Infant CD4 C868T polymorphism is associated with increased human immunodeficiency virus (HIV-1) acquisition.

The C868T single nucleotide polymorphism (SNP) in the CD4 receptor encodes an amino acid change that could alter its structure and influence human immunodeficiency virus (HIV-1) infection risk. HIV-1-infected pregnant women in Nairobi were followed with their infants for 1 year postpartum. Among 131 infants, those with the 868T allele were more likely than wild-type infants to acquire HIV-1 overall [hazard ratio (HR) = 1.92, 95% confidence interval (CI) 1.05, 3.50, P = 0.03; adjusted HR = 2.03, 95% CI 1.03, 3.98, P = 0.04], after adjusting for maternal viral load. This SNP (an allele frequency of approximately 15% in our cohort) was associated with increased susceptibility to mother-to-child HIV-1 transmission, consistent with a previous study on this polymorphism among Nairobi sex workers.

Infants with late breast milk acquisition of HIV-1 generate interferon-gamma responses more rapidly than infants with early peripartum acquisition.

Infants infected with HIV-1 after the first month of life have a lower viral set-point and slower disease progression than infants infected before 1 month. We investigated the kinetics of HIV-1-specific CD8(+) T lymphocyte secretion of interferon (IFN)-gamma in infants infected before 1 month of life compared with those infected between months 1 and 12 (late infection). HIV-1 infection was assessed at birth and at months 1, 3, 6, 9 and 12 and timing of infection was determined by HIV-1 gag DNA from dried blood spots and verified by plasma HIV-1 RNA levels. HIV-1 peptide-specific IFN-gamma responses were measured by enzyme-linked immunospot at months 1, 3, 6, 9 and 12. Timing of development of IFN-gamma responses was compared using the log-rank test and Kaplan-Meier survival curves. Infants infected late developed HIV-1-specific CD8(+) T cell responses 2.8 months sooner than infants infected peripartum: 2.3 versus 5.1 months after HIV-1 infection (n = 52, P = 0.04). Late-infected infants had more focused epitope recognition than early-infected infants (median 1 versus 2 peptides, P = 0.03); however, there were no differences in the strength of IFN-gamma responses. In infants infected with HIV-1 after the first month of life, emergence of HIV-1-specific CD8(+) IFN-gamma responses is coincident with the decline in viral load, nearly identical to what is observed in adults and more rapid than in early-infected infants.

Salivary human immunodeficiency virus (HIV)-1-specific immunoglobulin A in HIV-1-exposed infants in Kenya.

Humoral immunity, and specifically immunoglobulin A (IgA) that is directed against human immunodeficiency virus (HIV)-1, may contribute to protection against HIV-1 acquisition at mucosal surfaces. HIV-1-specific IgA has been detected in genital tract secretions of HIV-1-uninfected commercial sex workers with HIV-1 exposure, and may be produced in parotid saliva by infants exposed orally to HIV-1 during delivery and breastfeeding. To explore this hypothesis, we collected saliva from 145 infants aged < or = 6 months enrolled in a perinatal HIV-1 transmission study in Nairobi and from 55 control infants without HIV-1 exposure who were born to HIV-1-seronegative mothers. Among the 145 infants, 115 (79%) remained uninfected during the 12-month study period and 30 (21%) became HIV-1-infected during follow-up. Nine (8%) of the 115 HIV-1-exposed, uninfected infants had detectable levels of HIV-1 gp160-specific IgA compared with four (13%) of 30 infected infants and none of 55 control infants (P = 0.47 and P = 0.03 respectively). Among the nine HIV-1-exposed, uninfected infants with positive assays, median age was 1 month and none acquired HIV-1 during follow-up. We conclude that HIV-1-specific salivary IgA responses may be generated by very young infants exposed perinatally to maternal HIV-1. Mucosal responses would be an appropriate target for paediatric vaccines against breast milk HIV-1 transmission.

Contextualising the paediatric HIV epidemic: a review.

