Characteristics of HIV Infected Adolescents in Latin America: Results from the NISDI Pediatric Study

Abstract

Objective: HIV-infected adolescents are a heterogeneous population; source of infection, immunodeficiency severity and antiretroviral (ARV) experience vary. Here, we describe youth followed in an observational study at Latin American sites of the NICHD International Site Development Initiative (NISDI).

Methods: The NISDI pediatric protocol is an ongoing prospective cohort study that collects demographic, clinical, immunologic, virologic and medication data. Youth were enrolled at 15 sites in Brazil, Argentina and Mexico between 2002 and 2006. HIV-infected subjects aged 12–21 years at the time of enrollment were analyzed.

Results: Data from 120 HIV-infected youth were analyzed. Sixty-nine (58%) had acquired HIV through vertical transmission (VT); 51(42%) via horizontal transmission (HT). Twenty-eight percent of the VT group were not diagnosed until they were ≥10 years of age. Ninety-one percent of the VT group and 46% of the HT were receiving ARV at enrollment. Modes of HT included sexual (ST), blood product transfusion (BPT) and unknown (U). Severe immunodeficiency was frequent (21%) in the ST group. Low BMI was frequent in the VT and BPT sub-groups. Utilization of HAART increased over the course of the study, but viral suppression was present in only 38% of the VT group and 37% of the HT group at study end.

Conclusions: This cohort of HIV-infected adolescents in Latin America displayed a diverse epidemiologic pattern. Care providers must be prepared to address the diverse needs and challenges of this population. The levels of virologic suppression achieved were inadequate. Further research into appropriate interventions for this population is urgently needed.

Introduction

HIV specialists are being challenged globally by the care of HIV-infected adolescents that compose a diverse population in terms of severity of disease and antiretroviral experience [1–3]. Sources of infection among individuals of this age group include mother-to-child transmission (MTCT) (vertical), sexual activity, exposure to contaminated blood products and intravenous drug use. In Brazil, as of June 2009, there were 11 786 reported cases of AIDS in patients aged 13–19 years (2.2% of 544 823 cases reported in the country) [4].

Many HIV pediatric services have been following vertically and blood transfusion infected individuals since childhood. An increasing number of children infected by MTCT and by blood product transfusion are surviving into adolescence and young adulthood in countries where antiretroviral (ARV) drugs are available [5–8]. From a clinical standpoint, patients diagnosed early in life may have experienced multiple ARV regimens, including what would now be considered suboptimal therapy, making treatment options scarce as they transition into adolescence.

Despite rapid disease progression in many HIV-infected infants, some vertically infected children can have slow progression of disease and not be diagnosed until late in childhood or early adolescence [9–11]. Family serological screening for HIV has been increasing as a consequence of the broad implementation of strategies to prevent MTCT and promotes the diagnosis of these older children and adolescents who were otherwise not suspected of having HIV due to mild or no symptoms.

Adolescents infected through sexual activity are a major proportion of newly infected individuals worldwide; according to the World Health Organization over half of new HIV-1 infections occur in youths aged 15–24 years [12]. Reports from the Pan American Health Organization show that in Latin America up to 50% of youths under the age of 17 years are sexually active, 15% of those who are sexually active acquire a sexually transmitted disease each year and 25% of all infants are born to adolescents [13].

The main objective of this study was to describe the clinical and laboratory characteristics of HIV-infected adolescents at diagnosis, enrollment and at the end of up to 4 years of follow-up in Latin American sites in the NICHD International Site Development Initiative (NISDI) cohort.

Materials and Methods

Study population and design

The NICHD International Site Development Initiative (NISDI) pediatric protocol is a prospective cohort study of HIV-infected and HIV-exposed youth up to the age of 21 years enrolled at 15 sites in Brazil, Argentina and Mexico. Baseline assessments included demographic, clinical, immunologic and virologic information, medical history, diagnoses and ARV. Follow-up visits occurred every 6 months. The protocol was reviewed and approved by the Institutional Review Boards at each site, national review boards as necessary, NICHD and the data management and statistical center (Westat). Informed consent was obtained from parents/legal guardians or from participants, depending on age. Assent was obtained from minor subjects when developmentally appropriate. Additional details describing this protocol and cohort have been published [14].

