Foodborne Illnesses: Causes and Impact

Introduction

Food borne diseases affect millions of people each year. From a mild reaction such as diarrhoea, vomiting, abdominal cramps to severe problems such as haematuria, long lasting health problems and possible death (9). The most common bacteria that are responsible for foodborne illnesses are: Staphylococcus aureus, Salmonella, Norovirus, Shigella Campylobacter, and Clostridium perfringens. These organisms can be found in different habitats such as in water, soil, on the skin and inside the nostrils of humans as well as on raw meat or poultry(10). It is a serious disease for which people are suffering a lot from severe pain or other chronic symptoms in the human body. It is hereby, necessary to conduct in depth research so that it is possible to identify the contaminated food for which the people suffer a lot. Foodborne pathogens propagate due to various factors and these factors consist of lack of hygiene, undercooked/raw food, and unpasteurised fruits juices. Foodborne pathogens cause illness by contaminating food without changing its smell, appearance or taste.Thus, it is difficult to determine whether the food is safe to consume or not (4). People are likely to be susceptible to foodborne diseases including pregnant women, young children, older adults, and people with weak immune systems due to various medical conditions or old age (5). In the following experiment, a foodborne outbreak had occurred in which university students and their grandparents got ill. It was a warm summer morning, and they were heading to Taronga zoo for a day’s outing. For lunch they took cut sandwiches and cartons of rice pudding prepared at the university canteen. Before arriving at the zoo, many had started eating their sandwiches. Members of the group started getting sick before arriving at the zoo. As they arrived at the zoo several people were sick by then and they were admittedto the local hospitals. A case study was conducted thereafter which included taking remnants of food and stool specimens from those taken to the hospital. There were two reasons why this outbreak occurred. The first that the cook handled the food without wearing gloves with infected handsand the second that the refrigerator motor failed so that conditions were warm inside the cabinet conditions were ideal for multiplication- warm summer weather and lack of refrigeration. In order to find out the causative organism, biochemical tests such as oxidase, catalase, gram stain and latex coagulase tests were taken. Thesamples of chicken, ham, rice pudding with custard and roast lamb were plated on agar plates. Food specimens were plated on Baird Parker agar plates, faecal specimens were plated on Mannitol Salt agar and MacConkey agar plates. Swabs were also taken from the pus of cook’s thumb, the nose of the cook and his assistant and plated on MSAand HORSE BLOOD AGAR PLATES.

Aim

The aim of the study is to determine the cause of the organism that is responsible for contaminate food which has resulted illness as well as the study helps to discover how these organisms got in contact with the food, spread and multiplied.

MethodsAs illustrated in Epidemiology and public health microbiology lab manual

Results

The questionnaires were distributed among the people who were involved in the outbreak for such contaminate food and there were 221 respondents who returned the questionnaires with proper feedback and information. The recorded data was obtained from groups that were separated according to the type of sample given to them.

The odds ratio, of all the food types: Chicken, rice pudding with custard, ham and beef are shown respectively. As per the above table, it has been seen that, there is high presence of Ham which raises organism among the people for consuming high quantity of ham. (Rere to Appendix 1) Continue your exploration of Foodborne Illnesses: Causes and Impact with our related content.

The table above shows the food-specific attack rates of all the food types, from the persons eating food and not eating food and the ill percentages are given for each food type. From the people that ate food, the highest ill percent rate was for ham (59.2%) and from the persons not eating ham had the least ill percentage (25%). (refer to Appendix 2)

Figure1 shows the number of cases onset after eating lunch. The major illnesses occurred between 0.5-6 hours as it can be seen from the graph.

The food samples that are shaded grey in table 3; which indicates that, Chicken, beef, and rice pudding with custard had no growth of colonies on the BPA plate, therefore no further tests were conducted. However, ham grew in BPA plateand its colony morphology was 3 millimetres with black colonies, a zone of cloudiness and halo of clearing respectively. The colony-forming unit(CFU) for ham was 2.5 x 107(CFU/g) for the first group that conducted the experiment and 4.6x107 (CFU/g)for the second group. The cell morphology of ham was gram positive cocci (GPC) in clusters. Additionally,biochemical tests were done to further assist in the identification of the pathogen such as the, catalase test which had a positive result. There were some suspicious colonies,itwas latex coagulase and Dnase positive. The analytical profile index (API) id is 6736153.

