Xpert MTB/RIF Ultra assay for tuberculosis disease and rifampicin resistance in children

BACKGROUND

Every year, an estimated one million children and young adolescents become ill with tuberculosis, and around 226,000 of those children die. Xpert MTB/RIF Ultra (Xpert Ultra) is a molecular World Health Organization (WHO)-recommended rapid diagnostic test that simultaneously detects Mycobacterium tuberculosis complex and rifampicin resistance. We previously published a Cochrane Review 'Xpert MTB/RIF and Xpert MTB/RIF Ultra assays for tuberculosis disease and rifampicin resistance in children'. The current review updates evidence on the diagnostic accuracy of Xpert Ultra in children presumed to have tuberculosis disease. Parts of this review update informed the 2022 WHO updated guidance on management of tuberculosis in children and adolescents.

OBJECTIVES

To assess the diagnostic accuracy of Xpert Ultra for detecting: pulmonary tuberculosis, tuberculous meningitis, lymph node tuberculosis, and rifampicin resistance, in children with presumed tuberculosis. Secondary objectives To investigate potential sources of heterogeneity in accuracy estimates. For detection of tuberculosis, we considered age, comorbidity (HIV, severe pneumonia, and severe malnutrition), and specimen type as potential sources. To summarize the frequency of Xpert Ultra trace results.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register, MEDLINE, Embase, three other databases, and three trial registers without language restrictions to 9 March 2021.

SELECTION CRITERIA

Cross-sectional and cohort studies and randomized trials that evaluated Xpert Ultra in HIV-positive and HIV-negative children under 15 years of age. We included ongoing studies that helped us address the review objectives. We included studies evaluating sputum, gastric, stool, or nasopharyngeal specimens (pulmonary tuberculosis), cerebrospinal fluid (tuberculous meningitis), and fine needle aspirate or surgical biopsy tissue (lymph node tuberculosis). For detecting tuberculosis, reference standards were microbiological (culture) or composite reference standard; for stool, we also included Xpert Ultra performed on a routine respiratory specimen. For detecting rifampicin resistance, reference standards were drug susceptibility testing or MTBDRplus.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and, using QUADAS-2, assessed methodological quality judging risk of bias separately for each target condition and reference standard. For each target condition, we used the bivariate model to estimate summary sensitivity and specificity with 95% confidence intervals (CIs). We stratified all analyses by type of reference standard. We summarized the frequency of Xpert Ultra trace results; trace represents detection of a very low quantity of Mycobacterium tuberculosis DNA. We assessed certainty of evidence using GRADE.

MAIN RESULTS

We identified 14 studies (11 new studies since the previous review). For detection of pulmonary tuberculosis, 335 data sets (25,937 participants) were available for analysis. We did not identify any studies that evaluated Xpert Ultra accuracy for tuberculous meningitis or lymph node tuberculosis. Three studies evaluated Xpert Ultra for detection of rifampicin resistance. Ten studies (71%) took place in countries with a high tuberculosis burden based on WHO classification. Overall, risk of bias was low. Detection of pulmonary tuberculosis Sputum, 5 studies Xpert Ultra summary sensitivity verified by culture was 75.3% (95% CI 64.3 to 83.8; 127 participants; high-certainty evidence), and specificity was 97.1% (95% CI 94.7 to 98.5; 1054 participants; high-certainty evidence). Gastric aspirate, 7 studies Xpert Ultra summary sensitivity verified by culture was 70.4% (95% CI 53.9 to 82.9; 120 participants; moderate-certainty evidence), and specificity was 94.1% (95% CI 84.8 to 97.8; 870 participants; moderate-certainty evidence). Stool, 6 studies Xpert Ultra summary sensitivity verified by culture was 56.1% (95% CI 39.1 to 71.7; 200 participants; moderate-certainty evidence), and specificity was 98.0% (95% CI 93.3 to 99.4; 1232 participants; high certainty-evidence). Nasopharyngeal aspirate, 4 studies Xpert Ultra summary sensitivity verified by culture was 43.7% (95% CI 26.7 to 62.2; 46 participants; very low-certainty evidence), and specificity was 97.5% (95% CI 93.6 to 99.0; 489 participants; high-certainty evidence). Xpert Ultra sensitivity was lower against a composite than a culture reference standard for all specimen types other than nasopharyngeal aspirate, while specificity was similar against both reference standards. Interpretation of results In theory, for a population of 1000 children: • where 100 have pulmonary tuberculosis in sputum (by culture): - 101 would be Xpert Ultra-positive, and of these, 26 (26%) would not have pulmonary tuberculosis (false positive); and - 899 would be Xpert Ultra-negative, and of these, 25 (3%) would have tuberculosis (false negative). • where 100 have pulmonary tuberculosis in gastric aspirate (by culture): - 123 would be Xpert Ultra-positive, and of these, 53 (43%) would not have pulmonary tuberculosis (false positive); and - 877 would be Xpert Ultra-negative, and of these, 30 (3%) would have tuberculosis (false negative). • where 100 have pulmonary tuberculosis in stool (by culture): - 74 would be Xpert Ultra-positive, and of these, 18 (24%) would not have pulmonary tuberculosis (false positive); and - 926 would be Xpert Ultra-negative, and of these, 44 (5%) would have tuberculosis (false negative). • where 100 have pulmonary tuberculosis in nasopharyngeal aspirate (by culture): - 66 would be Xpert Ultra-positive, and of these, 22 (33%) would not have pulmonary tuberculosis (false positive); and - 934 would be Xpert Ultra-negative, and of these, 56 (6%) would have tuberculosis (false negative). Detection of rifampicin resistance Xpert Ultra sensitivity was 100% (3 studies, 3 participants; very low-certainty evidence), and specificity range was 97% to 100% (3 studies, 128 participants; low-certainty evidence). Trace results Xpert Ultra trace results, regarded as positive in children by WHO standards, were common. Xpert Ultra specificity remained high in children, despite the frequency of trace results.

