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| ISBN-13: | 9780854046263 |
|---|---|
| Publisher: | RSC |
| Publication date: | 11/27/2002 |
| Pages: | 490 |
| Product dimensions: | 6.14(w) x 9.21(h) x (d) |
Read an Excerpt
Case Studies in Food Microbiology for Food Safety and Quality
By Rosa K. Pawsey
The Royal Society of Chemistry
Copyright © 2002 The Royal Society of ChemistryAll rights reserved.
ISBN: 978-0-85404-626-3
CHAPTER 1
Water as a Vector of Organisms
Key issues
• Water
• Vibrio cholerae
• Microbial growth and survival in water
• Food safety control, and the need for national infrastructure
Challenge
In 1974, cholera spread in Portugal. Not only did potable water supplies become polluted with cholera infected faeces, but so did shellfish and other foods and bottled water. This case study invites you to start thinking about how organisms become disseminated, whether they die in that process, and what affects their growth and survival. You can, of course, extend your thoughts beyond this case and wonder how control systems prevent water in all its various uses in the food industry both becoming contaminated and being a vector for a very wide range of pathogens.
1.1 THE CASE STUDY: CHOLERA IN PORTUGAL, 1974
(Most of the text below comes from Blake et al., (1977a and 1977b, see 1.1.4). The text in the original papers has been slightly shortened and some linking sentences put in to allow textual flow. Paragraphs from the two papers have been mixed to provide a shorter version of the two texts which are used here with the permission of the copyright holders – The Johns Hopkins University School of Hygiene and Public Health.
From Blake et al., 1977a:
On April 24,1974, in Tavira, a town on the southern coast of Portugal, a 33-year old man developed diarrhoea and dehydration so severe that he suffered a cardiac arrest. An alert physician suspected cholera, and the Ricardo Jorge Institute in Lisbon isolated Vibrio cholerae biotype El Tor serotype Inaba from his stool. V. cholerae were subsequently isolated from a Lisbon woman who had contracted a diarrheal illness on May 10 and from a child in Porto on May 14. Within six weeks after the first case, cholera had been reported from eight of Portugal's 18 districts. Eventually 17 of the 18 districts reported cholera, all due to El Tor Inaba organisms. The epidemic peaked in the last week in August, then declined rapidly; on November 29, 1974, Portugal was declared free of cholera. In this seven month period 2467 cases and 48 deaths were reported to the World Health Organisation (WHO). The case-fatality ratio was 1.9%.
Control measures included individual case investigations by public health nurses, distribution of two- or three-day supply of tetracycline to all contacts of cholera patients, a massive health education program, and an extensive effort to promote the chlorination of public water systems. These measures were supplemented by distribution of free bottles of chlorine for disinfection of drinking water from unsafe sources. Cholera vaccine was given only to those who demanded it.
Investigators from the Center for Disease Control [USA] and the Portuguese Directorate General of Health carried out two studies in Tavira and Faro, two cities on the southern coast, and in Lisbon to determine the important modes of transmission of cholera in Portugal.
1.1.1 Background to the Outbreak
Both Tavira and Faro are separated from the open sea by the Ria de Faro, a complex of islands and mud flats that extends approximately 50 km along the southern coast [of Portugal]. Sewage from the coastal towns emptied into the Ria, and water and shellfish in the Ria had high coliform bacteria counts. Most shellfish consumed throughout Portugal are caught in this area. After anecdotal information suggested that shellfish had caused some cases of cholera, the Maritime Biology Institute in Faro systemmatically cultured water and shellfish from the Ria from May to August 1974; V. cholerae was isolated from 24% of 121 seawater samples and 42% of 154 shellfish, including clams (44 of 114 positive), cockles (11 of 22), oysters (7 of 15), and mussels (2 of 3).
Tavira's municipal water supply was chlorinated, but some residents preferred to drink from two springs in the town. One of these, the Fonte do Bispo, emerged from a pipe in a populated area and had allegedly produced clear water until September 1973 when, following blasting of the rock above the spring and a heavy rain, the water was muddy for a few days. Both springs were closed on May 10 and 11, shortly after the cholera outbreak began, because health authorities suspected that some of the cases might have resulted from drinking from these springs. No water from either spring was cultured. Troops travelled back and forth between a military base uphill from the Fonte do Bispo and what were then Portugal's African colonies – Angola, Mozambique and Portuguese Guinea. Untreated sewage from the base and the town entered the Gilao river which bisects the city, and flowed with it into the Ria. V. cholerae was isolated from 9 of 20 water samples taken from the Gilao river May 14–22, 1974.
In the rural area north of Faro, outbreaks of cholera were attributed by the Health Authorities to consumption of water from wells, several of which were culture positive for V. cholerae. The cause of the 59 cholera cases reported in Faro itself in May–September 1974 was unclear, although shellfish were suspect.
