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defined as younger than 15 years of age and adults as 15 years or older. To facilitate the reporting of HIV infection, WHO recommends the following: HIV cases diagnosed and not previously reported in each country should be reported according to a standard national case definition. A case of HIV infection is defined as an individual with HIV infection irrespective of clinical stage (including severe or stage 4 clinical disease, also known as AIDS) confirmed by laboratory criteria according to country definitions and requirements. Countries should develop and regularly review their testing algorithms for diagnostic and surveillance purposes.i WHO provides a simplified HIV case definition designed for reporting and surveillance. HIV infection is diagnosed based on laboratory criteria. Clinically diagnosing suspected or probable HIV infection by diagnosing an AIDS-defining condition or HIV at any immunological stage in an adult or child requires confirmation of HIV infection by the best age-appropriate test. Further, as maternal HIV antibody transferred passively during pregnancy can persist for as long as 18 months among children born to mothers living with HIV, positive HIV antibody test results are difficult to interpret in younger children, and alternative methods of diagnosis are recommended. Box 1. WHO case definition for HIV infection Adults and children 18 months or older HIV infection is diagnosed based on: positive HIV antibody testing (rapid or laboratory-based enzyme immunoassay). This is confirmed by a second HIV antibody test (rapid or laboratory-based enzyme immunoassay) relying on different antigens or of different operating characteristics; and/or; positive virological test for HIV or its components (HIV-RNA or HIV-DNA or ultrasensitive HIV p24 antigen) confirmed by a second virological test obtained from a separate determination. Children younger than 18 months: HIV infection is diagnosed based on: positive virological test for HIV or its components (HIV-RNA or HIV-DNA or ultrasensitive HIV p24 antigen) confirmed by a second virological test obtained from a separate determination taken more than four weeks after birth1 . Positive HIV antibody testing is not recommended for definitive or confirmatory diagnosis of HIV infection in children until 18 months of age. Cases diagnosed with advanced HIV infection (including AIDS) not previously reported should be reported according to a standard case definition. Advanced HIV infection is diagnosed based on clinical and/or immunological (CD4) criteria among people with confirmed HIV infection. Criteria for diagnosis of advanced HIV (including AIDS a) for reporting Clinical criteria for diagnosis of advanced HIV in adults and children with confirmed HIV infection: presumptive or definitive diagnosis of any stage 3 or stage 4 condition. and/or; Immunological criteria for diagnosing advanced HIV in adults and children five years or older with confirmed HIV infection: CD4 count less than 350 per mm3 of blood in an HIV-infected adult or child. and/or; Immunological criteria for diagnosing advanced HIV in a child younger than five years of age with confirmed HIV infection: %CD4+ <30 among those younger than 12 months; %CD4+ <25 among those aged 12–35 months; %CD4+ <20 among those aged 36–59 months. There is no standard definition of primary HIV infection. However, reporting primary HIV infection, where recognized and documented, is useful and should be encouraged. The United States Centers for Disease Control and Prevention (CDC) are expected to develop a case definition for reporting primary HIV infection. Primary HIV infection can be recognized in infants, children, adolescents and adults; it can be asymptomatic or be associated with features of an acute retroviral syndrome of variable severity. Primary infection usually presents as an acute febrile illness 2–4 weeks postexposure, often with lymphadenopathy, pharyngitis, maculopapular rash, orogenital ulcers and meningoencephalitis. Profound transient lymphopaenia (including low CD4) can develop, and opportunistic infections may occur, but these infections should not be confused with clinical staging events developing in established HIV infection. Primary HIV