Investigation of Food Poisoning Outbreak

Investigation of Food Poisoning OutbreakChristian NehmeINTRODUCTIONAn probe of a nourishment poisoning outbreak requires some knowledge into what solid aliment poisoning is and some special K culprit bacteria which trigger such outbreaks. Food poisoning, too known as alimentborne unwellness, is the name for the pad of illnesses caused by finishing or drinking contaminated fare or drink. Food poisoning occurs in two principal(prenominal) ways poisoning by toxic agent or by infective agent. Food intoxication is when the food contains toxins, usu tout ensembley occurring when the organism that produced the toxin is no longer present or open to cause infection. Food infection, on the separate hand, is when the food contains bacteria which infect the body afterward it is eaten. Foodborne illness is quite common, affecting almost 5.5 million Australians each year.Two common food poisoning create bacteria atomic number 18 B.cereus vs S. aureus. barn species are Gram despoti c, aerobic heterotrophs, with the ability to form resistant spore coats.Do they deliver similar symptoms, toxins?cases in Australia.Description of ScenarioAs a special treat paid for by the Department of health and Aging, 435 pensioners were taken on a catered summers day harbour cruise. posterior that day, a way out of the participants became very ill.The food was prepared on shore and brought onto the boat that day, The boat go away aviator Quay at around 10am and cruised around Sydney Harbour past Watsons Bay, into Darling Harbour and disembarking at Circular Quay at 3pm.. The water was rather calm and there was a medium breeze.Local hospitals and ambulances were mobilized to respond to the outbreak. It likewise came to the attention of the local PHU and their personnel were able to retrieve some remnant food and patient specimens from the stab and hospitals.Questionnaires were distributed to the guest list once this was obtained by the local PHU and the NSW Food Authorit y. Of the questionnaires sent out, 339 were returned providing the following information.SymptomsOf the total number who were sick, 153 suffered severe diarrhoea 139 stinkered 122 experienced abdominal cramps 117 said that they felt nauseous 11 complained of numbness in the arms and legs and 3 developed haematuria. Thankfully no deaths were recorded as a consequence of this outbreak. inform details on illness, and what was eaten and non eaten were compiled into Food Attack Tables.RESULTS matter of individuals who attended the cruise435Number of questionnaires returned339Number of individuals who suffered diarrhea 153Number of individuals who suffered vomiting 139Number of individuals who suffered abdominal cramps 122Number of individuals who suffered nausea 117Number of individuals who suffered numbness in arms / legs 139Number of individuals who suffered haematuria 139Number of deaths 0The incubation arrests of the sick individuals (number of cases) are displayed in framing 1. The food- circumstantial attack arranges for foods thought to be implicated are shown in Table 1.Figure 1 Epidemic curve presenting incubation periods of sick pensioners aboard the harbour cruise. Results obtained from responses to a questionnaire. Onset measure turn out as two distinct peaks, one occurring between 2-3 hours and the other between 6-15 hours, after consuming lunch. info CalculatedPercentage morbidity (219 x 100) / 339 = 64.6%Percentage mortality (0 x 100) / 339= 0.0%Percentage case extremity rate (0 x 100) / 219= 0.0%Average incubation period = 9.9 HoursTable 1 Food-specific Attack rates use data from questionnaire and other calculations including the odds Ratio, Chi squared and Confidence legal separation for each food fount.Odds Ratio An odds ratio great than 1 indicates a higher run a risk of becoming risk on eating that particular food type. In Table 1 above, all meats have an odds ratio less than 1, and only sift pud with Custard has an odds ratio gr eater than 1.Confidence Interval the Odds Ratio is within a 95% trustfulness level if the CI does non let in 1. From Table 1, junction Lamb is the only food not within a 95% corporate trust level, whilst the 3 other food types are within a 95% confidence level.Chi-SquaredHo = the unhealthiness is not a result of any of the food consumedH1 = the indisposition is a result of any of the food consumedWhen the P-Value is less than 0.05 (non-signifi groundworkt), the null venture evict be rejected. Since the P-Value is less than 0.05 for the Chicken, Ham sieve pud, the null hypothesis can be rejected, indicating that the case of the sickness was due to the consumption of either one of, or a combination of these foods. Since the P-Value of the guy Lamb is oft greater than 0.05, the null hypothesis cannot be rejected, signifying that the consumption of the Roast Lamb was most probably not a cause of the sickness.