This investigation focuses on HIV-infected patients who were 12–21 years of age at the time of enrollment between 2002 and 2006. These adolescents were categorized into two major groups: vertical (i.e. perinatal) transmission or horizontal transmission. Youth in the vertical group were further subdivided based on age at diagnosis (≤9 years vs. ≥10 years). Youth in the horizontal group were further sub-divided based upon mode of transmission: sexual transmission (sexual), infected via blood product transfusion (transfusion) and unknown mechanism of infection (unknown).

Statistical analysis

Descriptive statistics including mean, median and range were used to describe continuous variables and percents were used to describe categorical variables. Statistical comparisons were made between the vertical and horizontal groups using the t-test for continuous variables and the Fisher’s exact test for categorical variables. However, due to the heterogeneity of the horizontal transmission group and the small number of subjects in the transfusion and unknown subgroups, statistical comparison tests were computed for the vertical vs. sexual groups only. Statistical analyses were performed using SAS 9.1 software (SAS Institute Inc., Cary, NC, USA).

Results

As of 1 October 2006, there were 794 HIV-infected children enrolled in the NISDI pediatric protocol. Six hundred and seventy four (85%) were <12 years of age at enrollment and were thus not included in this analysis. The study population for this analysis was the remaining 120 HIV-infected subjects who were aged 12–21 years at the time of enrollment. The median (range) duration of follow-up for the vertical and horizontal group was 34 (17–43) months and 35 (<1–47) months, respectively. There were two deaths during follow-up. One subject in the vertical group died of suspected pneumonia associated with dehydration, hypoglycemia and anemia. The other subject was in the horizontal group and died of septicemia.

The demographic and clinical characteristics of the subjects are shown in Table 1. There were 69 adolescents in the vertical group and 51 in the horizontal group. Among the 69 vertically infected adolescents, 19 (28%) were diagnosed at the age of ≥10 years. Among the 51 horizontally infected adolescents, 33 (65%) were sexually infected, 10 (20%) were infected by transfusion and eight (16%) by unknown reasons. The vertical group was younger at enrollment and younger at the time of first available positive HIV test than the horizontal group.

Table 1.

Demographic and clinical characteristics of youth with vertically and horizontally acquired infection