Chicken, beef and rice pudding with custard had no growth. On the other hand, Ham had growth on both Mannitol agar plate(MSA) and MacConkey (MAC) agar plate. In MSA, the colony morphology for ham was less than 1 millimetre, circular and yellow, which means it is a mannitol fermenter. The cellular morphology was GPC in clusters. The catalase test was positive. There were suspicious colonies. However, in MAC, ham had 2 different organisms grown on it, therefore it had 2 different results. The first columnincluded 1 mm circular pink colonies, with GPC in chains and negative for catalase test and there were no suspicious colonies. The second had 2-3-millimetre circular pink colonies, with gram negative rod (GNR) singular, and a catalase test negative and with no suspicious colonies.

Table 5 represents the results for cook’s nose on HBA and MSA. The results for all were the same on HBA. Although on MSA they were different.For the cook’s nose on MSA the colony morphology was less than 1 millimetre, circular, with yellow colonies (+ve mannitol). The cellular morphology included GPC in clusters, with a positive catalase test, latex coagulase test as well as DNase test. API STAPH ID is 6736153.S.aureus was sensitive to all antibiotics. (Refer to ppendix 3)

In table 6, all the antibiotics, that were used in this experiment, represented. S.aureus is sensitive to all the antibiotics. However, as shown in the results Vancomycin appears to have a diameter below 15 millimetres which shows S.aureus is not sensitive to it, however it is but this was an incorrect result due to vancomycin being a large disc that diffused into the agar plate very slowly.

The questionnaires

The biochemical tests are beneficialfor the presence of certain enzymes that also determines which nutrition and which isolate can or can’t use and determines oxygen requirements. The number of pensioners which were ill was 200 and 3 of them died. Their percentage morbidity was 90.6% and mortality was 1.3%, with a percentage case fatality rate of 1.5%. The incubation period was 3.04 hours as shown in figure 1. The cooks family got sick the latest because they received the food the latest

Discussion

The discussion section is developed to reach decision regarding the actual reason behind occurrence of the food poisoning among the individuals by analysing the results and information developed. The typical method for tracing bacteria used in this experimental study was done to identify if the foods were contaminated by S.aureus. The Strain typing is used to detect single strains of bacteria to show substantially that the isolates are indistinguishable and therefore may be related in the outbreak because S.aureus is found very commonly in the environment. (8) The other identification methods of S.aureus include in this study was Serological detection, typing of enterotoxins, phage-typed, DNA(RFLP AND PFGE) and multi-locus sequencing typing (MLST). The purpose of the DST (drug sensitivity test antibiogram) in this outbreak was an attempt to show that the isolates are indistinguishable. (Refer to Appendix 4)

Table 1

In table 1 the odds ratio, in the context of all foods is the measurement of the likeliness of an outbreak to occur from different types of mediums (food type’s e.g. Chicken, Ham, beef and rice pudding). Based on these values we can determine the significance and relevance to the clinical case study (food outbreaks). The Odd values were calculated for the types of foods in the table above and this clinical case informs that Ham had the highest value which is 4.46 which shows a significant value greater than 1.0. The value greater than 1.0 odd ratio informs that the exposure might have been the key risk factor for the development of the disease (13). Thus, Ham was contaminated by the cook and it was the vehicle of spread for pathogen as the odd ratio of all the food types showed that the ratio is greater than 1.0 in Ham and in no other food types. Thus, it can be decided that the bacteria spread among the individuals through the eating of the Ham.

Table 2

Table 2 shows the food-specific attack rates of all the food types from the persons that ate the food while going to the zoo. In the results, it can be seen that ham had the highest ill percentage (59.2%) because it was contaminated with bacteria which produced toxins. Thus, Ham acted as the key risk factor for development of food poisoning can be decided from Table 2 as the percentage difference of food-specific attacks were also found to be more with people who ate Ham in comparison to the ones who did not eat Ham. However, the other people who have not eaten the food may have got sick due to the unhealthy environment where most of the individuals were vomiting. Moreover, they could have also got sick through the transmission of the bacteria by coughing or sneezing or any other physical contact with the people who were infected by the bacteria while eating the food.

