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OBJECTIVES: Although the treatment of pregnant women and their infants with zidovudine (ZDV) has been remarkably effective in preventing the perinatal transmission of human HIV-1, many potentially preventable infections still occur. To examine whether the risk of perinatal infection is increased among women who carry ZDV-resistant HIV-1, the role of genotypic ZDV resistance in perinatal transmission was evaluated. METHODS: The reverse transcriptase (RT) region of clinical isolates from culture supernatants of 142 HIV-1-infected women enrolled in the Women and Infants Transmission Study (WITS), who had been treated with ZDV during pregnancy was sequenced. Results from genotypic sequencing were linked to demographic, laboratory, and obstetrical databases, and the magnitude of association of having consensus drug-resistant HIV-1 RT mutations with transmission was estimated. RESULTS: Twenty-five per cent (34/142) of maternal isolates had at least one ZDV-associated resistance mutation. A lower CD4 cell percentage and count (P= 0.0001) and higher plasma HIV-1 RNA (P=0.006) were associated with having any ZDV resistance mutation at delivery. Having any RT resistance mutation [odds ratio (OR): 5.16; 95% confidence interval (CI): 1.40, 18.97; P=0 0.01], duration of ruptured membranes [OR: 1.13 (1.02, 1.26) per 4 h duration; P= 0.02], and total lymphocyte count [OR: 1.06 (1.01, 1.10) per 50 cells higher level; P=0.009] were independently associated with transmission in multivariate analysis. CONCLUSION: Maternal ZDV resistant virus was predictive of transmission, independent of viral load, in these mothers with moderately advanced HIV-1 disease, many of whom had been treated with ZDV before pregnancy.
A cDNA clone containing the complete coding region of RNA2 of the newly described TPA56 isolate of pea early-browning virus (English serotype, PEBV-E) has been obtained. A plasmid (pFLA56) containing this clone together with the 5' and 3' non-coding regions of PEBV isolate SP5 (the type isolate of PEBV-E) and flanked by the CaMV 35S promoter and NOS terminator is infectious when co-inoculated onto plants with pCaN1, an infectious clone of PEBV SP5 RNA1. Virus containing RNA2 derived from the cDNA clone of the TPA56 isolate is transmitted by Trichodorus primitivus nematodes, whereas virus containing RNA2 from a clone of the SP5 isolate is not transmitted. Sequencing revealed 11 differences out of 3374 nucleotides between the transmissible TPA56 and non-transmissible SP5 clones. However, only three of the base changes affected the amino acid sequences of virus gene products. A single, conservative amino acid change was present in the virus coat protein. Two non-conservative changes occurred in the protein of molecular mass 29.6 kDa expressed from an open reading frame located down-stream of the coat protein gene, suggesting that it has a function in nematode transmission and that changes in this protein prevent vector transmission of the SP5 isolate of PEBV.
A major challenge to the development of a fundamental understanding of transport and retardation mechanisms of trace metal contaminants (<10 ppm) is their identification and characterization at the nanoscale. Atomic-scale techniques, such as conventional transmission electron microscopy, although powerful, are limited by the extremely small amounts of material that are examined. However, recent advances in electron microscopy provide a number of new analytical techniques that expand its application in environmental studies, particularly those concerning heavy metals on airborne particulates or water-borne colloids. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-energy-dispersive X-ray spectrometry (EDX), and energy-filtered TEM (EFTEM) can be effectively used to identify and characterize nanoparticles. The image contrast in HAADF-STEM is strongly correlated to the atomic mass: heavier elements contribute to brighter contrast. Gold nanocrystals in pyrite and uranium nanocrystals in atmospheric aerosols have been identified by HAADF-STEM and STEM-EDX mapping and subsequently characterized by high-resolution TEM (HRTEM). EFTEM was used to identify U and Fe nanocrystals embedded in an aluminosilicate. A rare, As-bearing nanophase, westerveldite (FeAs), was identified by STEM-EDX and HRTEM. The combined use of these techniques greatly expands the effective application of electron microscopy in environmental studies, especially when applied to metals of very low concentrations. This paper describes examples of how these electron microbeam techniques can be used in combination to characterize a low concentration of heavy metals (a few ppm) on nanoscale particles.
We report a case of dengue fever in a Boston-area health care worker with no recent history of travel but with mucocutaneous exposure to infected blood from a febrile traveler who had recently returned from Peru. Serologic tests confirmed acute dengue virus infection in both the traveler and the health care worker. We believe that this is the first documented case of dengue virus transmission via the mucocutaneous route. We present case reports and review other ways that dengue virus has been transmitted without a mosquito vector.
