Human immunodeficiency virus

OVERVIEW: What every practitioner needs to know

Are you sure your patient has human immunodeficiency virus? What are the typical findings for this disease?

In pediatrics, human immunodeficiency virus (HIV) infection primarily occurs in two patient populations: infants and children who acquired the virus from their mother during gestation or in the perinatal period, and adolescents who acquired the virus through adult risk behaviors (i.e., sex or recreational drug use). Transmission through exposure to blood products has been virtually eliminated through screening of blood donors.

Infants with perinatally acquired HIV are typically asymptomatic at birth, but >90% develop symptoms by 3 years of age if untreated. Adolescents who acquire HIV may experience an acute retroviral syndrome within 2-6 weeks of infection, but symptoms resolve spontaneously within several weeks; many youth enter a period of “clinical latency” with minimal, if any, symptoms for years, while others develop symptoms within 1-2 years.

If untreated, HIV continues to replicate at detectable levels in the blood and other reservoirs in the body, and the level of CD4+ T-lymphocytes, the major target ofHIV infection, eventually declines; when the CD4 cell count becomes severely depleted, symptoms of the Acquired Immunodeficiency Syndrome (AIDS) develop. AIDS is a clinical diagnosis defined by the presence of certain opportunistic infections, malignancies, and HIV-associated central nervous system disease (Table I).

Table I:

Treatment of HIV with antiretroviral therapy (ART) is effective but most of the drugs have potential toxicity and strict adherence to the medication regimen is demanding.

There are two types of HIV, HIV-1 and HIV-2, which have similar clinical courses, although HIV-2 is generally less aggressive. HIV-2 is predominantly found in West Africa, and is rare elsewhere in the world. This monograph will use “HIV” to refer to HIV-1, the type found in the United States (US), and will primarily cover HIV disease as it presents and is treated in high-resource settings such as in the United States and Europe.

Typical findings for HIV infection

A combination of nonspecific but recurrent or persistent symptoms should prompt consideration of HIV infection, such as:

– oral candidiasis

– generalized lymphadenopathy (axillary adenopathy is especially indicative)

– hepatosplenomegaly

– recurrent otitis media and/or sinusitis

– recurrent diarrhea

– intermittent fever

– poor growth or weight loss

– or developmental delay or regression.

Involvement of the central nervous system is more commonly seen in HIV-infected children than adults, and may be subtle (e.g., developmental delay) to more significant (symmetric motor dysfunction, acquired microcephaly or cognitive decline). With advanced disease, symptoms suggestive of severe immunodeficiency ensue, such as wasting, encephalopathy, opportunistic infections and/or unusual malignancies.

Natural history

Before highly active therapy was available, children presented with one of three patterns of HIV disease: rapidly progressive, slowly progressive, or non-progressive. Rapidly progressive disease, occurring in 15-25%,manifested with early onset of failure to thrive, opportunistic infections and encephalopathy in the first year of life and a median untreated life expectancy of less than 1-2 years; this pattern is still common in resource-limited countries (such as sub-Saharan Africa and southeast Asia) where access to therapy is limited but growing.

Slowly progressive disease, which accounted for most (60-80%) children in high-resource countries, manifested with less acute symptoms and a median survival of 6 years. The most common symptom complexes for these children included recurrent bacterial infections (bacteremia/sepsis or pneumonia with S. pneumoniae, Salmonellasp., H. influenzaeor other encapsulated organisms, or otitis media with chronic drainage, or sinusitis), generalized lymphadenopathy, or lymphocytic interstitial pneumonitis (LIP, see below).

Long-term non-progressors (<5% of children) had minimal, if any, symptomatology, a low virus burden and good immunologic function in the absence of treatment; their life expectancy was at least 8 years, and usually much longer.

Initiation of antiretroviral therapy early in life has made rapidly progressive disease uncommon.