AUTHORS' CONCLUSIONS

We found Xpert Ultra sensitivity to vary by specimen type, with sputum having the highest sensitivity, followed by gastric aspirate and stool. Nasopharyngeal aspirate had the lowest sensitivity. Xpert Ultra specificity was high against both microbiological and composite reference standards. However, the evidence base is still limited, and findings may be imprecise and vary by study setting. Although we found Xpert Ultra accurate for detection of rifampicin resistance, results were based on a very small number of studies that included only three children with rifampicin resistance. Therefore, findings should be interpreted with caution. Our findings provide support for the use of Xpert Ultra as an initial rapid molecular diagnostic in children being evaluated for tuberculosis.

CRISPR detection of circulating cell-free Mycobacterium tuberculosis DNA in adults and children, including children with HIV: a molecular diagnostics study

BACKGROUND

Tuberculosis remains a leading cause of global mortality, especially for adults and children living with HIV (CLHIV) underdiagnosed by sputum-based assays. Non-sputum-based assays are needed to improve tuberculosis diagnosis and tuberculosis treatment monitoring. Our aim in this study was to determine whether ultrasensitive detection of Mycobacterium tuberculosis cell-free DNA (Mtb-cfDNA) in blood can diagnose tuberculosis and evaluate tuberculosis treatment responses.

METHODS

In this molecular diagnostics study we analysed archived serum from two patient populations evaluated for tuberculosis in Eswatini and Kenya to detect Mtb-cfDNA, analysing serum from all individuals who had both sufficient serum volumes and clear diagnostic results. An optimised CRISPR-mediated tuberculosis (CRISPR-TB) assay was used to detect Mtb-cfDNA in serum at enrolment from adults and children with presumptive tuberculosis and their asymptomatic household contacts, and at enrolment and during tuberculosis treatment from a cohort of symptomatic CLHIV at high risk for tuberculosis, who provided longitudinal serum at enrolment and during tuberculosis treatment.

FINDINGS

CRISPR-TB identified microbiologically and clinically confirmed tuberculosis cases in the predominantly HIV-negative Eswatini adult cohort with 96% sensitivity (27 [96%] of 28, 95% CI 80-100) and 94% specificity (16 [94%] of 17, 71-100), and with 83% sensitivity (5 [83%] of 6, 36-100) and 95% specificity (21 [95%] of 22, 77-100) in the paediatric cohort, including all six cases of extrapulmonary tuberculosis. In the Kenyan CLHIV cohort, CRISPR-TB detected all (13 [100%] of 13, 75-100) confirmed tuberculosis cases and 85% (39 [85%] of 46, 71-94) of unconfirmed tuberculosis cases diagnosed by non-microbiological clinical findings. CLHIV who were CRISPR-TB positive at enrolment had a 2·4-times higher risk of mortality by 6 months after enrolment. Mtb-cfDNA signal decreased after tuberculosis treatment initiation, with near or complete Mtb-cfDNA clearance by 6 months after tuberculosis treatment initiation.

INTERPRETATION

CRISPR-mediated detection of circulating Mtb-cfDNA shows promise to increase the identification of paediatric tuberculosis and HIV-associated tuberculosis, and potential for early diagnosis and rapid monitoring of tuberculosis treatment responses.

FUNDING

US Department of Defense, National Institute of Child Health and Human Development, National Institute of Allergy and Infectious Diseases, University of Washington Center for AIDS Research, and the Weatherhead Presidential Endowment fund.

