HIV-positive individuals have increased risk of severe malaria

HIV-positive individuals have a significantly increased risk of severe malaria, South African researchers have found. Investigators working at a hospital in Soweto established that the risk of severe malaria was almost three times greater for HIV-positive individuals than HIV-negative ones. The investigators' findings are published in the December 1^st online edition of Clinical Infectious Diseases.

Malaria is endemic in sub-Saharan Africa in countries that also have a high HIV prevalence. The impact of infection with HIV on the severity of malaria is, however, unclear. Therefore, patients admitted to the Chris Hani Baragwanath Hospital in Soweto with malaria were tested for HIV. Patients found to be HIV-positive had their CD4 cell count measured.

Partial immunity to malaria can be obtained through childhood exposure to the malaria parasite. Immunity to malaria was assessed by questioning patients about the area of birth and past residence to see if they had lived in an area where malaria was endemic. Malaria symptoms and severity were also assessed. Severe malaria was diagnosed using standard World Health Organization definitions.

A total of 336 patients were included in the investigators’ analysis. Of these individuals, 110 (33%) were HIV-positive. Two-thirds of patients had semi-immunity to malaria.

The investigators found that HIV-positive patients were almost three times more likely to have severe malaria. They also found that HIV-positive individuals were significantly more likely to have a distinct pattern of illness caused by malaria, including kidney failure, severe anaemia, and that people with HIV were more likely to be admitted to intensive care than HIV-negative malaria patients.

Symptoms of malaria differed between HIV-positive and HIV-negative patients. Those with HIV were less likely to complain of rigors (50% vs 62%, p = 0.05) or headache (69% vs 84%, p = 0.003), but were more likely to experience vomiting (51% vs 35%, p = 0.005) and diarrhoea (31% vs 17%, p = 0.005).

In multivariate analysis, the investigators found that the risk factors for severe malaria were non-immunity (adjusted odds ratio, 5.91), HIV infection (adjusted odds ratio, 4.15), a high malaria parasite count (adjusted odds ratio, 1.38), and an elevated white blood count (adjusted odds ratio, 1.26).

Overall, the investigators noted that HIV-positive patients with a CD4 cell count below 200 cells/mm³ were significantly more likely than HIV-negative individuals to have severe malaria (p 3 vs 190 cells/mm³, p = 0.007) than semi-immune HIV-positive individuals.

“HIV infection is associated with an increased risk of severe malaria”, write the investigators. They offer two possible explanations for this. Either “HIV infection could impair immune responses to malaria parasites”, or “HIV-infected patients may develop excessive or aberrant immune responses that lead to increased disease severity.”

HIV-positive patients were more likely to have unusual symptoms of malaria, which could be mistaken as symptoms of common HIV-related opportunistic infections. The investigators recommend that “clinicians should be aware of this and maintain a high index of suspicion for the diagnosis of malaria in HIV-infected travelers.”