OBJECTIVE: To draw attention to the sub-optimal care that HIV-infected children are receiving in Africa. DATA SOURCES: Relevant published literature. DATA SYNTHESIS: Sub-optimal response to paediatric HIV infection has aggravated the negative impact that the epidemic has had on child health in Africa. Recently the African Network for the Care of Children Affected by HIV/AIDS (ANNECA) released an advocacy statement that called for the optimisation of prevention, diagnosis, treatment and care for children affected by the AIDS pandemic. Effective prevention strategies if comprehensively implemented, could prevent more than 500 000 paediatric infections per annum at current antenatal HIV prevalence rates. Improved care that includes universal utilisation of early diagnostic testing systems, cotrimoxazole prophylaxis, nutritional support and the timely introduction of antiretroviral therapy could improve the quality of life and lifespan of most infected children. CONCLUSION: Political leaders, public health officials and fellow child health professionals are urged to redouble their efforts to reverse the magnitude of the paediatric epidemic in Africa.

Predictors of mortality in HIV-1 exposed uninfected post-neonatal infants at the Kenyatta National Hospital, Nairobi.

OBJECTIVES: To identify potential predictors of mortality, to determine mortality rate and to identify prevalent causes of death in a cohort of HIV-1 exposed uninfected infants. DESIGN: Prospective cohort study. SETTING: Kenyatta National Hospital, Nairobi, Kenya. SUBJECTS: Three hundred and fifty one HIV-1 exposed uninfected post-neonatal infants who survived to one year of age. RESULTS: Sixteen infants died (post-neonatal mortality rate of 47/1000 live births), 14 (88%) before six months of age. The most frequently identified medical conditions at death included bronchopneumonia, diarrhoea and failure to thrive. In multivariate analysis, prematurity (RR=10.5, 95%CI 3.8-29.1, p<0.001), teenage motherhood (RR=3.6, Cl 1.0-13.2, p=0.05) and symptomatic maternal HIV-1 disease (RR=2.7, CI 0.9-7.7, p=0.06) were associated with infant mortality. CONCLUSION: Prematurity, teenage motherhood and symptomatic HIV-1 maternal disease were important predictors for post-neonatal mortality in this cohort of HIV-1 exposed uninfected infants. These factors should be considered in monitoring and follow up in prevention of mother-to-child HIV-1 transmission (PMTCT) programs.

Evaluation of a proposed clinical case definition of paediatric acquired immune deficiency syndrome.

OBJECTIVE: To evaluate the proposed criteria against the laboratory parameters and to identify the clinical features with the highest predictive value in the diagnosis of paediatric AIDS. DESIGN: A cross sectional study. SETTING: Kenyatta National Hospital, Nairobi. RESULTS: More than twenty three per cent of the children studied were seropositive and 14% were diagnosed as having AIDS. Almost 70% of the children studied were below 24 months. AIDS was significantly associated with mouth lesions, both ulcers and oral candidiasis, skin lesions especially eczema and generalised pruritic dermatitis, prolonged cough, prolonged fever and generalised lymphadenopathy. The WHO criteria had a sensitivity of 60%, a specificity of 94%, positive predictive value of 60%, and negative predictive value of 94%. The Nairobi diagnostic criteria had a sensitivity of 80%, a specificity of 79%, a positive predictive value of 38% and a negative predictive value of 96%. CONCLUSION: The Nairobi Diagnostic Criteria are superior to the WHO criteria as a screening test due to their higher sensitivity, 80% against 60% for WHO.

Morbidity and mortality in breastfed and formula-fed infants of HIV-1-infected women: A randomized clinical trial.