	Vertically acquired	Horizontally acquired sexual		Horizontally acquired other
	(N = 69)	(N = 33)	p-value*	Transfusion (N = 10)	Unknown (N = 8)
Country, N (%)			<0.001
Argentina	9 (13.0)	10 (30.3)		1 (10.0)	2 (25.0)
Brazil	49 (71.0)	7 (21.2)		8 (80.0)	5 (62.5)
Mexico	11 (15.9)	16 (48.5)		1 (10.0)	1 (12.5)
Gender, N (%)			0.5133
Male	26 (37.7)	10 (30.3)		5 (50.0)	4 (50.0)
Female	43 (62.3)	23 (69.7)		5 (50.0)	4 (50.0)
Age at enrollment, N (%)			<0.001
12–14	59 (85.5)	1 (3.0)		4 (40.0)	3 (37.5)
15–19	10 (14.5)	22 (66.7)		6 (60.0)	4 (50.0)
20–21	0 (0.0)	10 (30.3)		0 (0.0)	1 (12.5)
Primary caregiver, N (%)			<0.001
One or more biological parents	28 (40.6)	15 (45.5)		9 (90.0)	4 (50.0)
Other relative	22 (31.9)	1 (3.0)		0 (0.0)	1 (12.5)
Adoptive parents	3 (4.3)	0 (0.0)		0 (0.0)	0 (0.0)
Foster care manager	16 (23.2)	0 (0.0)		1 (10.0)	1 (12.5)
Partner/Husband	0 (0.0)	4 (12.1)		0 (0.0)	0 (0.0)
Self	0 (0.0)	13 (39.4)		0 (0.0)	2 (25.0)
Age (years) at first available positive HIV test, median (range)
	7 (0–17)	18 (9–20)	<0.001	10 (4–14)	12.5 (2–21)
CD4 count (cells mm−3) at enrollment, N (%)			0.082
≥500	35 (50.7)	11 (34.4)		2 (22.2)	3 (37.5)
200–499	29 (42.0)	14 (43.8)		6 (66.7)	2 (25.0)
<200	5 (7.2)	7 (21.9)		1 (11.1)	3 (37.5)
Missinga	0	1		1	0
CD4 count (cells mm−3) at end of follow-up, N (%)			0.041
≥500	36 (52.9)	12 (36.4)		2 (20.0)	4 (50.0)
200–499	24 (35.3)	20 (60.6)		6 (60.0)	1 (12.5)
<200	8 (11.8)	1 (3.0)		2 (20.0)	3 (37.5)
Missinga	1	0		0	0
Viral load (HIV RNA copies ml−1) at enrollment, N (%)			0.927
<400	22 (31.9)	11 (36.7)		4 (40.0)	2 (25.0)
400 to <10 000	21 (30.4)	9 (30.0)		3 (30.0)	2 (25.0)
≥10 000	26 (37.7)	10 (33.3)		3 (30.0)	4 (50.0)
Missinga	0	3		0
Viral load (HIV RNA copies ml−1) at end of follow-up, N (%)			0.834
<400	26 (37.7)	14 (42.4)		3 (30.0)	2 (25.0)
400 to <10 000	20 (29.0)	8 (24.2)		4 (40.0)	4 (50.0)
≥10 000	23 (33.3)	11 (33.3)		3 (30.0)	2 (25.0)
Clinical CDC classificationb at enrollment, N (%)			<0.001
N	9 (13.0)	25 (75.8)		1 (10.0)	2 (25.0)
A	17 (24.6)	2 (6.1)		1 (10.0)	1 (12.5)
B	27 (39.1)	3 (9.1)		5 (50.0)	2 (25.0)
C	16 (23.2)	3 (9.1)		3 (30.0)	3 (37.5)
Clinical CDC classificationb at end of follow-up, N (%)			<0.001
N	8 (11.6)	25 (75.8)		1 (10.0)	2 (25.0)
A	16 (23.2)	2 (6.1)		1 (10.0)	1 (12.5)
B	26 (37.7)	3 (9.1)		5 (50.0)	2 (25.0)
C	19 (27.5)	3 (9.1)		3 (30.0)	3 (37.5)
BMI-for-agecN (%)			0.480
Underweight	10 (14.7)	3 (9.1)		2 (20.0)	1 (12.5)
Normal	52 (76.5)	25 (75.8)		8 (80.0)	7 (87.5)
Risk for overweight	3 (4.4)	4 (12.1)		0 (0.0)	0 (0.0)
Overweight	3 (4.4)	1 (3.0)		0 (0.0)	0 (0.0)
Missinga/Not availablec	1	0		0	0
Number of ARV drugs before enrollment, N (%)			<0.001
0	3 (4.3)	8 (24.2)		1 (10.0)	2 (25.0)
1	0 (0.0)	4 (12.1)		0 (0.0)	0 (0.0)
2–4	28 (40.6)	17 (51.5)		2 (20.0)	3 (37.5)
≥5	38 (55.1)	4 (12.1)		7 (70.0)	3 (37.5)
ARV regimens through end of follow-up, N (%)			<0.001
0	3 (4.3)	6 (18.2)		1 (10.0)	1 (12.5)
1	9 (13.0)	12 (36.4)		0 (0.0)	3 (37.5)
2	11 (15.9)	8 (24.2)		0 (0.0)	1 (12.5)
≥3	46 (66.7)	7 (21.2)		9 (90.0)	3 (37.5)
Types of regimensd at enrollment, N (%)			<0.001
HAART+PI	27 (39.1)	3 (9.1)		5 (50.0)	2 (25.0)
HAART+NNRTI	11 (15.9)	3 (9.1)		3 (30.0)	1 (12.5)
HAART+PI+NNRTI	5 (7.2)	2 (6.1)		0 (0.0)	0 (0.0)
Not HAART	20 (29.0)	0 (0.0)		1 (10.0)	3 (37.5)
No ARV	6 (8.7)	25 (75.8)		1 (10.0)	2 (25.0)
Types of regimensd at last study visit, N (%)			<0.001
HAART+PI	31 (44.9)	8 (24.2)		3 (30.0)	3 (37.5)
HAART+NNRTI	19 (27.5)	9 (27.3)		5 (50.0)	1 (12.5)
HAART+PI+NNRTI	5 (7.2)	2 (6.1)		0 (0.0)	0 (0.0)
Not HAART	13 (18.8)	2 (6.1)		1 (10.0)	3 (37.5)
No ARV	1 (1.4)	12 (36.4)		1 (10.0)	1 (12.5)

