Performance of a household tuberculosis exposure survey among children in a Latin American setting

Treatment of Infection as a Core Strategy to Prevent Rifampicin-Resistant/Multidrug-Resistant Tuberculosis

An estimated 19 million people are infected with rifampicin-resistant/multidrug-resistant strains of tuberculosis worldwide. There is little done to prevent these individuals from becoming sick with RR/MDR-TB, a disease that is associated with high rates of morbidity, mortality, and suffering. There are multiple phase III trials currently being conducted to assess the effectiveness of treatment of infection (i.e., "preventive therapy") for RR/MDR-TB, but their results are likely years away. In the meantime, there is sufficient evidence to support a more comprehensive management of people who have been exposed to RR/MDR-TB so that they can maintain their health. We present a patient scenario and share our experience in implementing a systematic post-exposure management program in South Africa with the goal of inspiring similar programs in other high-burden RR/MDR-TB settings.

Predicting Vibrio cholerae infection and symptomatic disease: a systems serology study

BACKGROUND

Vibriocidal antibodies are currently the best characterised correlate of protection against cholera and are used to gauge immunogenicity in vaccine trials. Although other circulating antibody responses have been associated with a decreased risk of infection, the correlates of protection against cholera have not been comprehensively compared. We aimed to analyse antibody-mediated correlates of protection from both V cholerae infection and cholera-related diarrhoea.

METHODS

We conducted a systems serology study that analysed 58 serum antibody biomarkers as correlates of protection against V cholerae O1 infection or diarrhoea. We used serum samples from two cohorts: household contacts of people with confirmed cholera in Dhaka, Bangladesh, and cholera-naive volunteers who were recruited at three centres in the USA, vaccinated with a single dose of CVD 103-HgR live oral cholera vaccine, and then challenged with V cholerae O1 El Tor Inaba strain N16961. We measured antigen-specific immunoglobulin responses against antigens using a customised Luminex assay and used conditional random forest models to examine which baseline biomarkers were most important for classifying individuals who went on to develop infection versus those who remained uninfected or asymptomatic. V cholerae infection was defined as having a positive stool culture result on days 2-7 or day 30 after enrolment of the household's index cholera case and, in the vaccine challenge cohort, was the development of symptomatic diarrhoea (defined as two or more loose stools of ≥200 mL each, or a single loose stool of ≥300 mL over a 48-h period).

FINDINGS

In the household contact cohort (261 participants from 180 households), 20 (34%) of the 58 studied biomarkers were associated with protection against V cholerae infection. We identified serum antibody-dependent complement deposition targeting the O1 antigen as the most predictive correlate of protection from infection in the household contacts, whereas vibriocidal antibody titres ranked lower. A five-biomarker model predicted protection from V cholerae infection with a cross-validated area under the curve (cvAUC) of 79% (95% CI 73-85). This model also predicted protection against diarrhoea in unvaccinated volunteers challenged with V cholerae O1 after vaccination (n=67; area under the curve [AUC] 77%, 95% CI 64-90). Although a different five-biomarker model best predicted protection from the development of cholera diarrhoea in the challenged vaccinees (cvAUC 78%, 95% CI 66-91), this model did poorly at predicting protection against infection in the household contacts (AUC 60%, 52-67).

INTERPRETATION

Several biomarkers predict protection better than vibriocidal titres. A model based on protection against infection among household contacts was predictive of protection against both infection and diarrhoeal illness in challenged vaccinees, suggesting that models based on observed conditions in a cholera-endemic population might be more likely to identify broadly applicable correlates of protection than models trained on single experimental settings.

FUNDING

National Institute of Allergy and Infectious Diseases and National Institute of Child Health and Human Development, National Institutes of Health.

Is exclusive breastfeeding for six-months protective against pediatric tuberculosis?

