attended the same nursery, Calcote. Investigations by the Environment Health department indicated that the outbreak of diarrhoea could not have been caused by food-borne pathogens since those who had become ill did had not have common food outlets. Therefore, the disease must have been water-borne. According to Strauss et al., "total coliform is a non-specific indicator of faecal contamination and can originate from a number of different plant and soil sources. Faecal coliform represents a more specific indicator of fecal contamination, however, it does not specifically quantify Escherichia coli (E. coli), the most common coliform inhabiting the intestinal tract"(2001). Indeed, the potable water supplied to Yellowbourne from the storage tank was found to contain exceedingly high levels the indicator organisms. As shown in Table 2, the biomass levels determined 10 days after the outbreak were: total coliforms (120/100ml), faecal coliforms (36/100ml) and faecal streptococci (260/100ml). Although the crack in the storage tank was discovered on the 26 April, remedial measures taken to repair and rehabilitate the tank were completed only around the 3 May as indicated by the sudden abatement in the number of cases being reported (Fig.1). Coliform bacteria are common in the environment and are generally not harmful. "However, the presence of these bacteria in drinking water is usually a result of a problem with the treatment system or the pipes which distribute water, and indicates that the water may be contaminated with germs that can cause disease. Faecal coliform and E. coli are bacteria whose presence indicates that the water may be contaminated with human or animal wastes. Microbes in these wastes can cause short-term effects, such as diarrhea, or other symptoms.'[U.S. Environmental Protection Agency (EPA)]. However, the faecal coliforms are rapidly eliminated by chlorinating the water as shown in Fig.2. The source of contamination was animal faeces and not human faeces. This was apparent from the comparative levels of the two indicator organisms, faecal coliforms (FC) and faecal streptococci (FS) observed in the supplied water. For instance, the levels of the two bacterial species were, respectively, 36 and 260 in the water from the storage tank (Table 2). Historically, the FC/FS ratio has been used to determine if pollution is of human or animal origin. According to Geldreich and Kenner (1969), faecal coliforms are more numerous than faecal streptococci in human faeces with a FC/FS ratio always greater than four. Conversely, FS are more numerous than FC in animal faeces with the FC/FS ratio always Read More