In the area around Lisbon, where sewage was sometimes used to irrigate and fertilise vegetable gardens, health authorities initially felt that contaminated raw vegetables, as well as shellfish, might be responsible for most cases ... But
[From Blake et al., 1977b]
... in August, during the peak of the cholera epidemic, Lisbon Health Department noted that some cholera patients reported recent travel to a spa in Lisbon district. At the same time Vibrio cholerae El Tor Inaba was isolated from both the springs which supplied mineral water to the spa and to a commercial water bottling plant. Both the spa and the plant were closed at once ...
The spa had 51718 visitors in 1973, of whom about 20000 came during August. ... Most of the water used by the spa and all of the water for the bottling plant came from spring A, which entered a concrete covered underground reservoir excavated in the limestone from which the spring emerged. Untreated water from this reservoir was piped to the baths, a swimming pool, multiple drinking water sources, and the water bottling plant. A small river carrying sewage from upstream towns ran near the springs. Some of the characteristics of the water from spring A are given in Table 1.1.
At the bottling plant approximately half of the water was carbonated before bottling, and half was bottled without treatment ... There was little change in the amount of this water (Brand 'A') distributed annually from 1969 to 1973 when 10.5 million litres were bottled, but in 1974 production increased by about 50% apparently because many people distrusted public water during the cholera outbreak. In August, the month of greatest demand, bottles moved from the production line directly to waiting trucks and could be on store shelves in Lisbon within four hours after production.
On August 13, after two cases of cholera were reported in residents of a village near the spa, a sanitarian cultured water from springs A and B as part of a sanitation inspection of the area. On August 22 the National Public Health Laboratory reported that V. cholerae had been isolated from water samples from both springs. The springs and the bottling plant were ordered closed on August 23, and the bottled water recalled. A press release on August 24 warned the public that consumption of brand A mineral water could be dangerous. V. cholerae was isolated from five or six water samples taken from spring A on August 13, 22, 26, and 28, and from two of six water samples collected from spring B on those dates; subsequent cultures were negative. Bottled water was not cultured for vibrios. Cultures of three of five water samples collected on August 13 and 26 from the river were also positive for V. cholerae ...
1.1.2 The Investigation in Tavira and Faro, Southern Portugal
[From Blake et al., 1977a]:
Tavira
In Tavira, an attempt was made in October 1974 to locate the 15 cholera patients whose cases were reported during the first four weeks of the outbreak and to question them about their basic demographic data, travel histories, frequency of consuming a variety of foods (including raw fruits and vegetables and seven types of shellfish), methods of cooking shellfish, and sources of drinking water ...
Fourteen of the first 15 cholera patients were located; although their homes were scattered throughout the town, a matched pair analysis implicated water from one spring, the Fonte do Bispo, as the probable source of cholera in 11 cases (p =0.001). The epidemic curve dropped sharply after the spring was closed on May 10. The other spring was not implicated. Although three patients had eaten raw or semi-cooked cockles in April or May, there was no statistically significant association between eating cockles and illness. The first cholera patient was a truck driver who three days before the onset of his illness ate cockles which he had gathered from the Ria de Faro near the mouth of the Gilao river. The cockles were heated until they opened and eaten immediately by three persons. The patient, who took antacids regularly, was the only one of the three who developed diarrhoea. He had not been out of Portugal during 1974.
Faro
In Faro, the 59 patients who had V. cholerae isolated from their stools between the beginning of the epidemic in May and the end of September were studied ... 53 (90%) of the 59 patients were interviewed and matched [with case controls]. Two different exposures, consumption of Brand A commercially bottled mineral water and of raw or semi-cooked cockles were significantly associated with cholera in the initial analysis ...
Sources of water other than bottled water (public water supplies, cisterns, wells, and springs) were not significantly associated with cholera ...
1.1.3 Investigation of the Bottled Water
[From Blake et al., 1977b]:
During August 1974 the attack rate for the 14 000 visitors to the spa from the other counties in Lisbon District was 2.57:1000 (36:14 000) while for residents of those counties who did not visit the spa it was only 0.25:1000 (382:1 530831) ... the relative risk for visitors to non-visitors was 10.3 ...
To determine if Brand A bottled water had caused cases of cholera, a case-control study was performed in the city of Lisbon which showed that the risk for those who consumed the non-carbonated bottled water, rather than carbonated water, was 12. Consumption of carbonated brand A bottled water was not found to be associated with cholera.
1.1.4 The Case Study Source Materials
Blake, P.A., Rosenberg, M.L., Bandeira Costa, J., Ferreira, P.S., Guimaraes, C.L. and Gangarosa, E.J., (1977a), Cholera in Portugal, 1974.I. Modes of transmission, American Journal of Epidemiology, 105 (4), 337–343.