CONTEXT: Breastfeeding among women infected with human immunodeficiency virus type 1 (HIV-1) is associated with substantial risk of HIV-1 transmission, but little is known about the morbidity risks associated with formula feeding in infants of HIV-1-infected women in resource-poor settings. OBJECTIVE: To compare morbidity, nutritional status, mortality adjusted for HIV-1 status, and cause of death among formula-fed and breastfed infants of HIV-1-infected women. DESIGN: Randomized clinical trial conducted between 1992 and 1998. SETTING: Four antenatal clinics in Nairobi, Kenya. PARTICIPANTS: Of 401 live-born, singleton, or first-born twin infants of randomized HIV-1-seropositive mothers, 371 were included in the analysis of morbidity and mortality. INTERVENTIONS: Mothers were randomly assigned either to use formula (n = 186) or to breastfeed (n = 185) their infants. MAIN OUTCOME MEASURES: Mortality rates, adjusted for HIV-1 infection status; morbidity; and nutritional status during the first 2 years of life. RESULTS: Two-year estimated mortality rates among infants were similar in the formula-feeding and breastfeeding arms (20.0% vs 24.4%; hazard ratio [HR], 0.8; 95% confidence interval [CI], 0.5-1.3), even after adjusting for HIV-1 infection status (HR, 1.1; 95% CI, 0.7-1.7). Infection with HIV-1 was associated with a 9.0-fold increased mortality risk (95% CI, 5.3-15.3). The incidence of diarrhea during the 2 years of follow-up was similar in formula and breastfeeding arms (155 vs 149 per 100 person-years, respectively). The incidence of pneumonia was identical in the 2 groups (62 per 100 person-years), and there were no significant differences in incidence of other recorded illnesses. Infants in the breastfeeding arm tended to have better nutritional status, significantly so during the first 6 months of life. CONCLUSIONS: In this randomized clinical trial, infants assigned to be formula fed or breastfed had similar mortality rates and incidence of diarrhea and pneumonia during the first 2 years of life. However, HIV-1-free survival at 2 years was significantly higher in the formula arm. With appropriate education and access to clean water, formula feeding can be a safe alternative to breastfeeding for infants of HIV-1-infected mothers in a resource-poor setting.

Timing of breast milk HIV-1 transmission: a meta-analysis.

OBJECTIVE: To define the frequency and timing of breast milk transmission of HIV-1. DESIGN: Meta-analysis of data abstracted from published literature. SUBJECTS: Participants in prospective cohort studies of MTCT of HIV-1. Cohorts were separated on the basis of breast feeding duration. INTERVENTIONS: None. MAIN OUTCOME MEASURES: HIV-1 transmission rates. RESULTS: Two thousand three hundred and seventy five HIV-1 infected women and their infants, 499 of whom breast fed, the estimated risk of breast milk HIV-1 transmission was 16% (95% CI: 9, 22%). Among breastfeeding infants, forty seven per cent of HIV-1 infections were attributable to breast feeding. Breast milk transmission risk was 21% (95% CI: 10, 33%) in cohorts with mean/median duration of breast feeding > or = 3 months and 13% (95% CI: 4, 21%) in cohorts with median duration of breast feeding < 2 months. In a separate analysis of 702 infants with prolonged duration of breast feeding, the risk of late postnatal transmission (infection occurring later than three to six months of age) was four per cent (95% CI 2, 5%). CONCLUSIONS: This analysis suggests that breast milk transmission of HIV-1 is substantial and continues throughout the postnatal period. Early cessation of breast feeding at six months would avert some but not most infant HIV-1 infections due to breast feeding. While recently published studies showing some effectiveness of antiretrovirals early during the breast feeding period are encouraging, prevention of breast milk HIV-1 transmission needs to remain a high research priority.

Effect of breastfeeding on mortality among HIV-1 infected women: a randomised trial.

BACKGROUND: We have completed a randomised clinical trial of breastfeeding and formula feeding to identify the frequency of breastmilk transmission of HIV-1 to infants. However, we also analysed data from this trial to examine the effect of breastfeeding on maternal death rates during 2 years after delivery. We report our findings from this secondary analysis. METHODS: Pregnant women attending four Nairobi city council clinics were offered HIVtests. At about 32 weeks' gestation, 425 HIV-1 seropositive women were randomly allocated to either breastfeed or formula feed their infants. After delivery, mother-infant pairs were followed up monthly during the first year and quarterly during the second year until death, or 2 years after delivery, or end of study. FINDINGS: Mortality among mothers was higher in the breastfeeding group than in the formula group (18 vs 6 deaths, log rank test, p=0.009). The cumulative probability of maternal death at 24 months after delivery was 10.5% in the breastfeeding group and 3.8% in the formula group (p=0.02). The relative risk of death for breastfeeding mothers versus formula feeding mothers was 3.2 (95% CI 1.3-8.1, p=0.01). The attributable risk of maternal death due to breastfeeding was 69%. There was an association between maternal death and subsequent infant death, even after infant HIV-1 infection status was controlled for (relative risk 7.9, 95% CI 3.3-18.6, p<0.001). INTERPRETATION: Our findings suggest that breastfeeding by HIV-1 infected women might result in adverse outcomes for both mother and infant.

CCR5 promoter polymorphisms in a Kenyan perinatal human immunodeficiency virus type 1 cohort: association with increased 2-year maternal mortality.