While the course of disease is similar to that in adults, adolescents frequently come to medical attention later in the course of illness with more advanced immunodeficiency. Thirty to 60% may experience an acute retroviral syndrome with spontaneous resolution of symptoms; thereafter there is an asymptomatic period which may extend from 6 months to years, followed by moderate symptoms of immunocompromise, such as recurrent or persistent oral or vaginal candidiasis, recurrent or multidermatomal herpes zoster, persistent low grade fever or diarrhea. AIDS-defining conditions (See Table I) occur when the CD4 count has significantly declined, with the greatest risk at <75 CD4 cells/mm³.

Staging of HIV disease

An HIV classification system is used by the Centers for Disease Control and Prevention (CDC) to stage the disease for surveillance and research purposes (Table II).

TABLE II.

For adolescents and adults, the system primarily uses the CD4+ T lymphocyte count (measured as cells/mm³ blood) and relies less on clinical symptoms: Stage 1 is a CD4 count or percentage of >500 cells/mm³ or >29%, stage 2, 200-499 cells/mm³ or 14-28%, and stage 3, <200 cells/mm³ or <14%. Stage 3 disease fits the case definition for AIDS, which also can be fulfilled by diagnosis of an AIDS-defining condition.

The classification for children <13 years of age (Table III) incorporates clinical findings into all of the stages, with categories N, A and B describing no, mild or moderate signs and symptoms, respectively, and C including AIDS-defining diagnoses. The immunologic categories rely more heavily on CD4 percentage than absolute number in children, as absolute CD4 numbers are very high at birth and slowly decline to adult levels ~6 years of age, while the CD4 percentage remains stable throughout that period.

Immunologic categories 1 (no suppression), 2 (moderate suppression) and 3 (severe suppression) use cut-offs of >25%, 15-25% and <15% of CD4+ T-lymphocytes. Therefore, a child’s CDC stage is a combination of clinical and immunologic categories, for example, A2 describes a child with mild symptoms and moderate CD4 suppression.

To monitor overall disease status and response to therapy, clinicians monitor the plasma viral load, or HIV-1 RNA level, measured as number of viral copies/ml blood, and the CD4 count to indicate the immunologic status and need for prophylaxis to prevent AIDS-defining infections. The goal of therapy is to render the viral load undetectable (<50 copies/ml) and restore the CD4 count to >25% (or >500 cells/mm³ for adolescents), as well as to reduce morbidity/mortality and improve the patient’s quality of life.

What other disease/condition shares some of these symptoms?

Other immunodeficiency diseases may present with similar symptoms, for example, severe combined immune deficiency (SCID), CD40 or CD40 ligand deficiency (formerly called Hyper-IgM syndrome), X-linked agammaglobulinemia, common variable immunodeficiency, and chronic mucocutaneous candidiasis. Severe malnutrition, typically seen only in resource limited countries, may have a similar presentation with cachexia, oral thrush and overwhelming infections.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

Diagnostic Testing for HIV Infection

Diagnostic testing should be performed on whole blood, serum or plasma and varies by age. Note that any positive test must be confirmed with a repeat age-appropriate assay from a separate blood sample drawn at a different time before a definitive diagnosis can be made.

Children >18 months, adolescents and adults: HIV antibody testing OR two positive HIV rapid tests made by different manufacturers should be performed. The first tests should be 4^th generation immunoassay capable of detecting HIV-1 and HIV-2 antibodies and HIV-1 p24 antigen (called an antigen/antibody combination assay).A confirmed second positive HIV antibody test is diagnostic.

Children <18 months: A specific virologic test is necessary; HIV antibody testing in this age group may be misleading due to placental transfer of maternal HIV antibody, which can persist in the infant up to 18 months of age, even if the infant is not HIV-infected.

Diagnosis of perinatally acquired HIV in an infant: a specific virologic test should be performed at 14-21 days, 1-2 months, and 4-6 months of age; if all of these tests are negative, the infant does not have HIV infection. Regarding testing at 1-2 months, HIV exposed infants receiving prophylaxis should be tested 2-4 weeks after cessation of ART for prophylaxis. This means those on 4 weeks of prophylaxis should be tested at 6 weeks of age and those on 6 weeks of prophylaxis should be tested at 8 weeks of age.If any one of these tests is positive, a repeat virologic test on a second blood sample should be obtained as soon as the first result is available to confirm the diagnosis. The sensitivity of the HIV DNA PCR in perinatally acquired HIV is 96-98% by one month of age and almost 100% at 3 months of age for HIV subtype B (the primary subtype in the USA).DNA PCR may not be sensitive for refugees from Africa or Asia where non-subtype B HIV predominates.