Experts recommend exclusive breastfeeding from birth to six months because it protects against deadly childhood illness, including respiratory tract infections and diarrhea. We hypothesized that exclusive breastfeeding would decrease the risk of active tuberculosis (TB) in children. We analyzed cross-sectional data from 279 children in Lima, Peru aged 6 to 59 months with TB symptoms and a close adult contact with TB. Mothers self-reported breastfeeding, and children were evaluated for TB per national guidelines. To quantify the association between exclusive breastfeeding and TB, we estimated prevalence ratios using a generalized linear model with a log link, binomial distribution, and robust variance. Twenty-two percent of children were diagnosed with TB and 72% were exclusively breastfed for six months. We found no evidence that six months of exclusive breastfeeding was associated with TB disease in either bivariate analyses (prevalence ratio [PR] = 1.5; 95%CI = 0.8–2.5) or multivariable analyses adjusting for sex and socioeconomic status (adjusted PR = 1.6; 95%[CI] = 0.9–2.7). In post hoc analyses among children whose close TB contact was their mother, we found evidence of a weak positive association between breastfeeding and TB (aPR = 2.1; 95%[CI] = 0.9–4.9). This association was not apparent among children whose close contact was not the mother (aPR = 1.2; 95%[CI] = 0.6–2.4). Our results raise the possibility that children who are breastfed by mothers with TB may be at increased risk for TB, given the close contact. Due to the cross-sectional study design, these results should be interpreted with caution. If these findings are confirmed in longitudinal analyses, future interventions could aim to minimize TB transmission from mothers with TB to breastfeeding infants.

Quantified TB Exposure Can Predict Prevalent TB Disease in Child Contacts

In a matched case-control study in Pakistan, we found that quantified tuberculosis (TB) exposure using a 10-point score is associated with prevalent TB disease in pediatric household contacts. A 1 unit increase in TB exposure score increased the odds of TB disease by 44% (conditional odds ratio: 1.44, 95% confidence interval: 1.33-1.56). Collecting well-documented exposure history can help TB diagnosis in resource-limited settings.

Uncovering reasons for treatment initiation delays among children with TB in Lima, Peru

BACKGROUND: Timely diagnosis and treatment of pediatric tuberculosis (TB) is critical to reducing mortality but remains challenging in the absence of adequate diagnostic tools. Even once a TB diagnosis is made, delays in treatment initiation are common, but for reasons that are not well understood.METHODS: To examine reasons for delay post-diagnosis, we conducted semi-structured interviews with Ministry of Health (MoH) physicians and field workers affiliated with a pediatric TB diagnostic study, and caregivers of children aged 0-14 years who were diagnosed with pulmonary TB in Lima, Peru. Interviews were analyzed using systematic comparative and descriptive content analysis.RESULTS: We interviewed five physicians, five field workers and 26 caregivers with children who initiated TB treatment < 7 days after diagnosis (n = 15) or who experienced a delay of ≥7 days (n = 11). Median time in delay from diagnosis to treatment initiation was 26 days (range 7-117). Reasons for delay included: health systems challenges (administrative hurdles, medication stock, clinic hours), burden of care on families and caregiver perceptions of disease severity.CONCLUSION: Reasons for delay in treatment initiation are complex. Interventions to streamline administrative processes and tools to identify and support families at risk for delays in treatment initiation are urgently needed.

Incident Tuberculosis Diagnoses in Children at High Risk for Disease

We followed 35 children meeting a research definition for unconfirmed tuberculosis (TB) but in whom a pediatric pulmonologist did not diagnose or treat TB. After a median follow-up of 16.4 months, most children were not diagnosed with TB following a comprehensive evaluation. However, 2 were diagnosed with TB, demonstrating high TB risk (6%; exact 95% CI, 1%–19%). In some contexts, researchers may wish to supplement these research definitions with clinical decision data and longitudinal follow-up in order to improve specificity.

Design and Evaluation of Risk Assessment Tools to Identify Pediatric Tuberculosis Infection in Bohol, the Philippines, a Low-HIV- and High-TB-Burden Setting

Identifying children with, or at substantial risk of, Mycobacterium tuberculosis infection (TBI) and providing TB preventive therapy (TPT) represent an important, yet challenging, strategy in curbing the global burden of childhood TB. Risk assessment scoring tools, which quantify risks associated with unique factors characterizing an individual, could act as a surrogate measure of TBI risk and guide effective and efficient TPT delivery. We assessed important risk factors of childhood TBI and created risk assessment tools through secondary analysis of data from a large, community-based childhood TB prevalence study in the island province of Bohol in the Philippines, a low–HIV- and high–TB-burden, post-disaster setting. We identified four factors that were statistically associated with acquiring TBI—being 5 years or older, having a known TB contact, having a known TB contact who was either the mother or another primary caregiver, and living in a high–TB-burden municipality. We created 2-item, 4-item, and 9-item scores intended to identify child TBI in this low-resource, low–HIV-, and high–TB-burden setting. In addition to the design, evaluation, and impact analysis of these generalizable and valuable risk assessment tools, our study findings emphasize the necessity of targeting both household and community-associated transmissions of childhood TBI to achieve the global goal to end TB.