Background: Childhood growth is a cornerstone of pediatric research. Statistical models need to consider individual trajectories to adequately describe growth outcomes. Specifically, well-defined longitudinal models are essential to characterize both population and subject-specific growth. Linear mixed-effect models with cubic regression splines can account for the nonlinearity of growth curves and provide reasonable estimators of population and subject-specific growth, velocity and acceleration. Methods: We provide a stepwise approach that builds from simple to complex models, and account for the intrinsic complexity of the data. We start with standard cubic splines regression models and build up to a model that includes subject-specific random intercepts and slopes and residual autocorrelation. We then compared cubic regression splines vis-à-vis linear piecewise splines, and with varying number of knots and positions. Statistical code is provided to ensure reproducibility and improve dissemination of methods. Models are applied to longitudinal height measurements in a cohort of 215 Peruvian children followed from birth until their fourth year of life. Results: Unexplained variability, as measured by the variance of the regression model, was reduced from 7.34 when using ordinary least squares to 0.81 (p < 0.001) when using a linear mixed-effect models with random slopes and a first order continuous autoregressive error term. There was substantial heterogeneity in both the intercept (p < 0.001) and slopes (p < 0.001) of the individual growth trajectories. We also identified important serial correlation within the structure of the data (ρ = 0.66; 95 % CI 0.64 to 0.68; p < 0.001), which we modeled with a first order continuous autoregressive error term as evidenced by the variogram of the residuals and by a lack of association among residuals. The final model provides a parametric linear regression equation for both estimation and prediction of population- and individual-level growth in height. We show that cubic regression splines are superior to linear regression splines for the case of a small number of knots in both estimation and prediction with the full linear mixed effect model (AIC 19,352 vs. 19,598, respectively). While the regression parameters are more complex to interpret in the former, we argue that inference for any problem depends more on the estimated curve or differences in curves rather than the coefficients. Moreover, use of cubic regression splines provides biological meaningful growth velocity and acceleration curves despite increased complexity in coefficient interpretation. Conclusions: Through this stepwise approach, we provide a set of tools to model longitudinal childhood data for non-statisticians using linear mixed-effect models.

Maternal immunization has the potential to reduce both maternal and infant morbidity and mortality by protecting women from complications during pregnancy as well as conferring protection for babies who are too young to be vaccinated. Limited evidence is available about the drivers of maternal immunization in middle-income countries such as Peru. Vaccines against tetanus, diphtheria and influenza are recommended beginning in the second trimester in Peru; however, vaccination coverage has remained low in Peru compared to other countries in the region. As additional vaccines are recommended for administration in pregnancy, a better understanding of the perceptions and attitudes of pregnant women that influence vaccination are needed to design communication materials. We conducted an exploratory qualitative study to understand the individual level factors influencing pregnant women's vaccine uptake. We interviewed pregnant women about their knowledge, perceptions and experiences with vaccination during pregnancy. Community health workers recruited women in a peri urban area of Peru in April 2018. Twelve women were interviewed, the majority of which had received vaccination during the current pregnancy. The most common reasons for vaccination were to protect the baby and because vaccines are effective. Concerns included vaccine safety during pregnancy and adverse effects on the unborn baby. Some women mentioned that because vaccines are given later in pregnancy, the unborn baby is stronger, so vaccines will not harm them. Women highlighted that the main reason for not being vaccinated was lack of information. They also noted that they were the decision-maker in whether or not they were vaccinated. Most women said that they trusted healthcare providers and that trust was linked to providing information through open communication. Overall, participants were supportive of maternal vaccination. They believed that vaccines were effective in protecting both their unborn baby and themselves. The main reason given for non-vaccination was lack of knowledge about vaccination in pregnancy. The strong desire expressed by study participants to get more information presents an opportunity for immunization programs to develop interventions that facilitate better information dissemination to pregnant women to increase vaccination uptake.

Background: A recent study found lower self-reported prevalence of tobacco smoking in a peri-urban area of Lima, Peru than previously reported in urban samples. These regions encompass substantial proportions of Peru’s population – ones at greater risk of disease due to reduced healthcare...

Trypanosoma cruzi infection leads to Chagas disease (CD), a neglected tropical infection of significant public health importance in South and Central America and other, non-endemic, countries. Pregnant women and their children are of particular importance to screen as T. cruzi can be transmitted vertically. The objective of this study was to screen for T. cruzi infection among pregnant women from endemic areas seen at the Hospital General de Mexico for prenatal care, so that they and their children may be quickly connected to CD treatment. Pregnant women were recruited through the hospital prenatal clinic and screened for T. cruzi infection using a series of serological and molecular tests. Of 150 screened patients, mean age 26.8 (SD 6.4), 30 (20.0%) were positive by at least one diagnostic test. Of these, only nine (6%) were positive as determined by PCR. Diagnosis of chronic CD is difficult in endemic places like Mexico due to the limitations of current commercially available diagnostic tests. Further evaluation of diagnostic performance of various assays could improve current CD diagnostic algorithms and proper care management in these regions. Genetic variability in the parasite may also play a role in the differing assay performances seen in this study, and this may be a valuable avenue of further research.

: As many as one in three people worldwide have anemia, with young children at increased risk of both disease and complications. In settings without clinical laboratories, portable hemoglobinometers serve important roles in diagnosing anemia and estimating prevalence. Here, we assess the validity of two such point-of-care devices—the HemoCue Hb201 and the HemoCue Hb301—relative to the international reference standard, the cyanmethemoglobin method. In total, 428 children ages 6–60 months were recruited at health posts in Lima, Peru, and venous and capillary blood samples were collected from each participant. Venous blood was assessed with the cyanmethemoglobin method, whereas capillary blood was assessed using the Hb201 and the Hb301; 16.1% of participants were found to have anemia using the cyanmethemoglobin method. Both the Hb201 (43.7%) and the Hb301 (20.6%) overestimated this prevalence, with the former reaching statistical significance (P <0.0001 and P = 0.11, respectively). Both devices also tended to underestimate hemoglobin concentration, with the Hb201 (mean difference = −0.99 g/dL; percentage error = −8.1%) being appreciably less accurate than the Hb301 (mean difference = −0.35 g/dL; percentage error = −2.7%). Areas under the curve for the Hb201 (0.92) and the Hb301 (0.93) were statistically similar (P = 0.28); however, the Hb201 incorrectly classified 29.4% of participants compared with 11.0% for the Hb301. Both devices had more false positives than false negatives. In conclusion, the Hb301 was found to be significantly more accurate than the Hb201 at measuring hemoglobin, diagnosing anemia, and estimating anemia prevalence.