Clinical clues which warrant evaluation for HIV

Children who present with unusual or recurrent infections indicative of immune dysfunction should be evaluated for HIV infection; for example, severe or prolonged varicella, recurrent or disseminated varicella zoster, frequent or extensive episodes of herpes simplex labialis, oral thrush over 1 year of age, prolonged diarrhea contributing to weight loss, recurrent fevers, or any opportunistic infection. In addition, any combination of poor growth, chronic lymphadenopathy, chronic or recurrent infections or developmental delay should prompt testing for HIV infection, in particular if the mother’s HIV status is unknown.

Adolescents who present with symptoms of acute retroviral syndrome should have an HIV antibody test, and if negative, a virologic test should be performed, as HIV antibody may not be detectable for 3-12 weeks after infection. Adolescents who present for testing immediately after an unprotected sexual encounter should be tested for HIV antibody to establish prior infection, and if negative, retested 3 months later. Post-exposure prophylaxis therapy should be considered following sexual assault or unprotected sex with a known HIV-infected person.

If you are able to confirm the patient has HIV, what treatment should be initiated?

Because HIV disease may progress rapidly in infants <12 months of age, antiretroviral therapy (ART) should be initiated in all infants in this age group, optimally before 12 weeks of age. Earlier initiation of ART for adults and adolescents prolongs survival and decreases morbidity. Thus for all age groups, ART should be started regardless of clinical staging or CD4 count. However, the urgency to start treatment varies with age, symptoms, CD4+T-lymphocyte count/percentage and the HIV RNA level in the blood (measured in copies/ml)(Table IV and Table V).

Table V:

The patient and/or caregiver should receive education regarding the importance of ARV adherence prior to initiation of therapy, as poor or inconsistent adherence will lead to selection of HIV drug resistance mutations.

There are >20 FDA-approved antiretroviral drugs (ARVs) for treatment of HIV disease (Table VI). A combination of three to four ARVs (combination antiretroviral therapy or cART) is recommended for initial and long term therapy; this typically consists of 2 nucleoside reverse transcriptase inhibitors (NRTIs) and either a non-nucleoside reverse transcriptase inhibitor (NNRTI), a protease inhibitor (PI) or integrase strand transfer inhibitor (INSTI). Most PI’s require pharmacologic “boosting” with ritonavir, a PI which lengthens the half-life of other PI’s by decreasing clearance through inhibition of the cytochrome P450 3A4 enzyme.

Table VI.

Considerations for selecting specific agents include potency, incidence and type of specific short- and long-term toxicities, dosing frequency (once versus twice daily), pill or liquid burden, potential for drug interactions and tolerability issues. ARV drug-resistance testing (genotype or phenotype tests, available through reference laboratories) should be performed prior to initiation of therapy.

Experts in treatment of Pediatric or Adolescent HIV should be consulted before selecting an ARV regimen. Guidelines for selecting an appropriate regimen developed by the Department of Health and Human Services’ Panel on Antiretroviral Therapy and Medical Management of HIV-infected Children are available at https://aidsinfo.nih.gov/guidelines/html/2/pediatric-arv-guidelines/0.

What are the adverse effects associated with treatment?

Nucleoside reverse transcription inhibitors (NRTIs): this class of ARVs is generally well tolerated but may have toxicity with long term use; i.e. the thymidine analogues (stavudine>didanosine>zidovudine) have been associated with mitochondrial toxicity such as lactic acidosis, and lipoatrophy.

Zidovudine is associated with macrocytic anemia or neutropenia in up to one third of individuals. Other common side effects include dizziness, fatigue, weakness, and muscle pain. Abacavir is associated with a rare (<5%), but life-threatening, hypersensitivity reaction; the HLA B*5701 gene assay can be used to identify individuals at higher risk for this reaction, but this test is most predictive for Caucasians and less so for other racial groups.

