Case-Control Study Of Cryptosporidiosis Outbreak In UK Petting Farm

Study Design

Describe about the Cases-Control Research for UK based Petting.

The cases-control research is about research carried out to investigate outbreak of cryptosporidiosis in visitors of an England petting farm caused by a subtype Cryptosporidium parvum. The study is about infection and epidemiology of Cryptosporidium parvum subtype. Cases were those with cryptosporidiosis while controls were those without the infection. The following is critical appraisal of the case-control study of cryptosporidiosis outbreak in England cased by Cryptosporidium parvum subtype.

The purpose of the research is to retrospectively analyse the exposure to risk that caused cryptosporidiosis disease outbreak in visitors to a petting farm. The study comparability identifies the relationship between exposure to risk factors and outcome factors (Rose and Mark, 2008). The study design is case-control study design. The study retrospectively compares patients with cryptosporidiosis as cases to those without cryptosporidiosis as controls with the focus on the frequency of exposure to the Cryptosporidium parvum risk. This is an appropriate design for the study. The case control research gives comparison between the controls and cases and relationship is established between risk factor in the study and cryptosporidiosis disease as outcome. In the research, outbreak of cryptosporidiosis is compared based on its causal attribute. Case control study is used to study causal factors of disease outbreak starting with outcome to exposure to risk factor (Chalmersand Giles 2010).

In the study, visitors to petting farm were used as subject to recruit cases and controls through snowball sampling techniques. 38 cases out of the reported 46 cases were used in the study and compared to 39 controls that had no cryptosporidiosis infection. The target population in the study are visitors to a petting farm in United Kingdom. The study focus to examine the infection of cryptosporidiosis in visitors that came to farm located in England industry-compliant petting farm caused by Cryptosporidium parvum subtype. The sample is representative of the target population. Firstly, sampling techniques use recruited the sample in a way that is easy to minimize sampling errors. Secondly, the study requires recruitment of cases and control from study subjects. Therefore, the cases and control are used to represent the target population.  Thirdly, sample which consists of 38 cases and 39 controls clearly shows that cases were good representation of the 46 cases of outbreak reported in the study (Toth and Hauser et al 2008).

Study factors are washing of hands, verbal communication of risk and presence of Cryptosporidium parvum. Secondly, washing of hand before eating in the study is a risk factor that determines the level of exposure of the cases and control to Cryptosporidium parvum. Secondly, verbal communication of infection to visitors in the open farm is another factor that determines the exposure to Cryptosporidium parvum. In the study, the number of those visitors with diseases is 10 times less likely to have been cautioned of the cryptosporidiosis risk. Finally, Cryptosporidium parvum is also a risk factor in the study. Cryptosporidium parvum is indicated in the sample as factor that leads to the cryptosporidiosis disease outbreak. Study factors were obtained through interview of cases and controls that were recruitment by use of snowball sampling method (Gargala 2008).

Study Factors

Outcome factors in the study are cryptosporidiosis outbreak, non-compliance with hand washing hygiene, lack of verbal communication of infection risk and infection of farm animals. Cryptosporidiosis outbreak is one of the outcome factors that were investigated in the study. Secondly, non compliance with the hand washing hygiene is one of the outcome factors in the study that determines cryptosporidiosis outbreak as outcome of the study. Thirdly, it was also identified that lack of verbal communication of infection of cryptosporidiosis to visitors. The researcher state that disease outcome are 10 times less likely to state of being verbally cautioned of risk of cryptosporidiosis disease on arrival at odds ratio 0·10, 95% CI 0·01–0·71, P = 0·02. The information was obtained through analysis of data and sample from the field that are from interview. The data obtained was analysed using multivariable logic regression that gave the result (Leske and Wu, 1996).

Potential confounders in the study are farm animals and pets. According to the conclusion of the researcher explain the identification of Cryptosporidium parvum gp60 subtype (IIaA19G1R1) in the samples from lamb feaces meaning farm animals also had exposure to risk factor. The researcher shows that Cryptosporidium parvum gp60 subtype was present in a sample obtained from lamb wastes and all other disease case. A precautions measure was developed to deal with future zoonotic infections from such animals through effective communication of risk to public and farm visitors.