% Ill (Attack Rate) this is a measurement of correlation of the pe rcentage of passengers who got sick and the total number who ate or did not eat a specific type of food. The correlation for Rice pud was the one to stand out, where only 20% of the passengers who did not eat rice pudding actually reported that they got sick. This is dramatically less than the other food types, which were above 60% each. Also, Rice Pudding had the highest attack rate of 57.8%.Flowchart of Experiment Food Swabs Cooks wind up Swab Faecal SwabResults of ExperimentDISCUSSIONAs evident from Figure 1, the number of cases are spread out from 2-21 hours after consuming lunch. There are 2 distinct peaks, occurring at 2-3 and 6-15 hours after consuming lunch. At this stage, a pathogen can possibly be the causative agent as it has shown to present such symptoms on passing from the Upper Gastrointestinal tract (GIT) to the Lower GIT(Kho et al. 2011). These peaks can be cogitate with vomiting and diarrhoea, respectively. Of the commonly known pathogens, Bacillus cereus, a spo re-forming pathogen, causes two distinct forms of foodborne nucleuss an emetic syndrome (vomiting-typified by an incubation period of 16 hours) and a diarrheal illness typified by an incubation period of 624 hours (Benenson AS, ed).Table 1 yields useful results which play a critical role in identifying the trigger organism for the outbreak. The attack rate for people who ate the different food types was the highest for Rice Pudding Custard (57.8%), although the other food types were closely behind, Roast Lamb be the closest at 56%. This is not bounteous information to be able to conclude the causative food type since the attack rate only ranges by 7%. This close range could be due to the fact that these food types were consumed in varying combinations, which makes it difficult to pinpoint the exact, single food at fault. This attack rate, however, can be have with the attack rate of the pensioners who did not eat a particular food type, giving a clearer compute as to what the causative food source was. Rice Pudding Custard, having the lowest attack rate at just 20%, suggests that if it were not eaten, the chance of becoming ill is heavily less compared to the nearest food type, Roast Lamb, with an attack rate of 62.2%. This, combined with the high attack rate of pensioners who ate the Rice Pudding Custard, signals it to be the culprit source of pathogens.The odds ratio of Rice Pudding Custard, being 5.47, is significantly greater than other food types (which are all less than 1), suggesting that the risk of becoming ill upon consumption is 5.47 times greater than if Rice Pudding werent consumed. Furthermore, since the P-Value is less than 0.05 for the Chicken, Ham Rice Pudding, the null hypothesis can be rejected (that the sickness is not a result of any of the food consumed). This indicates that the case of the sickness was due to the consumption of either one of, or a combination of these foods. Since the P-Value of the Roast Lamb is much greater t han 0.05, the null hypothesis cannot be rejected, signifying that the consumption of the Roast Lamb was most probably not a cause of the outbreak. However, the Confidence Interval for Rice Pudding Custard lies within a 95% confidence level, except supporting the claim that the Rice Pudding Custard was the causative food source.Knowing the possible food source which triggered the outbreak, and having an idea that the causative organism behind the outbreak was B. cereus (due to the two peaks correlating to the typical symptoms), research laboratory investigations were then conducted to conclude what the exact organism was. The first test conducted was inoculating each food seek onto a PEMBA plate. The results varied as to the PEMBA count (cfu/g), possibly due to experimental error. However, Rice Pudding had the highest self-consistent overall count, with 8.5 x106 and 7.9 x 106 cfu/g. The colonies that grew on the PEMBA plates for the Chicken, Ham and Roast Lamb were small, yellow colonies, measuring approximately 1-2mm each, indicating the adventure of Gram Positive Cocci. The Rice Pudding, however, displayed large (4-5mm), matt blue colonies with a halo