The CCR5 chemokine receptor acts as a coreceptor with CD4 to permit infection by primary macrophage-tropic human immunodeficiency virus type 1 (HIV-1) strains. The CCR5Delta32 mutation, which is associated with resistance to infection in homozygous individuals and delayed disease progression in heterozygous individuals, is rare in Africa, where the HIV-1 epidemic is growing rapidly. Several polymorphisms in the promoter region of CCR5 have been identified, the clinical and functional relevance of which remain poorly defined. We evaluated the effect of 4 CCR5 promoter mutations on systemic and mucosal HIV-1 replication, disease progression, and perinatal transmission in a cohort of 276 HIV-1-seropositive women in Nairobi, Kenya. Mutations at positions 59353, 59402, and 59029 were not associated with effects on mortality, virus load, genital shedding, or transmission in this cohort. However, women with the 59356 C/T genotype had a 3.1-fold increased risk of death during the 2-year follow-up period (95% confidence interval [CI], 1.0-9.5) and a significant increase in vaginal shedding of HIV-1-infected cells (odds ratio, 2.1; 95% CI, 1.0-4.3), compared with women with the 59356 C/C genotype.

Comparison of techniques for HIV-1 RNA detection and quantitation in cervicovaginal secretions.

PRINCIPLES: HIV-1 in female genital secretions has been measured using swabs, Sno Strips (Akorn, Inc., Buffalo Grove, IL), and cervicovaginal lavage (CVL), but little is known regarding the comparability of these collection techniques. METHODS: We compared HIV-1 RNA detection and quantity in specimens obtained from HIV-1-seropositive women in Kenya using three sample collection techniques and three storage techniques and evaluated reproducibility in samples collected 5 days apart. Specimens were stored in no medium, freezing medium, or TRI Reagent (Molecular Research Center, Cincinnati, OH) for 2 to 15 months. RESULTS: HIV-1 RNA assays were conducted on 640 specimens from 20 antiretroviral naive women. Storage in TRI Reagent significantly enhanced detection of genital HIV-1 and yielded significantly higher mean log10 RNA levels than specimens collected in either no or freezing medium. The prevalence of HIV-1 RNA detection in TRI Reagent ranged from 50% to 80% depending on collection method and was highest in cervical swabs. Mean log10 HIV-1 RNA levels were 3.1 log10 copies/cervical swab, 2.6 log10 copies/cervical Sno Strip, 2.5 log10 copies/vaginal swab, 2.4 log10 copies/vaginal Sno Strip, 2.9 log10 copies/ml for cervicovaginal lavage (CVL) cell pellet, and 2.1 log10 copies/ml in CVL supernatant. Comparing specimens from days 1 and 6, there was significant concordance of HIV-1 RNA detection and correlation of HIV-1 RNA levels for cervical swabs, vaginal swabs, vaginal Sno Strips, and CVL cell pellets (kappa, 0.5-0.9; r, 0.5-0.9), but not for cervical Sno Strips or CVL supernatants. CONCLUSIONS: Cervical or vaginal swab, vaginal Sno Strip, and CVL collection led to reproducible measurement of genital HIV-1 RNA, despite storage for several months and international transport. Collection using swabs was simpler than Sno Strips or cervicovaginal lavage, and yielded the highest prevalence of HIV-1 RNA detection and reproducibility.

Correlates of mother-to-child human immunodeficiency virus type 1 (HIV-1) transmission: association with maternal plasma HIV-1 RNA load, genital HIV-1 DNA shedding, and breast infections.

To determine the effects of plasma, genital, and breast milk human immunodeficiency virus type 1 (HIV-1) and breast infections on perinatal HIV-1 transmission, a nested case-control study was conducted within a randomized clinical trial of breast-feeding and formula feeding among HIV-1-seropositive mothers in Nairobi, Kenya. In analyses comparing 92 infected infants with 187 infants who were uninfected at 2 years, maternal viral RNA levels >43,000 copies/mL (cohort median) were associated with a 4-fold increase in risk of transmission (95% confidence interval [CI], 2.2-7.2). Maternal cervical HIV-1 DNA (odds ratio [OR], 2.4; 95% CI, 1.3-4.4), vaginal HIV-1 DNA (OR, 2.3; 95% CI, 1.1-4.7), and cervical or vaginal ulcers (OR, 2.7; 95% CI, 1.2-5.8) were significantly associated with infant infection, independent of plasma virus load. Breast-feeding (OR, 1.7; 95% CI, 1.0-2.9) and mastitis (relative risk [RR], 3.9; 95% CI, 1.2-12.7) were associated with increased transmission overall, and mastitis (RR, 21.8; 95% CI, 2.3-211.0) and breast abscess (RR, 51.6; 95% CI, 4.7-571.0) were associated with late transmission (occurring >2 months postpartum). Use of methods that decrease infant exposure to HIV-1 in maternal genital secretions or breast milk may enhance currently recommended perinatal HIV-1 interventions.

