Estimating the post-neonatal prevalence of sickle cell disease in a Brazilian Population

OBJECTIVE: To estimate the prevalence of individuals with sickle cell disease (SCD) in Aracaju, Brazil, using the capture-recapture (CRC) method. SCD is a significant public health problem with long-term life-threatening complications. There are no reliable estimates of the number of individuals with this condition in Aracaju, north-east Brazil. The CRC method has been used to quantify other ubiquitous populations. METHOD: Three independent lists of individuals with homozygous (HbSS) SCD were constructed from patients attending the main specialist ambulatory service, all patients with SCD admitted to three government hospitals and a clinic providing specialist immunisation services to patients with SCD. Individuals were matched to ascertain whether they appeared in one, two or three lists, and population size was estimated using the log-linear model. RESULTS: The lists identified 374 individuals. Two hundred and one appeared in one, 99 in two and 74 in three lists with an estimated number 400 (95% CI 387-418) HbSS SCD individuals; 51.6% patients with SCD were men and age ranged from 1-62 years (median 14). CONCLUSION: The CRC method resulted in a smaller population estimate than expected. The causes of this discrepancy may include list dependence, high mortality with a survival cohort effect and the method of identifying the more severe cases. The CRC method has potential to estimate the size of this population and could supplement neonatal screening to further characterise the SCD population in this region.