BACKGROUND: At the end of 2000 it was estimated that over 36 million people were living with the human immunodeficiency virus (HIV). This includes 1.4 million children less than 15 years of age. This is one of several reviews assessing the available evidence for preventing mother-to-child transmission of HIV infection. The other reviews will address other interventions, including Caesarean section, breast feeding, vaginal lavage and vitamin A supplementation. OBJECTIVES: To assess which antiretroviral therapies may be effective in decreasing the risk of mother-to-child transmission of HIV infection as well as their effect on neonatal and maternal mortality and morbidity. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register. We also searched conference abstracts from the International AIDS Conferences and Conference on Retroviruses and Opportunistic Infections. SELECTION CRITERIA: Randomised trials comparing any antiretroviral therapy aimed at decreasing the risk of mother-to-child transmission of HIV infection with placebo or no treatment, or any two or more antiretroviral therapies or regimens aimed at decreasing the risk of mother-to-child transmission of HIV infection. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed trial quality. MAIN RESULTS: Zidovudine monotherapy Any zidovudine regimen versus placebo significantly reduces the risk of mother-to-child transmission (Peto odds ratio (OR) 0.46, 95% confidence interval (CI) 0.35 to 0.60). Zidovudine also appears to decrease the risk of infant death within the first year of birth (OR 0.57, 95% CI 0.38 to 0.85) and the risk of maternal death (OR 0.32, 95% CI 0.16 to 0.66). There is no evidence that zidovudine influences the incidence of premature delivery (OR 0.86, 95% CI 0.57 to 1.29) or low birth weight (OR 0.74, 95% CI 0.53 to 1.04). The risk of transmission using a 'short-short' course of zidovudine (from 35 weeks in pregnancy for the mother and for the baby until 3 days old) was higher than the risk using a 'long-long' course (from 28 weeks in pregnancy for the mother and for the baby until 6 weeks old), (OR 2.55, 95% CI 1.26 to 5.18). However, the effectiveness of the 'long-short' course (from 28 weeks in pregnancy for the mother and for the baby until 3 days old) and the 'short-long' course (from 35 weeks in pregnancy for the mother and for the baby until 6 weeks old) did not differ from that of the 'long-long' course. Nevirapine One large randomised controlled trial demonstrates that nevirapine given to mothers as a single dose at the onset of labour and to babies as a single dose within 72 hours of birth is more effective than an intrapartum and post-partum regimen of zidovudine (OR 0.51, 95% CI 0.33 to 0.79). When nevirapine is given to mothers already receiving standard antiretroviral therapy, however, there appears to be no additional advantage (OR 1.10, 95% CI 0.42 to 2.86). Combination Therapy Preliminary findings of the effect of combination therapy using zidovudine and lamivudine (3TC) suggest a decrease in the risk of transmission when the combination is given during the antenatal and intrapartum period or during the intrapartum and postpartum period compared with placebo. There is no evidence that intrapartum zidovudine and lamivudine alone are sufficient to decrease the risk of transmission compared with placebo. REVIEWER'S CONCLUSIONS: Implications for practice The randomised trials included in this review provide evidence that short course zidovudine and single-dose nevirapine are effective therapies for reducing mother-to-child transmission of HIV. The challenge for low and middle income countries will be to institute this therapy in practice. In industrialised countries practice has already moved on from the current evidence and combination antiretroviral therapy aimed primarily at preventing disease progression in the mother is the standard of care. Implications for research The potential value of nevirapine used for longer durations in breastfeeding populations should be considered as it may further reduce the risk of mother-to-child transmission, particularly if combined with early weaning. On-going evaluation of combination antiretroviral therapy is essential and will have an immediate benefit for countries with the resources to adopt such treatment. The search for effective, affordable, safe and acceptable alternatives to antiretroviral therapy for reducing mother-to-child transmission in resource poor countries should remain on the research agenda.