Maternal SDF1 3'A polymorphism is associated with increased perinatal human immunodeficiency virus type 1 transmission.

Genetic polymorphisms in chemokine and chemokine receptor genes influence susceptibility to human immunodeficiency virus type 1 (HIV-1) infection and disease progression, but little is known regarding the association between these allelic variations and the ability of the host to transmit virus. In this study, we show that the maternal heterozygous SDF1 genotype (SDF1 3'A/wt) is associated with perinatal transmission of HIV-1 (risk ratio [RR], 1.8; 95% confidence interval [CI], 1.0 to 3.3) and particularly postnatal breastmilk transmission (RR, 3.1; 95% CI, 1.1 to 8.6). In contrast, the infant SDF1 genotype had no effect on mother-to-infant transmission. These data suggest that SDF1, which is a ligand for the T-tropic HIV-1 coreceptor CXCR4, may affect the ability of a mother to transmit the virus to her infant. This suggests that a genetic polymorphism in a gene encoding a chemokine receptor ligand may be associated with increased infectivity of the index case and highlights the importance of considering transmission as well as clinical outcome in designing chemokine-based therapies for HIV-1.

Effect of breastfeeding and formula feeding on transmission of HIV-1: a randomized clinical trial.

CONTEXT: Transmission of human immunodeficiency virus type 1 (HIV-1) is known to occur through breastfeeding, but the magnitude of risk has not been precisely defined. Whether breast milk HIV-1 transmission risk exceeds the potential risk of formula-associated diarrheal mortality in developing countries is unknown. OBJECTIVES: To determine the frequency of breast milk transmission of HIV-1 and to compare mortality rates and HIV-1-free survival in breastfed and formula-fed infants. DESIGN AND SETTING: Randomized clinical trial conducted from November 1992 to July 1998 in antenatal clinics in Nairobi, Kenya, with a median follow-up period of 24 months. PARTICIPANTS: Of 425 HIV-1-seropositive, antiretroviral-naive pregnant women enrolled, 401 mother-infant pairs were included in the analysis of trial end points. INTERVENTIONS: Mother-infant pairs were randomized to breastfeeding (n = 212) vs formula feeding arms (n = 213). MAIN OUTCOME MEASURES: Infant HIV-1 infection and death during the first 2 years of life, compared between the 2 intervention groups. RESULTS: Compliance with the assigned feeding modality was 96% in the breastfeeding arm and 70% in the formula arm (P<.001). Median duration of breastfeeding was 17 months. Of the 401 infants included in the analysis, 94% were followed up to HIV-1 infection or mortality end points: 83% for the HIV-1 infection end point and 93% to the mortality end point. The cumulative probability of HIV-1 infection at 24 months was 36.7% (95% confidence interval [CI], 29.4%-44.0%) in the breastfeeding arm and 20.5% (95% CI, 14.0%-27.0%) in the formula arm (P = .001). The estimated rate of breast milk transmission was 16.2% (95% CI, 6.5%-25.9%). Forty-four percent of HIV-1 infection in the breastfeeding arm was attributable to breast milk. Most breast milk transmission occurred early, with 75% of the risk difference between the 2 arms occurring by 6 months, although transmission continued throughout the duration of exposure. The 2-year mortality rates in both arms were similar (breastfeeding arm, 24.4% [95% CI, 18.2%-30.7%] vs formula feeding arm, 20.0% [95% CI, 14.4%-25.6%]; P = .30). The rate of HIV-1-free survival at 2 years was significantly lower in the breastfeeding arm than in the formula feeding arm (58.0% vs 70.0%, respectively; P = .02). CONCLUSIONS: The frequency of breast milk transmission of HIV-1 was 16.2% in this randomized clinical trial, and the majority of infections occurred early during breastfeeding. The use of breast milk substitutes prevented 44% of infant infections and was associated with significantly improved HIV-1-free survival.

