Perioperative management of patients with congenital or acquired disorders of the QT interval.

QT prolongation can be attributable to various causes that can be categorised as acquired or congenital. Arrhythmias related to QT prolongation can result in clinical presentations, such as syncope and sudden cardiac death. The perioperative period presents a number of issues that may affect a patient's risk of developing polymorphic ventricular tachycardia or torsades de pointes. Although most patients may have an unremarkable perioperative course, some may have complications; this review article aims to help clinicians avoid potential complications, and to help them address treatment for perioperative issues that may occur.

Seasonal variation of acute toxoplasmic lymphadenopathy in the United States.

We describe the seasonal variation of acute toxoplasmosis in the United States. Acute toxoplasmic lymphadenopathy (ATL) can be a surrogate of acute toxoplasmosis in patients in whom the date of onset of lymphadenopathy matches the window of acute infection predicted by serological tests performed at a reference laboratory. We used the electronic database of the Palo Alto Medical Foundation Toxoplasma Serology Laboratory (PAMF-TSL) (1997-2011) to identify cases of ATL. We tested the uniformity of distribution of ATL cases per month, across the 12 calendar months, using circular statistics uniformity tests. We identified 112 consecutive cases of ATL. The distribution of cases was not uniform across the 12 calendar months. We observed the highest peak of cases in December and a second highest peak in September. Similar months were identified in patients with acute toxoplasmosis in rural areas in France. The results were similar when we performed weighted analyses, weighting for the total number of Toxoplasma gondii IgG tests performed per month in the PAMF-TSL laboratory. This is the largest study to date of the seasonal variation of ATL in the United States. Physicians should advise high-risk individuals to avoid risk factors associated with T. gondii infections especially around those months.

Seroprevalence and risk factors for human T-cell lymphotropic virus (HTLV-I) infection among ethnically and geographically diverse Peruvian women.

OBJECTIVE: To assess the seroprevalence and risk factors for HTLV-I infection in Peruvian women. METHODS: Five hundred and sixty-eight healthy women >20 years of age from three Peruvian regions were randomly selected and screened for HTLV-I. ELISA-reactive sera were confirmed via immunofluorescence assay, recombinant immunoblot assay, Western blot, and PCR. Women from Huanta (n=303), an Andean city inhabited by indigenous Quechuans, El Carmen (n=132), a primarily African-American coastal town, and Lima (n=133), with its Mestizo population, were selected. RESULTS: HTLV-I antibodies were present in 2.5% (14/568) of women (1.3% in Huanta, 3.8% in El Carmen, and 3.8% in Lima); 2.5%, 2.7% and 2.6% of Quechuans, Mestizas and African-Americans, respectively, were infected. History of a blood transfusion (P <0.00002), chronic scabies (P <0.02), having a relative with leukemia (P <0.04), age +/- 38 years (P <0.03), young age at first intercourse (P <0.04), lifetime partners >4 (P <0.04), educational status (P <0.02) and >4 pregnancies (P <0.03) were significantly associated with infection. CONCLUSIONS: HTLV-I is endemic among asymptomatic Peruvian women. Parenteral, vertical and heterosexual transmission are associated with infection.

No se golpea, no se lesiona, no se asesina. ¡Jamás! cuidados de urgencias en el maltrato a mujeres / Do not hit, injure or kill. Ever! Emergency care for woman abuse

En los últimos años ha habido un incremento de los malos tratos y agresiones físicas a las mujeres; ello hace necesario una agilización en el tratamiento social, médico y judicial de estas pacientes. Nuestro estudio describe y analiza los datos estadísticos de las mujeres maltratadas que fueron atendidas en el Centro de Urgencias y Especialidades Médicas del Ayuntamiento de Sevilla durante el año 2000 (AU)

Group A streptococcal meningitis: report of a case and review of literature since 1976.

Group A streptococcal (GAS) invasive disease has become increasingly common in recent years. However, acute bacterial meningitis caused by this pathogen is unusual. We report a case of GAS meningitis in a previously healthy 21/2-year-old child associated with a dramatically rapid course and fatal outcome. A literature review of previously reported cases is presented. This case serves as a reminder that GAS can cause severe meningitis in otherwise healthy hosts.

Immune responses to measles and mumps vaccination of infants at 6, 9, and 12 months.