of precipitate. The PEMBA isolate for the Rice Pudding were Gram Positive Rods, occurring in chains with an oval central spore. The lipid granule test was positive and catalase positive, with motile cells. Since none of the other food types PEMBA isolates showed GPR, no further testing was conducted on Chicken, Ham and Roast Lamb.Salmonella, Enterococcus and Shigella may have been possible pathogenic causing bacteria which contributed to the outbreak. In order to overstep or support this possibility, a Xylose Lysine Deoxycholate (XLD) plate was used. Faecal swabs of the sick pensioners who had eaten a particular food type were inoculated onto the XLD media. The only differentiating outcome was the appearance of the colonies of the faecal sample from people who consumed the Rice Pudding Custard, were sli ghtly big than those for the other food types. No definitive conclusion can be made from this. Faecal swabs were overly plated on PEMBA plates and inoculated into the XLD media. The PEMBA plates displayed small, yellow Gram Positive Cocci colonies for the Chicken, Ham Roast Lamb specimens. The Rice Pudding Custard however, displayed large, Gram Positive Rods, which appeared as large, blue, matte colonies when sub-cultured onto the PEMBA plates. This further supports the finding that B.cereus was the causative organism.The next step is to eliminate any possibility that the pathogen Staphylococci spp had any part to play, or to confirm that it did. To do this, the Cooks nose swab was inoculated on Blood nutrient nutrient agar (BA) to stablish haemolysis and on Mannitol Salt Agar (MSA), as a selective mechanism for salt-tolerant microorganisms such as Staphylococcus or Enterococcus. After testing, small, round, flat, hemolytic white colonies were seen on the Blood Agar, with the BA Isolate being Gram Positive Cocci, occurring in clusters and being catalase positive. Although this suggests the possible carriage of a Staphylococci species, the MSA plate rendered small, white colonies with pink agar throughout. The pink agar confirms that the Mannitol was not fermented, which is an indicator that no Staphylococci species was present. Further proof for the non-existence of S.aureus was seen with the Latex test displaying no clumping.In order to confirm that B.cereus was the causative organism for the outbreak, further tests were conducted. These include gelatin positive, starch positive, casein negative, nitrate positive (no gas formed). The sample tested positive for Glucose VP. This means that glucose was broken down by the Rice Pudding specimen to form acetoin, and was evident through the dark red colour formed. B.cereus tested negative for the indole test, meaning it was unable to split indole from tryptophan (Wong, Chang Fan 1988). All these test result s correspond with the presence of B. cereus and at this point, we are more confident that this is the causative organism. To test for purity, and to confirm that no other specimen influenced these results, a BHIA purity test was performed, which resulted with a pure result, meaning the listed test results were solely caused by the Rice Pudding Custard specimen.Through the results of the media growth and the results of the confirmatory tests conducted, it was determined that the causative food source was the Rice Pudding Custard, which contained a strain of B.cereus. This resulted through the Cook not cooking the Rice at the warning temperature, and since the temperature used was hot enough to trigger the B.cereus to enter their vegetative state, but was not high enough to kill the B.cereus, this resulted in the widespread growth of the specimen. Accompanied with the fact that the rice was prepared the night onward and the warmer environment in which the rice was kept for the per iod of time overnight were suitable conditions and promoted its growth, further accounts for the growth of B.cereus (Jesen et al. 2003).Outbreaks such as this could be avoided, and at least minimised if some precautions were taken by all those involved with the handling, making and consuming of foods. The following list outlines some main ways through which this can be achieved (Klietmann, W, 2002)Storage of hot food above 600C and cold food in the fridge down the stairs 40CKeeping cooked and raw(a) food separated at all times, to avoid cross-contaminationUsing separate chopping boards and utensils for raw and cooked foodsImproving hygienics such as washing hands before and after contact with foodUtilising a heat process to destroy the vegetative cells and a