Subtypes of human immunodeficiency virus type 1 and disease stage among women in Nairobi, Kenya.

In sub-Saharan Africa, where the effects of human immunodeficiency virus type 1 (HIV-1) have been most devastating, there are multiple subtypes of this virus. The distribution of different subtypes within African populations is generally not linked to particular risk behaviors. Thus, Africa is an ideal setting in which to examine the diversity and mixing of viruses from different subtypes on a population basis. In this setting, it is also possible to address whether infection with a particular subtype is associated with differences in disease stage. To address these questions, we analyzed the HIV-1 subtype, plasma viral loads, and CD4 lymphocyte levels in 320 women from Nairobi, Kenya. Subtype was determined by a combination of heteroduplex mobility assays and sequence analyses of envelope genes, using geographically diverse subtype reference sequences as well as envelope sequences of known subtype from Kenya. The distribution of subtypes in this population was as follows: subtype A, 225 (70.3%); subtype D, 65 (20.5%); subtype C, 22 (6.9%); and subtype G, 1 (0.3%). Intersubtype recombinant envelope genes were detected in 2.2% of the sequences analyzed. Given that the sequences analyzed represented only a small fraction of the proviral genome, this suggests that intersubtype recombinant viral genomes may be very common in Kenya and in other parts of Africa where there are multiple subtypes. The plasma viral RNA levels were highest in women infected with subtype C virus, and women infected with subtype C virus had significantly lower CD4 lymphocyte levels than women infected with the other subtypes. Together, these data suggest that women in Kenya who are infected with subtype C viruses are at more advanced stages of immunosuppression than women infected with subtype A or D. There are at least two models to explain the data from this cross-sectional study; one is that infection with subtype C is associated with a more rapid disease progression, and the second is that subtype C represents an older epidemic in Kenya. Discriminating between these possibilities in a longitudinal study will be important for increasing our understanding of the role of specific subtypes in the transmission and pathogenesis of HIV-1.

Studies of human immunodeficiency virus type 1 mucosal viral shedding and transmission in Kenya.

If human immunodeficiency virus type 1 (HIV-1) vaccines are to be highly effective, it is essential to understand the virologic factors that contribute to HIV-1 transmission. It is likely that transmission is determined, in part, by the genotype or phenotype (or both) of infectious virus present in the index case, which in turn will influence the quantity of virus that may be exchanged during sexual contact. Transmission may also depend on the fitness of the virus for replication in the exposed individual, which may be influenced by whether a virus encounters a target cell that is susceptible to infection by that specific variant. Of interest, our data suggest that the complexity of the virus that is transmitted may be different in female and male sexual exposures.

Rapid method for screening dried blood samples on filter paper for human immunodeficiency virus type 1 DNA.

PCR is a highly sensitive method for the detection of human immunodeficiency virus type 1 (HIV-1) nucleic acids in blood mononuclear cells and plasma. However, blood separation techniques require extensive laboratory support systems and are difficult when a limited volume of blood is available, which is often the case for infants. The use of blood samples stored on filter paper has many advantages for the detection of perinatal HIV-1 infection, but current methods require extraction and purification of target DNA prior to PCR amplification. We report a highly sensitive and rapid method for the extraction and detection of HIV-1 DNA in infant blood samples stored on filter papers. Because this rapid protocol does not involve steps for the removal of potential inhibitors of the PCR, the highest sensitivity is achieved by testing the filter paper lysate in quadruplicate. Assays for HIV-1 DNA were done by using nested PCR techniques that amplify HIV-1 gag DNA from blood spot samples on filter paper and from corresponding viably frozen mononuclear cells separated from venous blood samples obtained from 111 infants born to HIV-1-seropositive mothers. PCR results with blood from filter papers showed 100% specificity (95% confidence internal [CI] 93.1 to 100%) and 96% (95% CI, 88.65 to 98.9%) and 88% (95% CI, 79.2 to 94.5%) sensitivity (for quadruplicate and duplicate tests, respectively) compared to PCR results with blood mononuclear cells. Moreover, this method could detect HIV-1 sequences of multiple subtypes.