Sickle Cell Anaemia in East Africa: Preliminary Results from a Cohort Study.

Background: The recognition of Sickle cell anaemia (SCA) as a problem of public health significance by the world health organisation in May 2006 has major implications in Africa where an estimated 300,000 children are born every year. In Tanzania, 20% of the population are heterozygous for the S Gene; up to 10,000 children are born every year with SCA. In order to target limited resources, research and interventional programmes require the identification of problem areas that will need to have maximum impact. Despite the protection against malaria in heterozygous individuals, paradoxically malaria is thought to be a common cause of morbidity and mortality in SCA. Bacterial infections have been implicated as a common cause of mortality and Transcranial Doppler ultrasonography (TCD) has been used to identify patients at increased risk of stroke, a recognised cause of morbidity.

Aims: The study attempts to define causes of morbidity and mortality in SCA in Tanzania focusing on three major areas where it is important to establish clear answers. The aims of the study are to determine the role of malaria infection in SCA patients, to describe the major bacterial pathogens associated with admission in SCA patients and to describe the spectrum of cerebral blood flow velocities (CBFv) using TCD in SCA patients in East Africa.

Study design: This is a prospective, descriptive cohort study in Muhimbili national hospital, Dar-es-salaam, Tanzania with clinical surveillance of patients in outpatient clinic every three months and during admission to hospital for any acute clinical event.

Results: From March 2004 to June 2006, there have been 5,601 visits during which clinical and laboratory data has been collected on 1,000 (male 51.4%) SCA patients. The mean age of the patients is 10 7.4 years, (range 7 months54 yrs), with 91.7% below 20 years of age; 8.28% under the age of 5 years. The frequency of major clinical events, including fits (5.2%), stroke (1.9%) is reported. The prevalence of malaria parasitaemia in outpatients and during admission was 2.9% and 7.7% respectively which was lower than in the non-sickle population. There have been 516 admissions during this period, presenting with pain (44%), anaemia (17%) and fever (15%). Salmonella species (Non typhoid salmonella) was the commonest bacterial pathogens isolated. TCD was done in 400 patients (age 2 – 16 years); with 25% having a time averaged maximal mean velocity of 150 cms/second or more, suggesting stenosis.

Conclusion: Preliminary analysis suggest over 90% of the SCA population are under 20 years of age, with a deficit in the under 5 year age group. There is reduced malaria infection, suggesting resistance to malaria and not susceptibility as previously reported. Painful crises were the commonest cause of admission with salmonella the most frequent pathogen isolated. TCD identified at least 25% of patients with CBFv suggestive of stenosis. This study is the initial step in describing the causes of morbidity in patients with SCD disease in Tanzania and will form the basis of longitudinal studies that will attempt to guide interventional strategies, target research and provide insight into natural history of SCD in East Africa.