Critical Appraisal of a Paper

The essay deals with the critical appraisal of the paper “Cryptosporidiosis outbreak in visitors of a UK industry-compliant petting farm caused by a rare Cryptosporidium parvum subtype: a case-control study” by (Utsi et al. 2016) and includes the analysis of the strength and weakness of the study along with the appropriateness of the study design and method of investigation. Based on the critical review the author finally draws a conclusion about the study.

The purpose of the study is to understand the Cryptosporidium infection and it’s mechanism of transmission in an outbreak that occurred in the petting farm in England. The purpose of this study is to communicate the risks of infection to the farm visitors and prevent the future Cryptosporidium outbreaks.

The researcher has conducted the case-control study for investigating Cryptosporidium outbreaks. The investigation also includes environmental and microbiological analysis. This study design is justified bec

The researcher has used the snowball sampling to investigate 32 cases and 32 controls. There was a total of 22 cases in which Cryptosporidium parvum gp60 subtype was found to be present in lamb fecal particles. The target population was mainly farm visitors. The sample selected had the illness in the fourteen days after they visited the farm with abdominal pain, fever, and vomiting being prominent. The secondary cases included non-visitors to the farm and showed symptoms after contact with the primary cases. 

The sample is representative of the target population as the farm visitors were the at-risk population. However, the immediate relatives of the cases were not representative of the target population as there is a chance of underestimating the risk association due to misclassification. The researcher should not have used non-random sampling technique as it includes number of potential issues as it is a case-control study (2)

The researcher has collected information related to factors of the outbreak using web-based survey method and questionnaires as a primary instrument. The study includes flexibility for the participants as they are allowed to respond either by telephone or email as per the choice. The information was obtained by involving the risk factors in the study and investigating the outcome. The outcome factors were then traced back to exposures.

In this study, the key confounder may be the close food and water interaction. Also, there may be direct contact with the animal as Cryptosporidium parvum gp60 subtype was found to be present in lamb fecal particles. The immediate relatives of the confirmed cases may have diarrhea before due to an absence of adequate toilet facilities. However, the researcher has investigated the cleanliness of the animal to adjust the confounders and the hand washing facilities. The other confounders such as people living in the same locality having diarrhea and other factors were not managed. Children may also drink water while bathing that may have confounding effects. In conclusion, all the confounders were not managed (3).

The potential factor of bias includes engaging both laboratory-confirmed as well as probable cases leading to misclassification. Further, the control group too may contain asymptomatic carriers that will reduce the true identification of the risk factors. Conclusively, this may affect the risk elimination in people by effecting the number of the people seeking healthcare.

The statistical analysis involved in this study was Multivariable logistic regression where the results were tested for significance at 95% confidence interval. It is appropriate for the study to link the criterion with and several predictors. However, there should be larger sample population for each set of explanatory variable (4). According to (5) logistic regression provides the strength of the association with a quantified value.

The result findings revealed that Cryptosporidium infection is transmitted due to eating without washing hands in open farms. The major risk of the infection is the lack of verbal information given to the farm visitors in the petting farm. Therefore, risk awareness and hand hygiene are essential factors in determining infection.

The researcher has well presented the purpose and objective of the study along with background and significance. The strength of the study is the statistical significance of the results as well as implies health importance that may be beneficial in eliminating future risks by staff supervision and training. However, non-random sampling technique is the limitation of the study as it includes a chance of misclassification in this case study. Further, (6) conducted similar studies believed that asymptomatic carriers may lead to underestimation of true risk exposure and association. The researcher has carefully reviewed previously collected data related to cryptosporidiosis outbreaks and identified its drawbacks. The drawbacks were eliminated in this study which constitutes the strength of the study. According to (7), case-control studies may not generate valuable information if the study is subjected to bias and also it does not generate incidence data.

The weakness of the case-control study is that it cannot clearly establish the temporal relationship between the effect and the supposed cause (8). Further limitations include restriction of the sample to those identified through the routine surveillance methods. It may lead to underestimation of the actual size of the outbreak. Sample size appears to be other weakness in this study. According to (9), limited sample size decreases the chance of detecting the significant risk association. 

Considering the strength and weakness of the study, it can be concluded that the results are not valid. The researcher has not intended to adjust the confounders which are the most preferred method of multivariate analysis in non-randomized studies (10). The study demonstrates association but not the causation of the zoonotic infection. The researcher, however, did not highlight the validity of the research methods.

The author concludes that the hygiene compliance and risk awareness in farm visitors can address the challenge of infection due to cryptosporidiosis. As a critique, I agree with the study conclusion. Assuming the results to be valid, it may have positive implication for the public health. Dissemination of the results is effective in communicating the risk factors and helps develop strategies to minimize the adverse outcomes. Conclusively, the research paper has identified the association of the risk but not the causation. The essay has presented the merits and demerits of the study and has enlightened my knowledge about case-control studies. This will be useful in conducting systematic review and meta-analysis in future.

References

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2. Del Coco VF, Córdoba MA, Bilbao G, de Almeida Castro AP, Basualdo JA, Fayer R, Santín M. Cryptosporidium parvum GP60 subtypes in dairy cattle from Buenos Aires, Argentina. Research in veterinary science. 2014 Apr 30;96(2):311-4.
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10. Utsi L, Smith SJ, Chalmers RM, Padfield S. 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 Apr 1;144(05):1000-9.