*Comparison of vertically acquired vs. horizontally acquired sexual.

^aMissing (or not available) values not included in percentage or p-value calculations.

^bFrom the 1994 revised CDC classification for children [CDC 1994]. Category B is non-AIDS-defining events. The category of AIDS-defining events (C) is a composite of the adult and pediatric CDC classification systems [16, 17].

^cUnderweight = BMI-for-age <5th percentile; normal = 5–84th; risk for overweight = 85–94th; overweight = ≥95th. National Center for Health Statistics of the Centers for Disease Control and Prevention (CDC) [28]. BMI-for-age tables available only for ages ≤19 or younger. Age 19 values used for subjects 20 or 21 years old.

^dHAART+PI = highly active antiretroviral therapy (HAART) regimens containing at least two nucleoside reverse transcriptase inhibitors (NRTI) and at least one protease inhibitor (PI); HAART+NNRTI = HAART regimens containing at least two NRTI and a non-nucleoside reverse transcriptase inhibitor (NNRTI); HAART+PI+NNRTI = HAART regimens containing at least two NRTI plus one or more PI and NNRTI; Not-HAART = regimens containing one or more NRTI only; and No ARV = subjects not receiving ARV.

From the time of enrollment to the end of follow-up, the percentage of subjects with CD4 < 200 increased slightly (from 7.2% to 11.8%) in the vertical group but decreased (from 21.9% to 3.0%) in the sexual group. This decrease was not observed in the other horizontally acquired subgroups. The viral load was not significantly different between the vertical and sexual groups at enrollment or at the end of follow-up. At the end of follow-up, ∼40% of each group was suppressed (<400 copies ml⁻¹) and 33% had viral loads above 10 000 copies ml⁻¹. CDC classification did not change during the follow-up period, but was significantly different between the vertical and horizontal groups (e.g. 27.5% of the vertical group was class C vs. 9.1% in the horizontal group). Body mass index (BMI) for age was not significantly different between the vertical and sexual groups, although there were slightly more vertical subjects in the underweight category and more sexual subjects in the risk for overweight category. Approximately 75% of each group was in the normal range.

ARV use was analyzed according to the number of individual drugs, number of treatment regimens (i.e. ARV combinations) and type of treatment regimen. There were statistically significant differences between the vertical and sexual groups for each of these ARV measures. Among the vertical group, 66 (96%) had used two or more ARV drugs and 38 (55%) had been exposed to at least five ARV drugs by the time they enrolled into protocol. Among those diagnosed at the age of ≥10 years, only 37% had been exposed to five or more drugs prior to enrollment. By the end of follow-up, 99% of subjects were receiving ARV therapy with 54 (80%) receiving HAART. Among the sexual group, 76% were not receiving ARV at enrollment and only 24% were on HAART. By the end of the study period, only 36% were not receiving ARV and 58% were on HAART.

