Inclusion Criteria:  HIV-infected children aged 1 to 59 months admitted at Mwanamugimu Nutrition Unit with severe acute malnutrition HIV exposed but uninfected children aged 1 to 59 months admitted at Mwanamugimu Nutrition Unit with severe acute malnutrition For prevalence of HIV-infection sub-study, children presenting with severe acute malnutrition on admission at Mwanamugimu Nutrition Unit. For PK sub-study, the child should have been on antiretroviral therapy for at least 2weeks and should have been in hospital for at least 2weeks.  Exclusion Criteria:  For PK sub-study; a child with documented poor adherence to antiretroviral therapy. For PK sub-study; a child known to have vomited the drug on the sampling day.