BACKGROUND: At the end of 1998 over 33 million people were infected with the human immunodeficiency virus (HIV) and over one million children had been infected from their mothers. OBJECTIVES: The objective of this review was to assess what interventions may be effective in decreasing the risk of mother-to-child transmission of HIV infection as well as their effect on neonatal and maternal mortality and morbidity. SEARCH STRATEGY: The Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register were searched. SELECTION CRITERIA: Randomised trials comparing any intervention aimed at decreasing the risk of mother-to-child transmission of HIV infection compared with placebo or no treatment, or any two or more interventions aimed at decreasing the risk of mother-to-child transmission of HIV infection. DATA COLLECTION AND ANALYSIS: Trial quality assessments and data extraction were undertaken by the reviewer. MAIN RESULTS: Zidovudine Four trials comparing zidovudine with placebo involving 1585 participants were included. Compared with placebo, there was a significant reduction in the risk of mother-to-child transmission with any zidovudine (relative risk (RR) 0.54, 95% confidence interval (CI) 0.42-0.69). There is no evidence that 'long course therapy' is superior to 'short course therapy'. Nevirapine One trial compared intrapartum and postnatal nevirapine with intrapartum and postnatal zidovudine in 626 women, the majority of whom breast fed their infants. Compared with zidovudine, there was a significant reduction in the risk of mother-to-child transmission of HIV with nevirapine (RR 0.58, 95% CI 0.40-0.83). No trials are available comparing nevirapine with placebo. Caesarean section One trial comparing elective caesarean section with anticipation of vaginal delivery involving 436 participants was included. Compared with vaginal delivery, there was a significant reduction in the risk of mother-to-child transmission of HIV infection with caesarean section (RR 0.17, 95% CI 0.05-0.55). Immunoglobulin One trial comparing hyperimmune immunoglobulin plus zidovudine with non-specific immunoglobulin plus zidovudine involving 501 participants was included. The addition of hyperimmune immunoglobulin to zidovudine does not appear to have any additional effect on the risk of mother-to-child transmission (RR 0.67, 95% CI 0.29-1.55). REVIEWER'S CONCLUSIONS: Zidovudine, nevirapine and delivery by elective caesarean section appear to be very effective in decreasing the risk of mother-to-child transmission of HIV infection.
OBJECTIVES: To determine the proportion of HIV-1-infected infants infected in utero and intrapartum, the relationship between transmission risk factors and time of transmission, and the population-attributable fractions for maternal viral load. DESIGN: Prospective cohort study of 218 formula-fed infants of HIV-1-infected untreated mothers with known infection outcome and a birth HIV-1-positive DNA PCR test result. METHODS: Transmission in utero was presumed to have occurred if the birth sample (within 72 h of birth) was HIV-1-positive by PCR; intrapartum transmission was presumed if the birth sample tested negative and a later sample was HIV-1-positive. Two comparisons were carried out for selected risk factors for mother-to-child transmission: infants infected in utero versus all infants with a HIV-1-negative birth PCR test result, and infants infected intrapartum versus uninfected infants. RESULTS: Of 49 infected infants with an HIV-1 birth PCR result, 12 (24.5%) [95% confidence interval (CI), 14 -38] were presumed to have been infected in utero and 37 (75.5%) were presumed to have been infected intrapartum. The estimated absolute overall transmission rate was 22.5%; this comprised 5.5% (95% CI, 3-9) in utero transmission and 18% (95% CI, 13-24) intrapartum transmission. Intrapartum transmission accounted for 75.5% of infections. High maternal HIV-1 viral load (> median) was a strong risk factor for both in utero [adjusted odds ratio (AOR) 5.8 (95% CI, 1.4-38.8] and intrapartum transmission (AOR, 4.4; 95% CI, 1.9-11.2). Low birth-weight was associated with in utero transmission, whereas low maternal natural killer cell and CD4(+) T-lymphocyte percentages were associated with intrapartum transmission. The population-attributable fraction for intrapartum transmission associated with viral load > 10 000 copies/ml was 69%. CONCLUSIONS: Our results provide further evidence that most perinatal HIV-1 transmission occurs during labor and delivery, and that risk factors may differ according to time of transmission. Interventions to reduce maternal viral load should be effective in reducing both in utero and intrapartum transmission.