Table 2 gives a listing of non-AIDS and AIDS-defining events for the vertical and horizontal groups reported either before or after enrollment. Among vertical adolescents the majority of events occurred before enrollment. Following enrollment, 10 subjects experienced 12 new events including five AIDS defining diagnoses. The AIDS defining events were: esophageal or pulmonary candidiasis; disseminated or extrapulmonary tuberculosis; Pneumocystis jeroveci pneumonia; progressive multifocal leukoencephalopathy; and toxoplasmosis of the brain. Among the horizontal adolescents, the majority of non-AIDS and AIDS-defining events also occurred before enrollment. Only two subjects were diagnosed with four non-AIDS-defining events during the study period. No AIDS-defining events were diagnosed during the study period among the horizontal group.

Table 2.

Diagnoses reported either before or after enrollment

	Vertically acquired	Horizontally acquired	Total
Total number of eventsa	67	32	99
AIDS defining events
Candidiasis, esophageal or pulmonary	1		1
Cytomegalovirus disease with onset of symptoms at age >1 month	2	1	3
Encephalopathy	3		3
Kaposi’s sarcoma		1	1
Lymphoma, small, non-cleaved cell	1		1
Tuberculosis, disseminated or extrapulmonary	2	2	4
Pneumocystis jeroveci pneumonia	1		1
Progressive multifocal leukoencephalopathy	2		2
Toxoplasmosis of the brain with onset at >1 month of age		1	1
Wasting syndrome	1	6	7
Non-AIDS defining events
Serious Bacterial infections (single episodes of meningitis, pneumonia, septicemia or abscess of a internal organ or body cavity)	25	9	34
Diarrhea, recurrent or chronic	5	2	7
Herpes zoster (shingles) involving at least two distinct episodes or >1 dermatome	3	4	7
Recurrent or persistent upper respiratory infection, sinusitis or otitis media	5	1	6
Parotitis	3	2	5
Lymphoid interstitial pneumonia (lip) or pulmonary lymphoid hyperplasia complex	3	1	4
Cardiomyopathy	2	1	3
Thrombocytopenia (≤100 000 mm−3) persisting ≥30 days	3		3
Anemia (<8 gm dl−1) persisting ≥30 days	2		2
Dermatitis	1	1	2
Herpes simplex virus (HSV) stomatitis recurrent (>2 episodes w/in 1 year)	1		1
Neutropenia (<1000 mm−3) persisting ≥30 days	1		1

^aModified from CDC definitions [16, 17].

Discussion

This report describes a cohort of 120 HIV-infected adolescents enrolled in the NISDI pediatric protocol as of late 2006. Given the paucity of data about HIV-infected adolescent populations in Latin America, the value of our study lies in the diversity of the cohort (which allowed subgroup analysis of both vertically and horizontally infected adolescents), and the intensity and length of its follow-up.