The potential biases in this study are recall bias, temporal bias and interviewer bias. The retrospective nature of the study makes it easier to bias since cryptosporidiosis outbreak and exposure occurred before the study. Cases and control had to recall past exposure to the disease based on their knowledge on being a case. Temporal bias can potentially occur since the researcher has to link between exposure and outcome without considering that exposure to cryptosporidiosis occurred before diagnosis. Interviewer bias can occur because the researcher normally record information based on their knowledge on cryptosporidiosis.

The effect of recall, temporal and interviewers bias is that it gives rise to non-comparability of cases and control in the study. Recall bias for instance, may lead to misinformation that does not give good result when comparing different risk factors. In addition, recall bias can lead to poor data as the cases can give information limited to their knowledge and memory. On the other hand, interviewer’s bias can affect the overall result since the information link by researcher is theoretical and not practical as expected.

Outcome Factors

Statistical methods such as snowball sampling method, regression analysis and interview were used in the study. Firstly, snowball sampling method was used to recruit cases and controls in the study. Secondly, regression analysis was used to analyse the data. In the study multivariable logical regression analysis was used that resulted in identification of relationship between cases of cryptosporidiosis and control. Thirdly, as case control study, data were collected through interview of the informants.  These statistical methods were appropriate since statistical methods such as regression analysis is used to establish the relationship between outcome and risks factors in the study (Chalmers and Giles 2010).

Strengths of the study include effective in study of disease and exposure studies, the study can be used to investigate multiple exposures to cryptosporidiosis,. Firstly, the study design itself is easy to compare cryptosporidiosis disease and the level of exposure of the farm visitors to the disease. Secondly, multiple exposures to cryptosporidiosis diseases can easily be studied since case control study design allow comparability of different exposure to the outcome of the study. Thirdly, case control study is effective in studying rare disease outbreak as in the case of cryptosporidiosis. Finally, the study provides easy analytical comparison as compared to other study options such as cohort studies (Kenneth and Ray 2004).

Weaknesses of the study include possibility of bias, the sequence between exposure of farm visitors to risk factor and cryptosporidiosis disease is not ease to establish, difficulty in determining of cryptosporidiosis incidence rate in control and cases. Firstly, the study present possibility of multiple biases such as selection bias, observer’s bias, recalls bias and temporal bias. These biases can potentially make comparability of exposure to Cryptosporidium parvum and outcome of the study difficult. Secondly, it is difficult to establish the sequence between the exposure of farm visitors to Cryptosporidium parvum and the cryptosporidiosis disease. Thirdly, the estimation of incidence rates of cryptosporidiosis is not easy when the study is not population based (Ioannidis, 2005).

The main result of study is identification that those with disease were 5·5 times higher than those who without dieses and have eaten without observing hand washing hygiene at 95% confidence interval (CI) 1·51–19·9, P = 0·01]. Equally, cases were 10 times possibly not verbally informed of outbreak of cryptosporidiosis  on arrival to the farm at odds ratio 0·10, P = 0·0295% CI 0·01–0·71.  I think the result is valid because strength of the study outweigh the weaknesses of the study, the result clearly show the relationship between risk factors and outcome and Firstly, the study has successfully compared the relationship between cryptosporidiosis disease and washing of hands as risk exposure as revealed in the result. According to results, cases are 5.5 times likely to depend on hand washing hygiene and 10 times unaware of infection. Secondly, the likelihood of the weaknesses such as biases is minimal and can be minimized through careful planning of data collection and analysis (Greenland and Lash 2008).

Potential Confounders

The author concluded that lack of public communication of cryptosporidiosis and failure to keep hand washing hygiene has significant relationship with exposure to cryptosporidiosis on the petting farms. In addition, authors cite their findings as important in advising petting farm visitors on the public health importance to prevent further outbreak of infections. I agree with the conclusion of these authors since their result indicates that infections identified are 5·5 times higher than those without infection who have eaten without cleaning their hands in the petting farm. In addition, according to the odd ratios of odds ratio 0·10, P = 0·02, 95% CI 0·01–0·71, and mean that there is significant relationship between different study factors of the study (Grimes and Schulz 2005).