rapid cooling process to stop the spores from germinatingUsing appropriate cleaning and disinfection of contact surfaces of food, such as sodium hypochlorite based disinfectantsKeep frigid foods frozen until usedCooked foods which wont be consumed within an hour should be kept at temperatures below 10C or above 50C (Roberts, T.A)Experimental MethodThe main source of primary data was obtained from the questionaries. The accuracy of the answers to the questions asked has a direct influence on the results obtained, and on the findings extracted from the questionaries. Thus, if the questionnaires are completed truely and in detail, the reliability of the results would increase and a higher potential in obtaining accurate leads as to which species were the triggers to the outbreak would be attained. However, out of the 435 pensioners who were on the cruise, only 339 questionnaires were completed and returned to the local PHU the NSW Food Authority. This leaves 96 unaccounted for pensioners, which would have aided and fastened the search for the possible trigger. These 96 absences could have been a result of the pensioners not wanting to give out personal information, not having an easy method of returning the questionnaires, and some pensioners may not have received the questionaries in the first place. This absence of 96 responses has a direct effect on the accuracy of the collected data from these questionnaires, as the data is only a sample of the population, and is not a complete reflection of all pensioners involved. Furthermore, more detailed questions could have been asked on the questionnaires which may have sped the process of identifying the relationship between the symptoms caused and the time of onset.Improvements with the data collection could have involved the collection of vomit and diarrhoea samples, which would have helped identify the pathogen early on in the investigation. API strips could have been used to aid in identifying the pathogen as fast as possible, as well as using advanced technological methods. test the venue of where the food was prepared further and analysing all possible contributions to the outbreak at the source by further investigating the cook, the staff involved, whether other foods were being prepared at the same time, the overall hygienics of the kitchen, pest related influences, and previous occurrences and whether any have occurred since. Continuous monitoring of all food zeal methods and staff involved since the occurrence will aid in preventing a reoccurrence. A stricter enforcement of an increased hygiene standard could be rolled out onto not only similar cruise companies, but also all kitchens and restaurants throughout Australia. The most feasible and economical method would be to allocate fortnightly swabs of the kitchen, staff, floors, equipment and food samples at all these food-related location, and be sent to relevant laboratories to be analysed and reported. A safety-tick program could be enforced which takes these results and businesses can display them, notifying customers that they conduct regular hygiene tests and have passed all tests, giving the customer append of mind that their chances of gettin g food poisoning is less likely.REFERENCESJenson, I Moir, C. J In Foodborne Micro-organisms of Public Health Significance. A. D. Hocking et al. (editor) 6th edition. AIFST (NSW Branch) Waterloo NSW 2003.SAA Australian Standard. Food Microbiology. Method 2.6 Examination for specific organisms AS 1766.2.6, pp. D8-D12, 1991.Benenson AS, ed. Control of communicable diseases in man. 15th ed. Washington, DC AmericanPublic Health Association, 19901778.Kho, M.F., Bellier, A., Balasubramani, V., Hu, Y., Hsu, W., Nielsen-LeRoux, C., McGillivray, S.M., Nizet, V. Aroian, R.V. 2011, The pore-forming protein Cry5B elicits the pathogenicity of Bacillus sp. against Caenorhabditis elegans, PLoS One, vol. 6, no. 12, p. e29122.Wong, H., Chang, M. Fan, J. 1988, Incidence and characterization of Bacillus cereus isolates contaminating dairy products, Applied and environmental microbiology, vol. 54, pp. 699-702.Jesen, G.B., Hansen, B.M., Eilenberg, J. Mahillon, J. 2003, The hidden lifestyles of Bacil lus ceresus and relatives, Environmental microbiology, vol. 5, pp. 631-40.Roberts, T. A. Baird-Parker, A. C. Tompkin, R. B. (1996). Characteristics of microbial pathogens. capital of the United Kingdom Blackie Academic Professional. p.24.Klietmann, W. and Ruoff, K. 2002. Bioterrorism Implications for the Clinical Microbiologist. Amer. Soc. Micro. 14(2)364-381.