Echocardiographic screening for the identification of subclinical RHD is the gold-standard method for understanding disease burden and severity in endemic regions. Insights from echocardiography-based RHD screening programs are vital to informing advocacy and public health responses to reduce the burden of RHD, however data from sub-Saharan Africa are limited. In this study, we sought to provide insights into the epidemiology and echocardiographic characteristics of subclinical RHD in Tanzanian school-children. We found that subclinical RHD as detected by echocardiographic screening is not uncommon in primary school children in Dar es salaam, uniformly affects the mitral valve, and is associated with potentially modifiable risk factors.
We observed that thirty-two out of 949 screened children were found to have subclinical RHD, including seventeen with definite subclinical RHD. The prevalence of subclinical RHD in this study is comparable to that found in other studies in Africa including: Senegal, Brazzaville, Uganda, Ethiopia, Mozambique and Malawi which ranges between 4.95 per 1000 to 32.6 per 1000.(12–16) Furthermore our findings are very similar to the reported prevalence of subclinical RHD in Malawi with the difference being in the number of definite and borderline cases whereby their study had more borderline cases than definite cases compared to this study. The similarity could be explained by both studies having been conducted in sub-Saharan Africa where sociodemographic characteristics are similar.(12) The number of definite cases in this study was slightly higher than the number of borderline cases which was also demonstrated in the studies done in Eastern Nepal and Mozambique. This is because in all three studies the RHD was more prevalent in children of 9 years of age and above when significant valvular changes have taken place for a definite disease to occur. (13, 17). The prevalence of RHD detected by clinical examination was approximately 1 per 1000 compared to the prevalence detected by echocardiography which was approximately 34 per 1000. Several studies have shown that, regardless of the experience of the examiner, the sensitivity and specificity of echocardiography is greater than cardiac auscultation. (18–20) The early progressive valvular changes in RHD are silent and hence it is difficult to pick them by cardiac auscultation unless they are visualized by echocardiography.
In this study, all the participants who were found to have RHD had mitral valve disease without involvement of any other valve. Typical features of mitral valve disease observed in our study include regurgitation, AMVL thickening, chordal thickening and excessive mitral valve leaflet motion. Several studies from Sub-Saharan African have highlighted the predominance of mitral valve disease among individuals with subclinical RHD. Other studies have shown that aortic valve disease may be associated with mitral valve disease though only in a small percentage of individuals. (5, 21) Pure mitral stenosis is commonly seen in the third decade of life and given that our study population was all less than the age of 17, we did not observe a high prevalence of rheumatic mitral stenosis as would be expected in this younger population (22). This pattern is similar to that seen by Chimalizeni et al in Malawi school children screened whereby mitral regurgitation was the most common valvular lesion, there was only one child with aortic valve disease and there was no mitral stenosis.(12) Moreover, this finding is in agreement with other RHD echocardiographic screening studies in Cambodia, Mozambique and Senegal which also were conducted in school children to determine the prevalence of subclinical RHD that showed that the mitral valve was the most affected valve although it was associated with aortic valve disease and without the presence of mitral stenosis.(13, 14) In subclinical RHD, mitral stenosis is not a common lesion of mitral valve disease as it has not been reported in several studies except the screening done in school children from Ethiopia where mitral stenosis was found in only 7% of children. (16) The mitral valve is more commonly involved in RHD probably because the mitral valve cusps are exposed to the pressure of the left ventricle during contraction in systole but the aortic cusps are exposed to the aortic diastolic pressure during closure and so the shear stress on the large mitral leaflets is more than on the small aortic cusps thus making the mitral valve more prone to injury during the RF attacks. The findings of the current study have important implications for the design of future echocardiographic screening studies that could be directed at only the mitral valve in resource-limited settings.
Multiple studies from Sub-Saharan African, including Mozambique, Uganda, Senegal, and Malawi, have observed that children above the age of 9 have a higher observed prevalence of subclinical RHD compared to younger.(12–15, 17) At an older age of 9 years and above, there are notable valvular changes after the child has had a number of RF attacks. Although the development of RHD is associated with poor hygiene(23), few studies have examined the association between hygiene, respiratory tract infections, and RHD. Not adhering to handwashing practices has been associated with predisposing a child to streptococcal infections like impetigo which is regarded as a risk factor for URTI (23). In a systematic review by Wilson et al exploring the impact of simple hygiene interventions introduced in primary schools and day care centres on respiratory and gastrointestinal infections, it was found that hand hygiene can reduce the incidence of URTI.(24) In Pakistan, poor hygienic conditions was reported as a major risk factor for RF and RHD, however, their sample size was smaller compared to this study and included only children diagnosed with acute rheumatic fever or RHD in the outpatient clinic by echocardiography. (23) Our findings are also consistent with those reported by Ngaide et al from Senegal and Vlajinac H et al in Yugoslavia, where repeated sore throat was observed to be a predisposing factor for the development of RHD especially for those who had definite RHD by echocardiography. (14, 25) Similarly, in the present study, we observed that children aged more than 9 years, recurrent URTI, and poor hygiene were associated with prevalent RHD. Our results highlight the importance and relevance of current guidelines and expert opinion regarding the prevention of rheumatic fever and rheumatic heart disease through the prompt recognition and treatment of GAS pharyngitis, supporting access to clean water for adequate hygiene, and access to healthcare. (29, 30)