Immunizing infants against measles at the youngest age possible has the potential to reduce morbidity and mortality. The ability of infants at 6, 9, or 12 months to respond to measles and mumps vaccines was evaluated by measuring T cell proliferation, interferon-gamma production, and neutralizing antibody titers before and after vaccination. Infants in all age groups had equivalent cellular immune responses to measles or mumps viruses, with or without passive antibodies when immunized. In contrast, 6-month-old infants without passive antibodies had low geometric mean titers of antibody to measles or mumps viruses and low seroconversion rates. Geometric mean titers of antibody to measles virus increased if infants were revaccinated at 12 months. Six-month-old infants had limited humoral responses to paramyxovirus vaccines, whereas cellular immunity was equivalent to that of older infants. T cell responses can be established by immunization with these live attenuated virus vaccines during the first year, despite the presence of passive antibodies.

Lack of definitive severe mitochondrial signs and symptoms among deceased HIV-uninfected and HIV-indeterminate children < or = 5 years of age, Pediatric Spectrum of HIV Disease project (PSD), USA.

BACKGROUND: In response to recent reports of mitochondrial dysfunction in HIV-uninfected infants exposed to antiretroviral (ARV) prophylaxis, the Perinatal Safety Review Working Group reviewed deaths in five large HIV-exposed perinatal cohorts in the United States to determine if similar cases of severe mitochondrial toxicity could be detected. We describe the results of this review for the PSD cohort. METHODS: Hospitalization, clinic and death records for deceased HIV-uninfected and HIV-indeterminate children who were less than 5 years of age were reviewed. Standard definitions were used to classify HIV infection status and the likelihood that signs and symptoms were related to mitochondrial dysfunction. Children were classified as having signs and symptoms that were considered (1) unrelated, (2) unlikely, (3) consistent with, or (4) likely related to mitochondrial disease. SIDS deaths were put into a separate category. RESULTS: 8,465 of 13,125 HIV-exposed children were either HIV-uninfected or HIV-indeterminate. Among the 84 deaths in the subgroup of 8,465 children, 9 were considered in Class 2 (unlikely), 4 were considered in Class 3 (consistent with), and none were considered in Class 4 (likely). 97% of those children who received ARV prophylaxis received zidovudine alone. None of the HIV-uninfected deaths were classified in 2, 3, or 4; and only one of these was exposed to ARV prophylaxis. Among the 3 HIV-indeterminate children who were classified in 3 (consistent with), 2 had no or unknown ARV exposure before 1994 when use of ZDV prophylaxis became the standard of care. Both HIV-uninfected and HIV-indeterminate children with ARV exposure or unknown exposure had lower mortality rates than children without ARV exposure. CONCLUSION: Monoprophylaxis with ZDV was not associated with higher death rates in the cohort of 8,465 children or with any findings likely consistent with mitochondrial dysfunction among the 85 deaths. Ongoing monitoring of drug safety in large multi-site prospective cohort studies of HIV-exposed children is essential in the era of highly active antiretroviral therapy.

Lessons learned from a review of the development of selected vaccines. National Vaccine Advisory Committee.

BACKGROUND: Although the vaccine research and development network in the United States remains vibrant, its continued success requires maintaining harmonious interaction among its many components. Changing one component is likely to affect the system overall. An examination of case studies of the development of selected vaccines would allow an examination of the network as a whole. This article presents conclusions drawn from the case study review undertaken. OBJECTIVE: Successful development of vaccines is a time-intensive process requiring years of commitment from a network of scientists and a continuum of regulatory and manufacturing entities. We undertook this work to shed light on how well the vaccine development system in the United States performs. METHOD: The National Vaccine Advisory Committee examined the research and development pathways of several vaccines that reached licensure expeditiously (hepatitis B vaccine, Haemophilus influenzae type b conjugate vaccines); some that became licensed only after considerable delay (oral typhoid Ty21a vaccine, varicella vaccine); some that are at the point of imminent or recent licensure (reassortant Rhesus rotavirus vaccine, which was licensed by the Food and Drug Administration on August 30, 1998) or near submission for licensure (intranasal cold adapted influenza vaccine); and one for which clinical development is slow because of hurdles that must be overcome (respiratory syncytial virus vaccines). RESULTS: Some common themes emerged from the reviews of these vaccine "case histories": the expediting influence of a strong scientific base and rationale; the need for firm quantitation of disease burden and clear identification of target populations; the critical role played by individuals or teams who act as "champions" to overcome the inevitable obstacles; availability of relevant animal models, high-quality reagents and standardized assays to measure immune response; the absolute requirement for well designed, meticulously executed clinical trials of vaccine safety, immunogenicity, and efficacy; postlicensure measurements of the public health impact of the vaccine and a track record of the vaccine's safety and acceptance with large-scale use; and the critical need for international collaborations to evaluate vaccines against diseases of global importance that are rare in the United States (eg, typhoid fever). It was clear that the critical step-up from bench scale to pilot lots and then to large-scale production, which depends on a small group of highly trained individuals, is often a particularly vulnerable point in the development process. CONCLUSIONS: One fundamental lesson learned is that within the varied and comprehensive US vaccine development infrastructure, multiple and rather distinct paths can be followed to reach vaccine licensure. The National Vaccine Advisory Committee review process should be conducted periodically in the future to ascertain that the US vaccine development network, which has been enormously productive heretofore and has played a leadership role globally, is adapting appropriately to ensure that new, safe, and efficacious vaccines become available in a timely manner.