The median age at the first positive HIV test for subjects in the vertical group was 7 years, which is higher than some European cohorts [9, 15] but similar to the series reported by Grubman in 1995 in the USA [1]. Screening of entire families for HIV should be part of the standard of care when an HIV-infected individual is identified whenever possible. In addition, a higher index of suspicion regarding the possibility of HIV infection in children on the part of providers is required and could lead to greater opportunities for identification and early treatment of this population. The greater availability of ARV treatment for children should encourage this practice. Our study, however, shows that in Latin America delay of diagnosis in children is not rare. Five of the 19 vertical subjects (26%) diagnosed at age ≥10 years were classified as CDC category N at enrollment and remained asymptomatic with respect to HIV infection throughout the study [16, 17]. Another eight subjects (42%) in the same group were classified as CDC category B at enrollment based on a history of a single episode of pneumonia and/or other bacterial infection. This sub-group of apparent slow progressors emphasizes the importance of considering the possibility of HIV infection during the routine care of pediatric patients, especially those presenting with CDC category B diagnoses since the incubation period of vertically acquired HIV infection can be quite variable [18]. The European Collaborative Study [10] had similar findings with 18% of vertically infected children diagnosed at a median age of 11.4 years. Providers must remain aware of the possibility of undiagnosed vertically acquired HIV even in asymptomatic or minimally symptomatic older children and must consider HIV as they review any patient’s history, physical exam and family history. Approximately 12% of our adolescents had evidence of poor nutrition (BMI <5th percentile) with slightly higher percentages (15–20%) observed among the vertical and non-sexual horizontal subgroups. Nutritional status is a major determinant of quality of life, and low BMI has been associated with HIV disease progression [19, 20].

The vertical and transfusion sub-groups experienced a slight increase in the proportion of patients with severe immunodeficiency during study follow-up. Other authors have observed that adolescents infected by these two modes of transmission have comparable progression of HIV-1 disease [2, 3], although faster progression among vertically infected children was observed prior to the availability of HAART [21].

Among the sexually infected group the percentage of subjects with CD4 counts <200 cells mm⁻³ decreased from 22% at enrollment to 3% at the end of study follow-up. The percentage of this group not using ARV also decreased from 76% to 36% during this time period. The high occurrence of advanced immunodeficiency among sexually infected adolescents supports the findings of the REACH Project where 30% of subjects aged 12–18 years old had AIDS at study entry [22] and reinforces the need of further study of disease progression when HIV-1 is acquired through sexual activity at an early age.

Only 42% of subjects in the sexual group and 37% in the horizontal group overall had HIV RNA levels <400 copies ml⁻¹ at the last study visit. Likewise, in the vertical group 38% of subjects achieved this level of viral suppression. Thus, the proportion of subjects achieving viral suppression in every group was far from optimal notwithstanding the fact that a greater number of subjects were being prescribed HAART by the end of the study. A recent study in Brazil found 53% of adolescents with undetectable viral load [23]. Difficulties in achieving and maintaining virologic suppression in adolescents have been reported in other studies as well [24–26]. Pediatric AIDS Clinical Trials Group (PACTG) study 381 was an observational study that followed a US cohort of 120 adolescents initiating HAART. Only 24% of adolescents had an undetectable viral load after three years of follow-up [26, 27]. The main predictors of unsuccessful virologic suppression among adolescents in this cohort were poor adherence and higher baseline viral loads. Difficulties with adherence among this age group have also been well-documented in other studies, appear to be multifactorial and can include issues surrounding concurrent depression, complications in daily routines and medication-related physical and psychological adverse effects [25].

Some of the limitations of our study are a consequence of its observational design. For example, most of the subjects infected via vertical and sexual modes were female while those infected via transfusion or unknown modes were evenly distributed with respect to gender. Female subjects may have already been participating more actively in the health care system than their male counterparts, as many were recruited through referrals from sexually transmitted disease and pregnancy clinics. Also, although we had representation from three Latin American countries, 58% of our subjects were enrolled from 11 sites located in large urban areas in the southern and southeastern regions of Brazil, where the majority of cases have been reported [4]. This overrepresentation of Brazilian sites and subjects may limit the generalizability of the study across a wider variety of Latin American settings.

Despite these limitations, our study demonstrates the heterogeneous nature of the HIV-infected adolescent population, which consists of youth who have acquired HIV infection by diverse routes and at different ages. Many subjects in this study acquired HIV through MTCT (vertical) and had been receiving care at the sites since childhood, while others had sexually transmitted infections. Some subjects acquired infection via transfusion of infected blood products, and there was another group for whom the mode of transmission was unknown. Services dedicated to these youths must be prepared to manage patients who, although similar in age, have diverse medical and psychosocial needs.

