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HIV infection is often difficult to diagnose in very young children. Infected babies, especially in the first few months of life, often appear normal and may exhibit no telltale signs that would allow a definitive diagnosis of HIV infection. Moreover, all children born to infected mothers have antibodies to HIV, made by the mother's immune system, that cross the placenta to the baby's bloodstream before birth and persist for up to 18 months. Because these maternal antibodies reflect the mother's but not the infant's infection status, the test is not useful in newborns or young infants.

In recent years, investigators have demonstrated the utility of highly accurate blood tests in diagnosing HIV infection in children 6 months of age and younger. One laboratory technique called polymerase chain reaction (PCR) can detect minute quantities of the virus in an infant's blood. Another procedure allows physicians to culture a sample of an infant's blood and test it for the presence of HIV.

Currently, PCR assays or HIV culture techniques can identify at birth about one-third of infants who are truly HIV-infected. With these techniques, approximately 90 percent of HIV-infected infants are identifiable by 2 months of age, and 95 percent by 3 months of age. One innovative new approach to both RNA and DNA PCR testing uses dried blood spot specimens, which should make it much simpler to gather and store specimens in field settings.

Progression of HIV Disease in Children

Researchers have observed two general patterns of illness in HIV-infected children. About 20 percent of children develop serious disease in the first year of life; most of these children die by age 4 years.

The remaining 80 percent of infected children have a slower rate of disease progression, many not developing the most serious symptoms of AIDS until school entry or even adolescence. A recent report from a large European registry of HIV-infected children indicated that half of the children with perinatally acquired HIV disease were alive at age 9. Another study, of 42 perinatally HIV-infected children who survived beyond 9 years of age, found about one-quarter of the children to be asymptomatic with relatively intact immune systems.

The factors responsible for the wide variation observed in the rate of disease progression in HIV-infected children are a major focus of the NIAID pediatric AIDS research effort. The Women and Infants Transmission Study, a multisite perinatal HIV study funded by NIH, has found that maternal factors including Vitamin A level and CD4 counts during pregnancy, as well as infant viral load and CD4 counts in the first several months of life, can help identify those infants at risk for rapid disease progression who may benefit from early aggressive therapy.

Signs and Symptoms of Pediatric HIV Disease

Many children with HIV infection do not gain weight or grow normally. HIV-infected children frequently are slow to reach important milestones in motor skills and mental development such as crawling, walking and speaking. As the disease progresses, many children develop neurologic problems such as difficulty walking, poor school performance, seizures, and other symptoms of HIV encephalopathy.

Like adults with HIV infection, children with HIV develop life-threatening opportunistic infections (OIs), although the incidence of various OIs differs in adults and children. For example, toxoplasmosis is seen less frequently in HIV-infected children than in HIV-infected adults, while serious bacterial infections occur more commonly in children than in adults. Also, as children with HIV become sicker, they may suffer from chronic diarrhea due to opportunistic pathogens.

Pneumocystis carinii pneumonia (PCP) is the leading cause of death in HIV-infected children with AIDS. PCP, as well as cytomegalovirus (CMV) disease, usually are primary infections in children, whereas in adults these diseases result from the reactivation of latent infections

.A lung disease called lymphocytic interstitial pneumonitis (LIP), rarely seen in adults, also occurs frequently in HIV-infected children. This condition, like PCP, can make breathing progressively more difficult and often results in hospitalization.

Children with HIV suffer the usual childhood bacterial infections -- only more frequently and more severely than uninfected children. These bacterial infections can cause seizures, fever, pneumonia, recurrent colds, diarrhea, dehydration and other problems that often result in extended hospital stays and nutritional problems.

HIV-infected children frequently have severe candidiasis, a yeast infection that can cause unrelenting diaper rash and infections in the mouth and throat that make eating difficult.

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