The epidemiology of neonatal herpes simplex virus infections in California from 1985 to 1995.

Comprehensive hospital discharge data completed by the California Office of Statewide Health Planning and Development was used to determine whether the proportion of infants

IL-12, IFN-gamma, and T cell proliferation to measles in immunized infants.

Measles infection in infants is associated with severe complications, and secondary infections are attributed to generalized immunosuppression. Measles binding to its monocyte receptor down-regulates IL-12 which is expected to diminish Th1-like cytokine responses, including IFN-gamma. Whether young infants can be immunized effectively against measles is an important public health issue. We evaluated Ag-specific IL-12, IFN-gamma, and T cell responses of infants at 6 (n = 60), 9 (n = 46), or 12 mo (n = 56) of age and 29 vaccinated adults. IL-12 and IFN-gamma release by PBMC stimulated with measles Ag increased significantly after measles immunization in infants. IL-12 and IFN-gamma concentrations were equivalent in younger and older infants, but IL-12 concentrations were significantly lower in infants than in adults (p = 0.04). IL-12 production by monocytes was down-regulated by measles; the addition of recombinant human IL-12 enhanced IFN-gamma production by PBMC stimulated with measles Ag, but infant T cells released significantly less IFN-gamma than adult T cells under this condition. Of particular interest, the presence of passive Abs to measles had no effect on the specific T cell proliferation or IFN-gamma production after measles stimulation. Cellular immunity to measles infection and vaccination may be limited in infants compared with adults as a result of less effective IFN-gamma and IL-12 production in response to measles Ags. These effects were not exaggerated in younger infants compared with effects in infants who were immunized at 12 mo. In summary, infant T cells were primed with measles Ag despite the presence of passive Abs, but their adaptive immune responses were limited compared with those of adults.

Serum level of maternal human immunodeficiency virus (HIV) RNA, infant mortality, and vertical transmission of HIV in Zimbabwe.

Maternal human immunodeficiency virus (HIV) RNA load, vertical transmission of subtype C HIV, and infant mortality were examined in 251 HIV-seropositive women and their infants in Zimbabwe. Demographic characteristics, health and medical histories, serum HIV RNA loads, and CD4+ lymphocyte counts for mothers were examined by logistic regression analysis to determine significant risk factors and their odds ratios for transmission and infant mortality. Tenfold (1 log10) incremental increases in maternal HIV RNA were associated with a 1.9-fold increase (95% confidence interval [CI], 1.2-2.9) in transmission and a 2.1-fold increase (95% CI, 1.3-3.5) in infant mortality (P<.01). Maternal CD4 cell counts and demographic and medical characteristics were not significant predictors of transmission. However, maternal CD4 cell counts below the median (400/mm3) were significantly associated with infant mortality (P=. 035, Fisher's exact test). The maternal level of serum HIV is an important determinant of vertical transmission and infant mortality in subtype C infection in Zimbabwe.

Patterns of health seeking behavior during episodes of childhood diarrhea: a study of Tzotzil-speaking Mayans in the highlands of Chiapas, Mexico.