Tenofovir has been associated with reduced bone mineralization in adults. It has more recently been approved for use down to 2 years of age; if used, bone mineralization surveillance should be considered. Furthermore, tenofovir has been associated with a modest decline in glomerular clearance rate and subclinical tubular dysfunction in adults, so renal function should be monitored with this drug.

Non-nucleoside reverse transcription inhibitors (NNRTI’s): this class of ARVs may cause a diffuse maculo-papular rash in up to 30% of patients. It often resolves despite ongoing drug exposure, however, the drug should be discontinued if there is any mucous membrane involvement or disturbances of liver or renal function. Nevirapine has been associated with reversible liver toxicity but rare cases of liver failure and death have been reported. Efavirenz has been associated with sleep disturbance, dizziness and rarely, psychiatric symptoms, which resolve when the drug is discontinued; in addition, it has been found to be teratogenic in nonhuman primates, therefore effective contraception methods should be required when used in adolescent females. Hypersensitivity reactions including rash are infrequently seen with etravirine.

Protease Inhibitors (PIs): This class of drugs, in general, has the lowest tolerability, and has been most associated with gastrointestinal upset (diarrhea and/or nausea and vomiting); other toxicities may include liver enzyme elevation, serum lipid elevation (especially triglycerides) and central fat accumulation (lipodystrophy, see Complications, below.)

Integrase Inhibitors (INSTI): This class of drug are still undergoing evaluation in children. Dolutegravir has been licensed for children over 12 years or 40 kg. The safety profile of this class is favorable with only minor side effects in adults and adolescents and few drug-drug interactions.

Other newer classes of antiretroviral drugs, such as entry inhibitors, are still undergoing evaluation in children.

Many ARVs, especially the PIs and NNRTIs, have multiple drug-drug interactions with ARVs and other classes of drugs. A pharmacist experienced in the use of ARVs should be consulted to investigate possible interactions before prescribing these drugs.

What are the possible outcomes of this disease?

Mortality from HIV/AIDS has been reduced by >90% by the introduction of cART, and HIV/AIDS, with appropriate treatment, can now be considered a chronic disease. However, antiretroviral therapy is life-long and requires pristine adherence to antiretroviral therapy for viral control and immunologic reconstitution; the day-in-day-out requirement of cART therapy remains a substantial challenge for many caregivers of young children, who may resist taking unpalatable liquid formulations of ARVs, as well as for older HIV-infected children and adolescents. Nonadherence increases the likelihood of selection of ARV resistance mutations, which may lead to loss of virologic suppression and, ultimately, disease progression and death.

Important clinical presentations to recognize

The most common life-threatening presentation of HIV is Pneumocystis jiroveci (formerly P. carinii) pneumonia (PCP). The hallmark features include fever, tachypnea and hypoxemia with rapid progression to respiratory failure. Pulmonary examination may reveal crackles or rhonchi but is normal in many patients despite profound hypoxemia. Chest x-ray shows diffuse interstitial or alveolar infiltrates. Diagnosis is made by demonstrating the organism in broncho-alveolar lavage by staining techniques (e.g., methenamine silver) or by direct immunofluorescence using monoclonal antibodies. PCP can be prevented with antibiotic prophylaxis. Trimethoprim/sulfamethoxazole (TMP/SMX), given when the CD4 count falls below 15% (young children) or <200 cells/mm3 (> 6 years of age), is used most commonly. Other options include dapsone, atovaquone, or aerosolized pentamidine.PCP primarily occurs in infants or adolescents with previously undiagnosed HIV or HIV-infected patients not adherent to prophylaxis regimens.

A chronic lower respiratory tract process unique to children with HIV is lymphocytic interstitial pneumonitis (LIP); some evidence suggests this may be the result of a poorly controlled lymphoproliferative response to a primary Epstein Barr virus infection. LIP presents with clubbing of the fingers, insidious onset of tachypnea and hypoxemia, with a typical reticulonodular infiltrate +/- hilar lymphadenopathy on chest x-ray; these radiographic findings may be indistinguishable from PCP, except that they significantly predate the onset of symptoms. Once responsible for ~30% of AIDS diagnoses in children, LIP has become rare in the era of cART.