Suppose the results of the study were valid the most important public implications of this paper would be cautions when visiting petting farms, personal hygiene will be emphasised before eating and farm animals would be highly examine for zoonotic infections. Firstly, public will be more cautious when visiting petting farms since there is animals such as sheep can be carriers of the Cryptosporidium parvum as identified in lamb faecal sample. Secondly, there will be awareness of personal hygiene particularly washing of hands before eating. There will be communication of risk to pet farm visitors on importance of hygiene. Thirdly, identification of Cryptosporidium parvum lamb faecal sample shows that there is need for more examination of farm animals on the possibility of carrying the Cryptosporidium parvum (Smith and Padfield 2016 ).

Conclusion:

Based on the study, it is clear that the study of cryptosporidiosis outbreak in the UK based petting farm used case-control study design. Case-control research compares visitors with cryptosporidiosis disease as cases with visitors without cryptosporidiosis disease as control. Some of the identified strength of the paper are effective study of rare outbreak disease such as cryptosporidiosis, the paper clearly compare risk exposure to the outcome and study can be used to investigate multiple exposures to risk factors (Burls 2009). The weaknesses of the study paper include biasness in data collection, difficulty in determining of cryptosporidiosis incidence rate in control and cases, and sequence between exposures of farm visitors to risk is not easily established. 

Reference

Burls, A. (2009), What is critical appraisal? London, Hayward Group. Web/URL: https://www.whatisseries.co.uk/what-is-critical-appraisal/ Accessed October 2010.

Boreham J, and Sutherland I (2004), Mortality in relation to smoking: 50 years’ observations on male British doctors. BMJ. 28 (755): 1519

Chalmers, R. and Giles M (2010), Zoonotic cryptosporidiosis in the UK – challenges for control. Journal of Applied Microbiology; 109: 1487–1497

Gargala G, (September 2008), Drug treatment and novel drug target against Cryptosporidium. Parasite: 15 (3): 275–81.

Grimes A, and Schulz, F (2005), Compared to what? Finding controls for case-control studies. Lancet. 365 (9468): 1429–33.

Greenland, S. and Lash, L. (2008), Modern Epidemiology (3rd ed.). Wolters Kluwer: Lippincott Williams & Wilkins.

Hunter, P. and G Nichols (2002), Epidemiology and clinical features of cryptosporidium infection in immunocompromised patients. Clinical Microbiology Reviews 2002; 15: 145–154.

Ioannidis, P. (2005), Contradicted and initially stronger effects in highly cited clinical research. JAMA. 294 (2): 218–28

Kenneth J. and Ray, C. George (2004). An Introduction to Infectious Disease: Sherris Medical Microbiology (4th ed.). New York: McGraw-Hill. pp. 727–730.

Kalam K, and Baqi S et al (2014). “Prevalence, clinical presentation and treatment outcome of cryptosporidiosis in immunocompetent adult patients presenting with acute diarrhoea”. J Pak Med Assoc. 64 (6): 613–8.

Leske M, and Wu SY. (1996) Open-angle glaucoma and ocular hypertension: the Long Island Glaucoma Case-control Study. Ophthalmic Epidemiology. 1996;3:85–96

 Smith S. and Padfield S. (2016) Cryptosporidiosis outbreak in visitors of a UK industry-compliant petting farm caused by a rare Cryptosporidium parvum subtype: a case-control study. Epidemiology and infection 2016;144(05):1000-1009.

Rose, S  and Mark J (2008), Matched case control study design. U.C. Berkeley Division of Biostatistic: Working Paper series. Working paper 240.

Rothman, K. (2002), Epidemiology: An Introduction. Oxford, England: Oxford University Press.

Sparks H, and White AC (2015). “Treatment of Cryptosporidium: What We Know, Gaps, and the Way Forward”. Curr Trop Med Rep. 2 (3): 181–187.

Schulz F, Grimes, A (2002), Case-control studies: research in reverse. Lancet. 359 (9304): 431–4

Toth, T. L., & Hauser, R.et al (2008), Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic, Human Reproduction, vol. 23, no. 11, pp. 2584-2590.