Figure 1:

In figure 1 the major illnesses occurred was between 0.5-6 hours. S.aureus is a gram-positive bacterium and is carried by 30% of the participants either in their nose or skin (6). It is informed that toxins of S.aureus at 1-6 hours incubation period are called enterotoxins. Since the results in figure 1 informed that most of the individuals consumed the food within 6 hours of their preparation thus it can be identified that the food poisoning was spread among the people due to the release of the toxin by the bacteria rather than itself.

Table 3

In table 3, chicken, beef, and rice pudding with custard had no growth of colonies on the BPA plate because they were not contaminated and did not contain the organism responsible. This shows that they had no interference in the outbreak but ham had growth in BPA plate which referred it to be contaminated. Biochemical tests were done to further assist in the identification of the pathogen such as the catalase test, which is a test that distinguishes bacteria that are able to produce catalyse enzyme. The only staphylococcus can produce catalyse enzyme and because the test showed catalase positive, it was confirmed that it was S.aureus. There were some suspicious colonies due to the presence of causative pathogen S.aureus. It was latex coagulase positive, which is the test done to identify S.aureus and DNAase positive that is a test that distinguishes microorganism based on their DNase activity. The API gave a percentage of 97.7% correspondence to S.aureus.

Table 4

The Chicken, beef and rice pudding with custard had no growth and Ham had 3 colony morphologies because it included 3 different organisms. On the other hand, Ham had growth on both Mannitol agar plate (MSA) and (MAC) agar plate. In MSA, the colony morphology for ham was less than 1 millimetre, circular and yellow, which means it is a mannitol fermenter. Most pathogens are mannitol fermenters and this indicates that it is most likely Staphylococcus. The cellular morphology was GPC in clusters. The catalase test was positive and there were suspicious colonies. All of this indicates that the organism present was S.aureus. However, in MAC, ham had 2 different results where the first column of results included 1 mm circular pink colonies with GPC in chains and negative for catalase test and there were no suspicious colonies. These results indicate that it was a non-pathogenic bacteria called Enterococci. The second column had 2-3 millimetre circular pink colonies with gram-negative rod (GNR) singular and a catalase test negative and with no suspicious colonies. This also indicates that it was a non-pathogenic bacteria, however, E.coli was the organism this time. The API for ham gave a percentage of 97.7% which corresponds to S.aureus.

Table 5

On the HBA plate, the cook’s nose and the cook’s assistant nose and Pus from the cook’s thumb had the same results for day 1. However, On MSA plate cook’s nose results correspond to the results of the pus from cook’s thumb. This is because they both had the same organism involved which was S.aureus. The reasons are the presence of suspicious colonies and another reason is that they were both mannitol fermenters. The analytical profile index (API) id which is used to identify bacteria gave a best and faster way to identify the bacteria. It gave a percentage of 97.7% correspondence to S.aureus. (11) It was latex coagulase positive, DNase positive which also helped in the identification of S.aureus. However, for the cook's assistant nose, the organism involved was S.epidermis which was different from the rest. This was due to the results being different. The bacteria wasn't a mannitol fermenter and didn't change colour from pink/red to yellow, there weren't any suspicious colonies present. It was also coagulase and DNase negative. And the API gave a percentage of 97.8% correspondence to S.epidemis.

Table 6

In table 6 all the antibiotics that were used in this experiment represented S.aureus which found to be sensitive to all antibiotics. However, as shown in the results Vancomycin appears to have a diameter below 15 millimetres which shows S.aureus is not sensitive to it. Thus, it can be determined that the given antibiotics except Vancomycin can be administered to the patients for treatment purpose to resolve their health issues. This is because in all other antibiotics they showed antibiotic sensitivity meaning the bacteria cannot grow if the following antibiotics are administered.

Conclusion

Thus, from the collected information it can be concluded that the key causative agent for food poisoning among the individual was S.aureus. The people were affected by eatingHam as it showed the most extent of odd ration from other ood types. Moreover, the infection came from the infectious hands and nose of the cook as the person was not covering their mouth or hands while preparation of food. Therefore, lack of hygiene among the cook became the main concern in this respect that caused relapse of the food poisoning among the individuals.