In summary, pediatric sites in Latin America are following a diverse population of HIV-infected adolescents. Early diagnosis and linkage to care and treatment are critical for this population of youth, regardless of the mode of infection. This population has unsatisfactory levels of virologic suppression in response to ARV therapy, and the reasons for this need to be clarified and addressed. Additional research on effective interventions to improve adherence to ARV therapy is urgently needed. HIV pathogenesis and disease progression in the context of sexually acquired infection during adolescence are not fully understood and require further investigation. We hope this study from Latin America will increase awareness of the diversity of HIV-infected adolescents and will begin to contribute to the identification of important characteristics, problems and needs of youth living with HIV/AIDS around the world.

Funding

Eunice Kennedy Shriver National Institute of Child Health and Human Development Contracts #N01-HD-3-3345 and #N01-DK-8-0001.

Appendix 1

Principal investigators, co-principal investigators, study coordinators, data management center representatives, and NICHD staff (in the given order) include: Brazil: Belo Horizonte: Jorge Pinto, Flávia Faleiro (Universidade Federal de Minas Gerais); Caxias do Sul: Ricardo da Silva de Souza, Nicole Golin, Sílvia Mariani Costamilan (Universidade de Caxias do Sul/ Serviço Municipal de Infectologia); Nova Iguacu: Jose Pilotto, Beatriz Grinsztejn, Valdilea Veloso, Gisely Falco (Hospital Geral Nova de Iguacu—HIV Family Care Clinic); Porto Alegre: Ricardo da Silva de Souza, Breno Riegel Santos, Rita de Cassia Alves Lira (Universidade de Caxias do Sul/Hospital Conceição); Ricardo da Silva de Souza, Mario Ferreira Peixoto, Elizabete Teles (Universidade de Caxias do Sul/Hospital Fêmina); Ricardo da Silva de Souza, Marcelo Goldani, Margery Bohrer Zanetello (Universidade de Caxias do Sul /Hospital de Clínicas de Porto Alegre); Regis Kreitchmann, Debora Fernandes Coelho (Irmandade da Santa Casa de Misericordia de Porto Alegre); Ribeirão Preto: Marisa M. Mussi-Pinhata, Maria Célia Cervi, Márcia L. Isaac, Bento V. Moura Negrini (Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo); Rio de Janeiro: Ricardo Hugo S. Oliveira, Maria C. Chermont Sapia (Instituto de Puericultura e Pediatria Martagão Gesteira); Esau Custodio Joao, Maria Leticia Cruz, Plinio Tostes Berardo, Ezequias Martins (Hospital dos Servidores do Estado); São Paulo: Regina Celia de Menezes Succi, Daisy Maria Machado (Federal University of São Paulo); Marinella Della Negra, Wladimir Queiroz, Yu Ching Lian (Instituto de Infectologia Emilio Ribas); Mexico: Mexico City: Noris Pavía-Ruz, Patricia Villalobos-Acosta, Dulce Morales-Pérez (Hospital Infantil de México Federico Gómez); Peru: Lima: Jorge Alarcón Villaverde (Instituto de Medicina Tropical ‘Daniel Alcides Carrión’—Sección de Epidemiologia, UNMSM), Maria Castillo Díaz (Instituto Nacional de Salud del Niño), Mary Felissa Reyes Vega (Instituto de Medicina Tropical ‘Daniel Alcides Carrión’—Sección de Epidemiologia, UNMSM); Data Management and Statistical Center: Yolanda Bertucci, Laura Freimanis Hance, René Gonin, D. Robert Harris, Roslyn Hennessey, Margot Krauss, James Korelitz, Sharon Sothern de Sanchez, Sonia K. Stoszek (Westat, Rockville, MD, USA); NICHD: Rohan Hazra, Lynne Mofenson, Jennifer Read, George Siberry, Carol Worrell (Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland). Supported by NICHD Contract #HHSN267200800001 C (NICHD Control #N01-DK-8-0001).