The information from the study could lead to new ways to prevent and treat severe anaemia in African children, researchers say.
Interestingly, folate and iron deficiencies, which are widely believed to be the most common causes of severe anaemia in African children, were actually not prominent causes, according to Dr. Job C. J. Calis, from the Academic Medical Centre in Amsterdam and colleagues.
They examined the causes of anaemia by conducting a case-control study of 381 severely anaemic preschool-age children and 757 children without anaemia. The subjects were drawn from both urban and rural settings in Malawi.
The strongest risk factor for severe anaemia, which raised the risk by more than fivefold, was bacterial invasions of the blood or "bacteremia," Calis and colleagues report in Thursday's edition of The New England Journal of Medicine.
Other significant risk factors included malaria, hookworm infection, HIV infection, vitamin A deficiency, and vitamin B12 deficiency.
Further analysis showed that malaria was a risk factor only in urban settings, not in rural settings. The majority of hookworm infections (76 percent) involved children younger than age two.
Folate deficiency, sickle cell disease, and laboratory signs of inflammation were not commonly seen. Similarly, relative few case patients had iron deficiency and its presence was actually associated with a decreased risk of the major risk factor - bacterial infection.
"Our findings indicate that even in the presence of malaria parasites, additional or alternative diagnoses (responsible for severe anaemia) should be considered," Calis and colleagues write. The results, "if confirmed in different settings, will contribute to the assessment of new therapeutic and preventive strategies for Africa."