Blake, P.A., Rosenberg, M.L., Florencia, J., Bandeira Costa, J., Prado Quintino, L. and Gangarosa, E.J., (1977b), Cholera in Portugal, 1974. II. Transmission by bottled mineral water, American Journal of Epidemiology, 105 (4), 344–348.
1.2 BACKGROUND
1.2.1 Potable Water
In March 2002 the world population stood at 6.2 billion (6.2 x 109) people, all needing safe potable (drinking) water (www.world-gazetter.com/home/htm). Gastroenteritis and waterborne diseases constantly threaten the lives of children, the weak, the poor and the elderly, and rank high among the causes of mortality.
Human and animal faeces are the primary sources of the incriminated organisms, so secure separation of sewage and night soil from clean and treated water supplies is required. However, implementing the necessary actions takes commitment, time, and investment of huge sums of money. Many societies do not have safe water because, for political and economic reasons, those investments have not been made. Sometimes it takes a serious outbreak of waterborne disease to jolt the relevant authorities into action, until which many peoples in the poorer countries of the world, ill equipped to make investment in infrastructure, continue to suffer endemic waterborne disease.
Drinking water can be supplied variously from the mains, wells, boreholes and springs for use in homes, hotels, restaurants, canteens, cafes and factories. There it is used for drinking, cooking, for hand and body washing, and other tasks, while in food businesses it may not only become part of the foods but is also used for cleaning and rinsing the food processing equipment. Contaminated, it puts the health of users directly at risk. Polluted water used in aquaculture and in irrigation, particularly in horticulture, may contaminate the fruit, vegetables and shellfish, products often eaten without cooking.
In 1987 Galbraith and his colleagues published a review (Galbraith et al., 1987) of the outbreaks of disease transmitted through water in the UK in the fifty year period from 1937. Table 1.2 summarises the incidence of waterborne disease in the UK in the years 1937 to 1986, and Table 1.3 breaks those statistics down indicating the types of water sources and the probable causes of contamination. In 1937, Croydon, to the south of London, suffered a waterborne outbreak of typhoid fever infecting 341 people of whom at least 43 died. It was a turning point. Following that outbreak, national surveillance of water quality was stepped up while increased attention was paid to the effectiveness of purification and chlorination procedures, as well as to maintenance of the integrity of water supply systems.
Galbraith and his colleagues demonstrated that the principal causative bacteria of waterborne disease in the UK in that half century were Salmonella typhi (typhoid), Salmonella paratyphi B (paratyphoid), Campylobacters (gastroenteritis), Shigella sonnei and other Shigella strains (bacillary dysentery). Additionally other organisms, amoebae such as Entamoeba histolytica (amoebic dysentery), Cryptosporidia (cryptosporidiosis), Giardia lamblia (giardiasis) and viruses (gastroenteritis) caused a significant number of cases of illness of varying degrees of severity both directly through infecting water, and indirectly through water contaminating food (see Table 1.4).
Although some outbreaks were associated with untreated water supplies, other water supplies, although chlorinated, were polluted by inward leakage of sewage and became unsafe. Note that other agents such as hepatitis, polio and Norwalk viruses, other salmonellae and E. coli, also associated with sewage and excreta from birds and animals, also cause waterborne illness.
1.2.2 Bottled Water
The origins of bottled water probably arise from the drinking of spa water for health reasons followed by taking a few bottles away after the visit to prolong the perceived health giving effects of the mineral water. In the UK sales of bottled water have been rising rapidly. It was estimated, for example, that the volume of cooled bottled waters sold in the UK was approximately 195 million litres in 1999, predicted to increase to 333 million litres by 2003 (Bottled Water Coolers Association, 2002).
Contrary to many people's expectation bottled water is neither sterile, nor incapable of supporting the growth of a microbial population. A review by Hunter (Hunter, 1993) shows that the microbial population (the TVC, 'total' viable count) of both still and carbonated water at the point of retail sale can range between < 102 and as high as 104 organisms per millilitre, while the range for still water can be wider, sometimes reaching as much as > 106 ml-1.
That population can be very mixed and, because of concerns that pathogens could be among that flora, several workers have looked for specific types of organisms. Table 1.5 shows the variety both in types of organisms and numbers of samples of water in which they were present.
Many factors associated with the water – its source, how it is produced, and its chemical composition and pH, combine together to affect the numbers and types of organisms present. Later in the time period in which the bottled water is distributed and sold other factors influence whether the population dies out or increases. The major concern is of course whether the population of organisms it contains represent a health risk. Table 1.6 summarises some of the factors influencing the microbiology of bottled water.
(Continues...)
Excerpted from Case Studies in Food Microbiology for Food Safety and Quality by Rosa K. Pawsey. Copyright © 2002 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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