Painless parotid enlargement (unilateral or bilateral) is another finding more common in children than adults and is often seen in children with LIP.

Complications of HIV disease and its treatment

Lipodystrophy, or abnormal body fat distribution, historically occurred in 20-60% of individuals taking ARVs but has become less common with newer ART regimens. This presents with either lipoatrophy of the face, extremities, and/or buttocks, or central fat accumulation in the viscera and trunk, breasts or cervicodorsal fat pad (buffalo hump), or both. The pathophysiology of this process is not well-defined and is likely due to a combination of mitochondrial toxicity, genetic predisposition, and virus- and drug-mediated effects on adipose tissue.

Insulin levels are up to 40% higher in HIV-infected children than HIV-negative controls, and up to 15% of patients have impaired glucose tolerance; the latter may correlate with longer duration of ART and higher use of PIs. These youth require follow-up for development of diabetes.

Cardiovascular disease (CVD) occurs at a higher rate in HIV-infected adults than in the general population. Increased carotid-intima-media thickness has been found in perinatally infected youth compared to healthy age-matched controls. When compared with controls, a cohort of 240 HIV-infected children aged 7-24 years was found to have more dyslipidemia (significantly lower high-density lipoprotein cholesterol (HDL) levels and higher mean total low-density lipoprotein cholesterol (LDL) in those taking protease inhibitors). The degree to which children and adolescents with HIV will suffer from accelerated CVD is an area of active research.

Adults with HIV have a higher risk of bone fracture than healthy controls. The mechanism for lower bone mineral density (BMD) in HIV disease is not fully elucidated, but likely includes a combination ofhost factors, disease status, chronic inflammation, low calcium intake and relative vitamin D deficiency, as well as effects of multiple different antiretroviral drugs. Longitudinal studies have demonstrated a significant decrease in BMD within the first 6 months of initiation of ART which then stabilizes, suggesting a possible role of immune reconstitution in bone loss.

Chronic kidney disease, or HIV-associated nephropathy, is most common among African-American HIV-infected individuals, and presents with proteinuria, +/- elevated serum creatinine, edema or hypertension. The largest series of HIV+ children followed prospectively for renal toxicity (n= 2102) reported a 22% incidence of at least one persistent kidney laboratory abnormality, with an elevated serum creatinine in 15% and proteinuria in 8%.

In adults, HIV is associated with a higher incidence of neoplasms than in the general population, but the association is not as strong in pediatric HIV disease. The incidence of AIDS-defining malignancies has decreased since the introduction of highly active ART. However, the incidence of non-AIDS defining malignancies is increasing and contributes to mortality despite cART; this increase may be related to prolonged survival, co-infections (HPV, hepatitis B and C, EBV) and lifestyle choices (smoking, sun exposure, sexual habits, etc.). As adults, children and adolescents with HIV infection will need ongoing surveillance for neoplasms, despite adequate immune reconstitution with ART.

What causes this disease and how frequent is it?

Infants acquire HIV perinatally from an HIV-infected mother, either during gestation (in utero), at the time of delivery (peripartum) or postpartum during breastfeeding. Treatment of HIV+ mothers and their infants with ARVs can successfully prevent mother to child transmission (see Prevention, below) and it is now estimated that <100 HIV-infected infants are born in the US each year, despite more than an estimated 9000 deliveries to HIV+ mothers. However, in resource-poor countries, where 99% of the >2 million HIV infected children in the world reside, limited availability of ARVs and coordinated pre- and perinatal care has remained a challenge, fueling the source of ongoing pediatric HIV infection in these regions.

The adolescent population acquires HIV through high-risk sexual activity (i.e. sex with a partner known to have or be at high risk for HIV infection including men who have sex with men [MSM]) and less frequently, through injection of infected blood through shared needles during IV drug use. The Centers for Disease Control and Prevention (CDC) estimated that youth aged 13 to 24 accounted for 22% of all new HIV infections diagnosed in 2014. Most of these (80%) occurred among young gay and bisexual males. Young black/African American (55%) and Hispanic/Latino (23%) gay and bisexual males are especially affected.