In Chiapas, Mexico, diarrheal disease causes the majority of all deaths in children under the age of five. Treatment of childhood diarrhea may be influenced by local beliefs and cultural practices. Few studies have attempted to quantitatively evaluate health seeking behavior (HSB) for diarrheal diseases in indigenous communities, while controlling for potential confounding factors such as parental education or socioeconomic status. A rapid ethnographic survey was conducted in Nabenchauc, Chiapas, to determine hypothetical HSB patterns for each of four major types of childhood diarrhea. Additionally, we examined the actual HSB for the last episode of childhood diarrheal illness within the household. One hundred households participated in the survey; 94 households with children < 5 years old reported a mean of 1.9 diarrheal episodes during the preceding month. Households reported using a mean of 1.3 types of in-home remedies. Oral rehydration therapy (ORT) was used in <2% of the 368 HSB patterns elicited for the four types of diarrhea. HSB patterns utilized an eclectic combination of traditional, allopathic, local and distant health care options. A mean of 2.5 outside-the-home health care options were reported for each diarrheal type; the local grocery store was reported in 245 (67%) of the hypothetical HSB patterns and as a first option in 199 (54%). Maternal and/or paternal education had little impact on hypothetical HSB. Households with lower SES were more likely to report using local grocery stores as a first option and were less likely to use options outside the village. The rapid ethnographic survey approach allows for assessment of changes in the approach to health care option utilization in cultures incorporating new health care paradigms. Public health interventions targeting local stores may lead to increased use of ORT, thereby potentially reducing early morbidity and mortality due to childhood diarrhea.

Extremely high levels of alkaline phosphatase in hospitalized patients.

We determined the diseases associated with extremely high levels of alkaline phosphatase in hospitalized patients. Computerized laboratory records of the Hospital of Saint Raphael identified all inpatients who had elevations of alkaline phosphatase above 1,000 U/l from April 1994 to September 1995. Thirty-seven inpatients with alkaline phosphatase levels above 1,000 U/l were identified. Six had bone involvement from malignancy or Paget's disease and were eliminated from further analysis, and 31 patients were included in the study. Levels of alkaline phosphatase ranged from 1,014 to 3,360 U/l. Ten patients had sepsis as the cause of the elevated alkaline phosphatase. These included gram-negative organisms, gram-positive organisms, and two patients with fungal sepsis. Seven of 10 patients with sepsis had an extremely high alkaline phosphatase level and a normal bilirubin, 3 of 10 patients with sepsis also had acquired immunodeficiency syndrome (AIDS). Eight patients had biliary obstruction, 7 with malignant obstruction and 1 with a common bile duct stone. Nine patients had AIDS. The cause of the elevated alkaline phosphatase in these included three with sepsis, three with mycobacterium avium intracellulare (MAI) infection, two with cytomegalovirus infection, and one with Dilantin toxicity. Three patients had diffuse liver metastases. Finally, four patients had benign intrahepatic disease, including one patient with liver hemangiomas, one patient with sarcoid hepatitis, one patient with lead toxicity, and one patient with drug-induced cholestasis. Extremely high elevations of alkaline phosphatase are most frequently seen in patients with sepsis, malignant obstruction, and AIDS. Patients with sepsis can have an extremely high alkaline phosphatase level and a normal bilirubin. A variety of other causes were also noted.

Population-based prevalence of symptomatic and asymptomatic astrovirus infection in rural Mayan infants.

Symptomatic and asymptomatic astrovirus infection was prospectively determined in a 3-year birth cohort of Mayan infants. Stool samples from 271 infants and 268 older siblings were tested for astrovirus, adenovirus 40/41, rotavirus and Salmonella, Shigella and Campylobacter species. Concurrent diarrhea, vomiting, fever, or anorexia were noted. Astrovirus was detected in 164 infants (61%) and 20 siblings (7%). Rotavirus (4%) and adenovirus 40/41 (13%) were isolated less frequently. Of all diarrheal episodes reported at a visit, 26% (78/305) were associated with astrovirus; 17% (78/452) of astrovirus infections were associated with diarrhea and 9% with other symptoms. Only diarrhea was associated with astrovirus infection (odds ratio, 1.4; 95% confidence interval [CI], 1.07-1.92; P = .01). Of infants with astrovirus, 70% shed at multiple visits over a period of 2-17 weeks (median, 5). The point prevalence of astrovirus infection was significantly higher among infants than siblings (relative risk, 6.18; 95% CI, 3.93-9.72; P < .0001, chi2). Astrovirus was identified throughout the year, peaked in March and May, and decreased in September. In this population, astrovirus was the most common enteric pathogen isolated; symptomatic infection was prevalent among infants.

Deficiency of the humoral immune response to measles vaccine in infants immunized at age 6 months.