BACKGROUND: Hepatitis C virus (HCV) vertical transmission studies have reported conflicting findings, possibly due to differences in HCV transmission risk factors among maternal populations, or to methodological differences. METHODS: Systematic review of worldwide published and unpublished HCV vertical transmission studies. Standardized diagnostic criteria were applied to minimize methodological differences, and transmission rates recalculated according to maternal HCV viraemic and human immunodeficiency virus (HIV) infection status. RESULTS: In all, 976 eligible infants from 28 studies were followed up sufficiently for recalculation of transmission rates. Overall transmission rates were less than 10% in 8/12 studies of HIV negative mothers, compared with 2/7 studies comprising at least 50% HIV-coinfected mothers. Rates from 409 viraemic mothers in 15 studies ranged from 0% to 41%, being less than 10% from HIV negative mothers in 6/13 studies and from HIV positive mothers in 1/6 studies. Nine studies measured maternal viraemia levels, with only 2/30 transmitting mothers having < 10(6) copies/ml of HCV RNA. Eight transmissions were identified overall from non-viraemic mothers. Significant transmission rate variation remained after accounting for maternal viraemia and HIV coinfection, possibly due to differences in other vertical transmission risk factors, in frequencies of postnatal transmission, or residual differences in study methodologies. CONCLUSIONS: Overall, HCV transmission is largely restricted to infants born to HCV viraemic mothers, and low risks among most HIV negative mothers may be due to lower HCV viraemia levels. International agreement on standardized diagnostic criteria for HCV vertical transmission would facilitate pooling of individual findings, to allow more precise transmission estimates and further investigation of risk factors.
BACKGROUND: Little information is available about the timing of mother-to-child transmission of hepatitis C virus (HCV), and no interventions to decrease transmission rates have been identified. We examined the effect of risk factors, including mode of delivery, on the vertical transmission rate. METHODS: Data from HCV-infected women and their infants from three hospitals in Ireland and from a British Paediatric Surveillance Unit study of infants born to HCV-infected mothers were used to estimate the vertical transmission rate and risk factors for transmission. We used a probabilistic model using methods that simultaneously estimated the time to HCV-antibody loss in uninfected infants and the diagnostic accuracy of PCR tests for HCV RNA. FINDINGS: 441 mother-child pairs from the UK (227) and Ireland (214) were included. 50% of uninfected children became HCV-antibody negative by 8 months and 95% by 13 months. The estimated specificity of PCR for HCV RNA was 97% (95% CI 96-99) and was unrelated to age; sensitivity was only 22% (7-46) in the first month but rose sharply to 97% (85-100) thereafter. The vertical transmission rate was 6.7% (4.1-10.2) overall, and 3.8 times higher in HIV coinfected (n=22) than in HIV-negative women after adjustment for other factors (p=0.06). No effect of breastfeeding on transmission was observed, although only 59 women breastfed. However, delivery by elective caesarean section before membrane rupture was associated with a lower transmission risk than vaginal or emergency caesarean-section delivery (odds ratio 0 [0-0.87], p=0.04, after adjustment for other factors). INTERPRETATION: The low sensitivity of HCV RNA soon after birth and the finding of a lower transmission rate after delivery by elective caesarean section suggest that HCV transmission occurs predominantly around the time of delivery. If the findings on elective caesarean section are confirmed in other studies, the case for antenatal HCV testing should be reconsidered.
OBJECTIVES: Heterosexual transmission has long been considered the predominant route of transmission of HIV-1 in sub-Saharan Africa. However, some have argued that unsafe medical injections account for the majority of transmission in this region. GOAL: The goal of this study was to compare the HIV-1 epidemics associated with different transmission routes. STUDY: An age-structured deterministic compartmental model of HIV-1 transmission through both sexual contact and unsafe injections was developed and simulations of sexual transmission and iatrogenic transmission were compared with observed prevalence. RESULTS: Iatrogenic transmission probabilities and numbers of unsafe injections required to generate observed prevalence are unfeasibly high. Simulations of sexually transmitted HIV-1 generate observed prevalence using transmission probabilities and average partner change rates that are within plausible bounds. CONCLUSIONS: Heterosexual transmission seems a more likely route of transmission in the region. However, heterogeneity in contact patterns is of key importance. Further information on groups who are likely to receive more injections is required.
