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CORRESPONDENCE
Year : 2020  |  Volume : 152  |  Issue : 1  |  Page : 146-148

A critical appraisal of a case-control study on healthcare workers


Department of Community Medicine, Bharati Vidyapeeth Medical College, Pune 411 043, Maharashtra, India

Date of Submission14-Jul-2020
Date of Web Publication17-Sep-2020

Correspondence Address:
Trishna Mohanty
Department of Community Medicine, Bharati Vidyapeeth Medical College, Pune 411 043, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijmr.IJMR_3025_20

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How to cite this article:
Mohanty T, Doke PP. A critical appraisal of a case-control study on healthcare workers. Indian J Med Res 2020;152:146-8

How to cite this URL:
Mohanty T, Doke PP. A critical appraisal of a case-control study on healthcare workers. Indian J Med Res [serial online] 2020 [cited 2021 Apr 17];152:146-8. Available from: https://www.ijmr.org.in/text.asp?2020/152/1/146/292092



Sir,

We read the article with interest by Chatterjee et all, published recently and want to congratulate the authors for conducting this study in such a short span of time during this pandemic. We would like to contribute a few points.

In this study, controls are taken in less number than cases. During a case-control study, the desired ratio between cases and controls should be at least 1:1 and preferably may be 1:2 or even 1:3[2]. This study was most appropriate to have 1:2 or 1:3 ratio as only a small proportion of healthcare workers (HCWs) were affected. Matching is usually done for age and sex between cases and controls[3]. Only symptomatic persons were considered in this study for cases and controls. Asymptomatic cases were not considered which constitute 40-45 per cent of the infective cases[3]. Hence, selection bias must have been introduced vitiating results. The proportion of non-responders is extremely high ranging from 32 to 40 per cent. The number of participants who completed interview was far less than the minimum required number. It is likely that the history of consuming hydroxychloroquine (HCQ) may be different among them. It is usual experience that non-respondents are either from uppermost or lowermost quartile[4]. High non-response rate certainly vitiates the results. The time period of enrolment and data collection constitutes approximately seven weeks. Chatterjee et al[1] have not given precise information about details of consumption of HCQ. Initial guidelines were to take HCQ for seven weeks. There may be some HCWs who consumed HCQ for more than six weeks but stopped after that. The effect will be washed off. It was also not clear if the consumption history was at the time of telephonic interview or at the time of collection of sample. It could have been mentioned clearly. When adjusted odds ratio was calculated, there was no need to give crude odds ratio in the first few Tables. Further, the risk-benefit ratio of HCQ administration needs to be closely examined and this could have been easily done. It has major side effects such as retinal disorders, prolongation of QT interval and haemolytic anaemia[5].

These are the few observations and comments from my side.

Conflicts of Interest: None.



 
   References Top

1.
Chatterjee P, Anand T, Singh KJ, Rasaily R, Singh R, Das S, et al. Healthcare workers & SARS-CoV-2 infection in India: A case-control investigation in the time of COVID-19. Indian J Med Res 2020; 151 : 459-67.  Back to cited text no. 1
    
2.
Celentano DD, Szklo M. Observational Studies. Gordis epidemiology. 6th ed. Philadelphia: Elsevier; 2018. p. 167-9.  Back to cited text no. 2
    
3.
Oran DP, Topol EJ. Prevalence of asymptomatic SARS-CoV-2 infection: A narrative review. Ann Intern Med 2020; M20-3012.   Back to cited text no. 3
    
4.
National Research Council. Nonresponse bias. In: Tourangeau R, Plewis TJ, editors. Nonresponse in social science surveys: A research agenda. Washington, DC: The National Academies Press; 2013. p. 40-50.  Back to cited text no. 4
    
5.
D'Cruz M. The ICMR Bulletin on targeted hydroxychloroquine prophylaxis for COVID-19: Need to interpret with caution. Indian J Med Ethics 2020; 5 : 100-2.  Back to cited text no. 5
    




 

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