CONTEXT: Measles causes serious morbidity in infants, with the highest risk among those who are 6 to 12 months of age. In the United States, measles vaccine has been given at age 12 to 15 months to minimize interference by passive antibodies and to achieve the high seroprevalence required for herd immunity. Infants of mothers with vaccine-induced immunity may lose passively acquired antibodies before 12 months, leaving them susceptible to measles infection. OBJECTIVE: To assess the immunogenicity of measles vaccine in infants younger than 12 months. DESIGN: Cohort study conducted before and after measles immunization. SETTING: Pediatric clinic in Palo Alto, Calif. PARTICIPANTS: Infants 6 (n = 27), 9 (n = 26), and 12 (n = 34) months of age were enrolled; 72 provided both initial and follow-up samples. MAIN OUTCOME MEASURES: Evaluation of immunogenicity before and 12 weeks after measles vaccination, including measles neutralizing antibody titers, measles-specific T-cell proliferation, and cytokine profiles. RESULTS: Measles neutralizing antibodies were present before vaccination in 52% (12/23), 35% (7/20), and 0% (0/22) of 6-, 9-, and 12-month-old infants, respectively. In the absence of detectable passive antibodies, geometric mean titers after vaccination were significantly lower in 6-month-old infants compared with 9-month-old infants (27 vs 578, P = .01) and 12-month-old infants (27 vs 972, P=.001). The seroconversion rate, defined as a 4-fold rise in antibody titer, in these 6-month-old infants was only 67%, and only 36% of these infants achieved seroprotective neutralizing antibody titers of 120 or higher after vaccination compared with 100% of 9- and 12-month-old infants lacking detectable passive antibody prior to vaccination. T-cell proliferation and cytokine responses to measles did not differ with age. CONCLUSIONS: Humoral immunity was deficient in 6-month-old infants given measles vaccine, even in the absence of detectable passively acquired neutralizing antibodies. Comparison of their responses with those of 9- and 12-month-old infants indicates that a developmental maturation of the immune response to measles may occur during the first year of life, which affects the immunogenicity of measles vaccine.

Mortality in the first 2 years among infants born to human immunodeficiency virus-infected women in Harare, Zimbabwe.

Transmission of human immunodeficiency virus (HIV) and mortality was studied among infants of infected women in Zimbabwe. Of 367 infants born to HIV-infected women, 72 (19.6%) died compared with 20 (5.4%) of 372 infants of uninfected women (P < .01). Infection by HIV DNA polymerase chain reaction among infants who survived >7 days and died within 2 years could be assessed in 87% (58/67) of infants of infected women and 83% (5/6) of infants of uninfected women; transmission occurred in 40 of 58 infants. Among 27 infected infants tested at birth, 19 (70%), 5 (19%), and 3 (11%) were apparently infected via in utero, intrapartum or early postpartum, and late postpartum transmission, respectively. The majority of HIV-infected infants who died in the first 2 years of life were likely to have acquired in utero infection.

Pneumocystis carinii pneumonia prophylaxis and early clinical manifestations of severe perinatal human immunodeficiency virus type 1 infection. Northern California Pediatric HIV Consortium.

BACKGROUND: Some children with perinatal HIV infection develop early progression to severe symptoms (Category C) within the first 4 years of life. Prophylactic therapy with trimethoprim-sulfamethoxazole (TMP/SMX) may affect progression by decreasing the incidence of Pneumocystis carinii pneumonia (PCP). METHODS: HIV progression to Category C in the first 3 years of life was retrospectively analyzed in a population-based cohort of children with perinatal HIV infection followed for > or = 3 years from birth. Time to development of Category C and clinical patterns of new Category C diagnoses were examined in relation to patterns of PCP prophylaxis before diagnosis. RESULTS: Fifty-eight of 147 children developed 67 initial category C diseases by 3 years of age: PCP (n=24), encephalopathy (n=22), other opportunistic infections (n=19) and wasting (n=2). Before diagnosis therapy included TMP/ SMX and zidovudine (ZDV) (n=11), TMP/SMX alone (n=7), ZDV alone (n=1) and neither (n= 39). The probability of developing a Category C diagnosis after 2 years was significantly lower among children who received TMP/SMX compared with those who did not (29%, TMP/SMX vs. 45%, no TMP/SMX; 30%, TMP and ZDV vs. 45%, no therapy; P < 0.01). The frequency of PCP was significantly lower and that of HIV encephalopathy was significantly higher among children receiving TMP/SMX +/- ZDV before Category C diagnosis than among children receiving neither. CONCLUSION: In this study PCP prophylaxis was associated with longer time to Category C diagnoses in the first 3 years of life. This association was related to a decreased incidence of PCP and an increased incidence of encephalopathy as the first Category C diagnosis among children who received TMP/SMX.