Elevated levels of estradiol enhance learning in mammals, including humans, likely a result of hormone-induced heightened plasticity at CA3-CA1 synapses. The increase in long-term potentiation (LTP) magnitude is considered to be a consequence of the estradiol-induced increase in dendritic spine density and NMDA receptor (NMDAR)-mediated transmission; however, direct evidence linking these changes together is lacking. Alternatively, alterations in GABAergic inhibition or presynaptic release probability could contribute. Here, we show in time course studies using hippocampal slices from estradiol-treated ovariectomized rats that the LTP magnitude is increased only when spine density is increased simultaneously with an increase in NMDAR transmission relative to AMPA receptor (AMPAR) transmission, with no role for alterations in GABAergic inhibition or release probability. With time after hormone treatment, AMPAR transmission gradually increases during the maintained increase in spine density and NMDAR transmission. Eventually, the balance between NMDAR and AMPAR transmission is reestablished, and the LTP magnitude is no longer increased. Blocking genomic estrogen receptors prevents the heightened spine density, NMDAR transmission, and LTP magnitude, suggesting a tight mechanistic coupling between these morphological and functional changes. Thus, we propose that the hormone-induced increase in functional synapse density alone is not sufficient to support heightened plasticity. Rather, estradiol increases LTP via enhancing NMDAR transmission, likely through receptor insertion into newly formed or preexisting synapses. Later, when excitability in the circuit is at its highest and spine density remains elevated, the LTP magnitude is no longer increased, probably as a consequence of the delayed increase in AMPAR transmission that resets the balance between NMDAR and AMPAR transmission.
OBJECTIVES: To evaluate the impact of perinatal zidovudine use on the risk of perinatal transmission of HIV and to determine risk factors for transmission among women using perinatal zidovudine. DESIGN: Prospective cohort study of 1533 children born to HIV-infected women between 1985 and 1995 in four US cities. METHODS: The association of potential risk factors with perinatal HIV transmission was assessed with univariate and multivariate statistics. RESULTS: The overall transmission risk was 18% [95% confidence interval (CI), 16-21]. Factors associated with transmission included membrane rupture > 4 h before delivery [relative risk (RR), 2.1; 95% CI, 1.6-2.7], gestational age < 37 weeks (RR, 1.8; 95% CI, 1.4-2.2), maternal CD4+ lymphocyte count < 500 x 10(6) cells/l (RR, 1.7; 95% CI, 1.3-2.2), birthweight < 2500 g (RR, 1.7; 95% CI, 1.3-2.1), and antenatal and neonatal zidovudine use (RR, 0.6; 95% CI, 0.4-0.9). For infants exposed to zidovudine antenatally and neonatally, the transmission risk was 13% overall but was significantly lower following shorter duration of membrane rupture (7%) and term delivery (9%). The transmission risk declined from 22% before 1992 to 11% in 1995 (P < 0.001) in association with increasing zidovudine use and changes in other risk factors. CONCLUSIONS: Perinatal HIV transmission risk has declined with increasing perinatal zidovudine use and changes in other factors. Further reduction in transmission for women taking zidovudine may be possible by reducing the incidence of other potentially modifiable risk factors, such as long duration of membrane rupture and prematurity.
Natural Plasmodium vivax malaria infections in man evoke anti-gamete transmission blocking antibodies which influence the infectivity of malaria patients to the vector mosquito. In this study, entomological, immunological and parasitological data obtained through the monitoring of an epidemic of human vivax malaria in Sri Lanka were used in a mathematical simulation to assess the effect of naturally induced transmission blocking immunity on malaria transmission. A mathematical model to describe malaria transmission accounting for transmission blocking immunity was developed from the basic differential equations originally stated by R. Ross and the epidemic was simulated using the available data. An attempt was made to predict the monthly malaria incidence by means of the mathematical simulation, with and without accounting for transmission blocking immunity. A plausible mathematical solution of the epidemic could be obtained when transmission blocking immunity was accounted for, and it was not possible to obtain such a plausible solution in the absence of immunity. Thus, the postulated occurrence of transmission blocking immunity was essential to describe adequately this malaria epidemic, indicating that, at least in epidemic situations, naturally occurring transmission blocking immunity has a controlling influence on malaria incidence.
A simple, visual representation of spatial aspects of malaria transmission in successive snap-shots in time, is presented. The spatial components of the simulation involve (i) the identification of mosquito vector breeding sites of defined shape and area, (ii) the identification of a zone of malaria transmission determined by the shapes and areas of the vector breeding sites and the distance from these sites that the mosquitoes disperse, (iii) a human population dispersed in relation to the malaria transmission zone, (iv) perimeters around each individual human within which his or her infection can be transmitted by the local vector mosquitoes. The intensity of transmission within a malaria transmission zone is given by a number which is the number of new cases of malaria that each existing case will distribute through the human population within the duration of an infection. The simulation has been used here to examine the effects of vaccination against malaria transmission. Different levels of vaccine coverage are represented under endemic and epidemic malaria. The consequences of full or partial coverage of a zone of malaria transmission are also examined. The results are numerically compatible with the predictions of previous simple mathematical simulations of malaria transmission and interventions. The present simulation allows the nature of malaria transmission and the effects of interventions to be communicated easily and directly to an audience. It could have practical value in discussions of malaria control strategies with health planners.