CDC estimated that only 15%of new HIV diagnoses among youth 13-24 years of age in 2014 were in females. In this group, HIV is usually acquired through heterosexual sex, often with older partners. In both sexes, injection drug use, other recreational drugs and alcohol are associated with social disinhibition and increased risk behaviors that predispose to infection. The CDC has estimated that the majority of HIV+ adolescents are unaware of their diagnosis.

In the United States, HIV is over-represented in minority racial/ethnic populations. For example, in 2008, black/African Americans comprised only 17% of the US population of adolescents 13-19 years of age but 75% of HIV infected youth. Perinatally infected children display similar racial disparities.

With the decreasing rate of new infections among infants born to mothers with HIV infection and the rise in adolescent infections, the proportion of HIV+ patients in Pediatrics is shifting from infants/children to adolescents with behaviorally acquired disease.

How do these pathogens/genes/exposures cause this disease?

After a single “founder” virus or HIV infected cell gains access to thebody,mostfrequentlythrougha mucosal surface and less often, directly into the circulation, it intensively replicates and disseminates to lymphoid tissues. This results in a peak plasma viral load of up to 10 million HIV RNA copies/ml and significant CD4+ T-cell depletion. During this time chronic persistent viral reservoirs are established in lymphoid tissues and long-lived resting CD4+ T cells, which contribute to an indefinite ongoing source of newly infected cells.

Perinatally infected infants typically maintain viral loads between 200,000 to 1 million copies/ml for up to 2 years. In contrast, most adolescents and adults have a spontaneous decline in viral load to a lower set point within several weeks as the host immune response, albeit inadequate for virus control or eradication, is generated. A chronic, usually asymptomatic phase of 1->10 years of sustained viral replication and immune activation ensues, which, in the absence of therapy, eventually leads to CD4+ T cell depletion and advanced immune deficiency.

Are additional laboratory studies available; even some that are not widely available?

Hypergammaglobulinemia is a consistent laboratory finding among HIV-infected children, due to polyclonal activation of B cells with HIV infection. Ironically, specific antibody formation is typically impaired.

How can HIV be prevented?

It is now standard of care to test all women for HIV infection during pregnancy. Positive women should be treated with cART early in gestation and intravenous zidovudine during labor and delivery to prevent transmission; infants are then treated with oral zidovudine for the first 6 weeks of life. This regimen has reduced transmission from a rate of ~25% in untreated mother/infant pairs to <1.5%. Women in labor whose HIV status is unknown should have rapid antibody testing performed so that IV zidovudine therapy can be instituted in the mother and the infant can be appropriately prophylaxed. Women in the US are also advised not to breastfeed, to eliminate this route of exposure.

Prevention in adolescents should focus on safer sexual practices and avoidance of recreational drug use. The CDC has estimated that >50% of HIV+ adolescents are unaware of their diagnosis, many of whom engage in unprotected sex. Condoms, when used consistently and correctly, are highly effective in preventing transmission, with efficacy estimated to be >90%.

Receptive anal intercourse has the highest risk for transmission. Studies in sub-Saharan Africa have demonstrated that male circumcision reduces the risk of acquiring HIV from heterosexual intercourse by over 60%. A double-blind, randomized controlled trial of vaginal 1% tenofovir gel before intercourse showed a 39% overall reduction in incident cases of HIV in women in South Africa.

Pre-exposure prophylaxis (PreP) using a daily dose of a single combination pill of tenofovir and emtricitabine has been associated with a reduction in transmission of at least 44% in adult MSM and 63% in heterosexual partners. Intravenous drug use involving shared needles has the highest risk for HIV transmission but use of other recreational drugs is more frequent and may reduce inhibition and promote unprotected sex.

In 2006, the CDC recommended that “opt-out”, voluntary HIV antibody testing should become a part of routine clinical care for all patients aged 13-64 years, that is, informing individuals that HIV testing will be performed unless expressly declined. This initiative aims to promote early diagnosis and treatment. In addition, because it is estimated that sexual transmission is 3.5 times higher among those who are unaware of their diagnosis, routine testing should contribute to adoption of better preventive practices for HIV+ individuals.

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