Neutrophil CD11b expression as a diagnostic marker for early-onset neonatal infection.

OBJECTIVES: To determine whether neutrophil surface expression of CD11b predicts early-onset infection or suspected infection in at-risk infants. STUDY DESIGN: CD11b expression on peripheral blood neutrophils was determined by flow cytometry of whole blood samples. Blood (0.1 ml) was obtained from a convenience sample of at-risk infants admitted to the neonatal intensive care unit, stained with antibodies detecting CD11b and CD15, chilled, and analyzed within 8 hours. Blood for culture, blood counts, and C-reactive protein (CRP) determination was obtained simultaneously. Subjects were grouped on the basis of culture results and clinical signs, and investigators were blinded to CD11b level. RESULTS: Of 106 subjects, seven had positive bacterial or viral cultures ("confirmed infection"), 17 had clinical signs of infection but negative cultures ("suspected infection"), and 82 had negative cultures and no clinical signs ("no infection"). Neutrophil CD11b was elevated in all infants with confirmed infection, 94% with suspected infection, and none with no infection. The negative and positive predictive values, sensitivity, and specificity were 100%, 99%, 96%, and 100%, respectively, for diagnosis of neonatal infection at initial evaluation. CD11b levels correlated with peak CRP (r2 = 0.76, p < 0.0001); however, CD11b was elevated at the time of admission in all five infants with proven bacterial infection, whereas CRP was normal until the second day in the neonatal intensive care unit in three of these five. Both infants with positive viral cultures had elevated CD11b, but the CRP levels remained within normal limits. The negative predictive value of neutrophil CD11b for identifying suspected or confirmed infection was 99%. CONCLUSION: This assay for neutrophil CD11b is a promising test for exclusion of early-onset neonatal infection. If validated prospectively, this assay may reduce hospital and antibiotic use in the population of neonates at risk for early-onset infection.

Development of chemiluminescent probe hybridization, RT-PCR and nucleic acid cycle sequencing assays of Sabin type 3 isolates to identify base pair 472 Sabin type 3 mutants associated with vaccine associated paralytic poliomyelitis.

Sabin type 3 polio vaccine virus is the most common cause of poliovaccine associated paralytic poliomyelitis. Vaccine associated paralytic poliomyelitis cases have been associated with Sabin type 3 revertants containing a single U to C substitution at bp 472 of Sabin type 3. A rapid method of identification of Sabin type 3 bp 472 mutants is described. An enterovirus group-specific probe for use in a chemiluminescent dot blot hybridization assay was developed to identify enterovirus positive viral lysates. A reverse transcription-polymerase chain reaction (RT-PCR) assay producing a 319 bp PCR product containing the Sabin type 3 bp 472 mutation site was then employed to identify Sabin type 3 isolates. Chemiluminescent nucleic acid cycle sequencing of the purified 319 bp PCR product was then employed to identify nucleic acid sequences at bp 472. The enterovirus group probe hybridization procedure and isolation of the Sabin type 3 PCR product were highly sensitive and specific; nucleic acid cycle sequencing corresponded to the known sequence of stock Sabin type 3 isolates. These methods will be used to identify the Sabin type 3 reversion rate from sequential stool samples of infants obtained after the first and second doses of oral poliovirus vaccine.

Host and viral factors affecting the decreased immunogenicity of Sabin type 3 vaccine after administration of trivalent oral polio vaccine to rural Mayan children.

Factors affecting immunogenicity of the first 2 doses of oral poliovirus vaccine (OPV) among unimmunized Mayan infants were prospectively evaluated. The relative impact of multiple variables, including mass or routine vaccination, concurrent enteric bacterial (salmonella, shigella, and campylobacter) and viral (adenovirus 40/41, astrovirus, nonpolio enteroviruses, and rotavirus) infections, interference among Sabin vaccine viruses, and preexisting poliovirus antibodies were studied. Sera were available from 181 infants after 2 OPV doses. Seroresponses were 86% to Sabin type 1, 97% to Sabin type 2, and 61% to Sabin type 3 vaccines. Mass versus routine vaccination and preexisting poliovirus antibodies did not affect immunogenicity. By multiple logistic regression analysis, fecal shedding of homologous Sabin strains was associated with increased seroresponses to all Sabin types, especially to Sabin type 3. Decreased OPV immunogenicity was primarily attributable to interference of Sabin type 3 by Sabin type 2. OPV formulations with higher doses of Sabin type 3 could improve immunogenicity among infants in developing countries.