OBJECTIVES: To develop an animal model to study transmucosal lentivirus transmission, and to determine whether topical application of contraceptive jelly can block transmission by an infected cell incoulum. DESIGN: Feline immunodeficiency virus (FIV), a lentivirus similar to HIV, causes an AIDS-like disease in domestic cats. HIV is transmitted primarily across mucosal surfaces, and infected cells may be important in this transmission. We tested the ability of FIV-infected cells to transmit infection across the vaginal, rectal and oral mucosa of the cat, and whether a vaginal contraceptive jelly could prevent such transmission. METHODS: An inoculum consisting of 2 million FIV-infected primary cat T cells was administered vaginally, rectally or orally to female cats that had received either no pretreatment or pretreatment with a contraceptive jelly containing the detergent nonoxynol-9 as spermicide. Transmission was detected by monitoring recipient animals for viral antibodies and by viral cultures of blood leukocytes. RESULTS: A single dose of the infected cell inoculum efficiently transmitted FIV infection when delivered into the vagina or rectum (10 out of 11 animals became infected). Pretreatment of the vagina (five animals) or rectum (four animals) with contraceptive jelly protected all animals from transmission by the highly infectious inoculum. CONCLUSIONS: The cat/FIV model provides an efficient means to study transmucosal transmission of lentivirus infections, and for assessing vaginal barrier methods that could block transmission. One such method, nonoxynol-9 contraceptive jelly, effectively prevents transmucosal transmission by an FIV-infected cell inoculum.
BACKGROUND: An understanding of the risk and timing of mother-to-child transmission of HIV-1 in the postnatal period is important for the development of public-health strategies. We aimed to estimate the rate and timing of late postnatal transmission of HIV-1. METHODS: We did an international multicentre pooled analysis of individual data from prospective cohort studies of children followed-up from birth born to HIV-1-infected mothers. We enrolled all uninfected children confirmed by HIV-1-DNA PCR, HIV-1 serology, or both. Late postnatal transmission was taken to have occurred if a child later became infected. We calculated duration of follow-up for non-infected children from the time of negative diagnosis to the date of the last laboratory follow-up, or for infected children to the mid-point between the date of last negative and first positive results. We stratified the analysis for breastfeeding. FINDINGS: Less than 5% of the 2807 children in four studies from industrialised countries (USA, Switzerland, France, and Europe) were breastfed and no HIV-1 infection was diagnosed. By contrast, late postnatal transmission occurred in 49 (5%) of 902 children in four cohorts from developing countries, in which breastfeeding was the norm (Rwanda [Butare and Kigali], Ivory Coast, Kenya), with an overall estimated risk of 3.2 per 100 child-years of breastfeeding follow-up (95% CI 3.1-3.8), with similar estimates in individual studies (p=0.10). Exact information on timing of infection and duration of breastfeeding was available for 20 of the 49 children with late postnatal transmission. We took transmission to have occurred midway between last negative and first positive HIV-1 tests. If breastfeeding had stopped at age 4 months transmission would have occurred in no infants, and in three if it had stopped at 6 months. INTERPRETATION: Risk of late postnatal transmission is consistently shown to be substantial for breastfed children born to HIV-1-positive mothers. This risk should be balanced against the effect of early weaning on infant mortality and morbidity and maternal fertility.
To determine the rate and risk factors for human immunodeficiency virus (HIV)-1 subtype E perinatal transmission, with focus on virus load, pregnant HIV-infected women and their formula-fed infants were followed prospectively in Bangkok. Of 281 infants with known outcome, 68 were infected (transmission rate, 24.2%; 95% confidence interval, 19.3%-29.6%). Transmitting mothers had a 4.3-fold higher median plasma HIV RNA level at delivery than did nontransmitters (P<.001). No transmission occurred at <2000 copies/mL. On multivariate analysis, prematurity (adjusted odds ratio [AOR], 4.5), vaginal delivery (AOR, 2.9), low NK cell percentage (AOR, 2.4), and maternal virus load were associated with transmission. As RNA quintiles increased, the AOR for transmission increased linearly from 4.5 to 24.8. Two-thirds of transmission was attributed to virus load>10,000 copies/mL. Although risk is multifactorial, high maternal virus load at delivery strongly predicts transmission. This may have important implications for interventions designed to reduce perinatal transmission.