|LETTER TO EDITOR
|Year : 2015 | Volume
| Issue : 2 | Page : 157
Rheumatic heart disease: Sample size issues in low prevalence scenario and the role of echocardiography
Renu Chauhan1, Rajesh Kumar2
1 Department of Community Medicine, Dr. Rajendra Prasad Government Medical College, Kangra, Tanda, India
2 Department of Surgery, Indira Gandhi Medical College, Shimla, Himachal Pradesh, India
|Date of Web Publication||30-Jul-2015|
Department of Community Medicine, Dr. Rajendra Prasad Government College, Kangra, Tanda - 176 001, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chauhan R, Kumar R. Rheumatic heart disease: Sample size issues in low prevalence scenario and the role of echocardiography. Nig J Cardiol 2015;12:157
We read the article, "Clinical screening for heart disease in apparently healthy Nigerian school children",  published in your journal with great interest. In this regard, we have the following points to make:
The sample size used for determining the prevalence of rheumatic heart disease (RHD) was highly inadequate as a result of which no RHD case could be detected among the study population. The authors mention that because of lack of information of prevalence rates of heart diseases among children from the study area, 50% prevalence was assumed (0.05 chosen margin of error), and a small sample size of 381 was reached. However, this method may not be appropriate for diseases with low prevalence as larger sample sizes are required for identifying even single cases of disease, and for rarer conditions like RHD, ever larger sample sizes would be required.  Studies with small sample sizes may fail to yield any cases of the disease. In such circumstances, when an estimate of prevalence is not available for a particular study area, then prevalence estimates from research studies at the country or regional level could be used while determining the sample size. However in doing so, due consideration must be given to factors such as study design, socio-economic status, cultural and genetic variations that could affect disease prevalence and the proportions from the most recent studies should be used. Although the authors have expressed this as a limitation of the study, the results are misleading and can create an impression of decline in prevalence of RHD in the study area, which may not be true
The diagnosis of rheumatic fever (RF) is mainly clinical. The authors have not mentioned whether Jones criteria were used for the diagnosis of RF. Also, patients suffering from RF are more likely to miss school because of their illness, and in turn get left out from the study. They need to be actively retrieved by home visits. These factors may have resulted in missing possible cases of RF and RHD, as has been acknowledged by the authors
The role of echocardiography in the diagnosis of RF/RHD is well established. It is more sensitive and specific than auscultation, and is also able to identify subclinical rheumatic carditis, which may go unnoticed on routine clinical examination.  Echocardiography has been used in the diagnosis of heart disease in the present study among the clinically suspected cases who presented with abnormal cardiovascular findings. However, the yield of RHD could be increased further by screening all the school children with echocardiography instead of subjecting them to clinical examination first and then performing echocardiography on the clinically suspect cases only.
| References|| |
Yilgwan CS, Ige OO, Bode-Thomas F. Clinical screening for heart disease in apparently healthy Nigerian school children. Nig J Cardiol 2014;11:74-9.
Naing L, Winn T, Rusli BN. Practical issues in calculating the sample size for prevalence studies. Arch Orofac Sci 2006;1:9-14.
Ramakrishnan S. Echocardiography in acute rheumatic fever. Ann Pediatr Cardiol 2009;2:61-4.