DEFINITIONS AND EPIDEMIOLOGY
Infection with the human immunodeficiency virus (HIV) induces a secondary immune deficiency, rendering the host susceptible to infection. The immunosuppressive combination of HIV infection in the setting of the immature pediatric immune system represents an ideal medium for opportunistic pathogens to thrive, and the challenge rests with the pediatrician to diagnose, treat, and prevent these infections.
Infections in HIV-infected children occur in two broad groups: opportunistic infections and nonopportunistic infections. Opportunistic infections are defined by the Centers for Disease Control and Prevention (CDC) disease classification of pediatric HIV infection (see Table 57-1 in Chapter 57, on care of the HIV-infected child).1 Non-opportunistic infections represent all other known pathogens. The description of an infection as an opportunistic infection is helpful in defining an AIDS-related illness, but does not mean that the nonopportunistic infections are any less common or severe.
In the United States, earlier detection of HIV infection through screening of pregnant women, postnatal testing of HIV-exposed infants, as well as the early institution of combination antiretroviral therapy (cART) and Pneumocystis prophylaxis, have dramatically decreased the rates of AIDS-related opportunistic infections in children. These advances have changed pediatric HIV in most children from an acute life-threatening condition to a chronic illness. Despite these advances, opportunistic infections continue to occur in this population.
The epidemiology of infections in the HIV-infected child in the United States was dramatically transformed after the introduction of cART in 1996 and its subsequent widespread use. In the pre-cART era, the five most common opportunistic infections, all of which occurred at an event rate of greater than 1 per 100 patient-years, were serious bacterial infection, herpes zoster, and disseminated Mycobacterium avium complex (MAC), Pneumocystis jiroveci pneumonia (PCP, formerly called Pneumocystis carinii pneumonia), and mucosal candidiasis (Table 58-1).2 Other less common opportunistic infections included cytomegalovirus (CMV) disease (particularly retinitis), tuberculosis, invasive fungal disease, toxoplasmosis, and progressive multifocal leukoencephalopathy (PML). In the cART era, opportunistic infections occur mainly in two settings: as the presenting sign of a child in whom the diagnosis of HIV was previously unknown, and in known HIV-infected children with a persistently low CD4+ T-lymphocyte percentage.3 In the years following the introduction of cART, the four most common opportunistic infections, all of which occurred at a lower event rate than during the pre-cART era, were bacterial pneumonia, herpes zoster, oral candidiasis, and dermatophyte infections (Table 58-1).4
TABLE 58-1Overall Incidence Rates of Most Common First-time Infections in HIV-infected Children in the United States Before and After the Introduction of cART |Favorite Table|Download (.pdf) TABLE 58-1 Overall Incidence Rates of Most Common First-time Infections in HIV-infected Children in the United States Before and After the Introduction of cART
|Infection Type ||Pre-cART ||cART Era |
|Opportunistic infection category ||Incidence rate of events/100 person-years (95% CI) ||Incidence rate of events/100 person-years (95% CI)...|