Vikela Ekhaya: A Novel, Community-based, Tuberculosis Contact Management Program in a High Burden Setting

BACKGROUND

The prevention of tuberculosis (TB) in child contacts of TB cases and people living with human immunodeficiency virus (HIV) is a public health priority, but global access to TB preventive therapy (TPT) remains low. In 2019, we implemented Vikela Ekhaya, a novel community-based TB contact management program in Eswatini designed to reduce barriers to accessing TPT.

METHODS

Vikela Ekhaya offered differentiated TB and HIV testing for household contacts of TB cases by using mobile contact management teams to screen contacts, assess their TPT eligibility, and initiate and monitor TPT adherence in participants' homes.

RESULTS

In total, 945 contacts from 244 households were screened for TB symptoms; 72 (8%) contacts reported TB symptoms, and 5 contacts (0.5%) were diagnosed with prevalent TB. A total of 322 of 330 (98%) eligible asymptomatic household contacts initiated TPT. Of 322 contacts initiating TPT, 248 children initiated 3 months of isoniazid and rifampicin and 74 children and adults living with HIV initiated 6 months of isoniazid; 298 (93%) completed TPT. In clustered logistic regression analyses, unknown HIV status (adjusted odds ratio [aOR] 5.7, P = .023), positive HIV status (aOR 21.1, P = .001), urban setting (aOR 5.6, P = .006), and low income (aOR 5.9, P = .001) predicted loss from the cascade of care among TPT-eligible contacts.

CONCLUSION

Vikela Ekhaya demonstrated that community-based TB household contact management is a feasible, acceptable, and successful strategy for TB screening and TPT delivery. The results of this study support the development of novel, differentiated, community-based interventions for TB prevention and control.

Clinical standards for the diagnosis, treatment and prevention of TB infection

BACKGROUND: Tuberculosis (TB) preventive therapy (TPT) decreases the risk of developing TB disease and its associated morbidity and mortality. The aim of these clinical standards is to guide the assessment, management of TB infection (TBI) and implementation of TPT.METHODS: A panel of global experts in the field of TB care was identified; 41 participated in a Delphi process. A 5-point Likert scale was used to score the initial standards. After rounds of revision, the document was approved with 100% agreement.RESULTS: Eight clinical standards were defined: Standard 1, all individuals belonging to at-risk groups for TB should undergo testing for TBI; Standard 2, all individual candidates for TPT (including caregivers of children) should undergo a counselling/health education session; Standard 3, testing for TBI: timing and test of choice should be optimised; Standard 4, TB disease should be excluded prior to initiation of TPT; Standard 5, all candidates for TPT should undergo a set of baseline examinations; Standard 6, all individuals initiating TPT should receive one of the recommended regimens; Standard 7, all individuals who have started TPT should be monitored; Standard 8, a TBI screening and testing register should be kept to inform the cascade of care.CONCLUSION: This is the first consensus-based set of Clinical Standards for TBI. This document guides clinicians, programme managers and public health officers in planning and implementing adequate measures to assess and manage TBI.

HIV-Associated Tuberculosis in Children and Adolescents: Evolving Epidemiology, Screening, Prevention and Management Strategies

Children and adolescents living with HIV continue to be impacted disproportionately by tuberculosis as compared to peers without HIV. HIV can impact TB screening and diagnosis by altering screening and diagnostic test performance and can complicate prevention and treatment strategies due to drug-drug interactions. Post-tuberculosis lung disease is an underappreciated phenomenon in children and adolescents, but is more commonly observed in children and adolescents with HIV-associated tuberculosis. This review presents new data related to HIV-associated TB in children and adolescents. Data on the epidemiology of HIV-associated TB suggests that an elevated risk of TB in children and adolescents with HIV persists even with broad implementation of ART. Recent guidance also indicates the need for new screening strategies for HIV-associated TB. There have been major advances in the availability of new antiretroviral medications and also TB prevention options for children, but these advances have come with additional questions surrounding drug-drug interactions and dosing in younger age groups. Finally, we review new approaches to manage post-TB lung disease in children living with HIV. Collectively, we present data on the rapidly evolving field of HIV-associated child tuberculosis. This evolution offers new management opportunities for children and adolescents living with HIV while also generating new questions for additional research.

Transition to Dolutegravir Is Associated With an Increase in the Rate of Body Mass Index Change in a Cohort of Virally Suppressed Adolescents

Background

Antiretroviral therapy (ART) regimens that contain dolutegravir (DTG) have been associated with increases in body mass index (BMI) in adults. However, this relationship has not been well described in adolescents.

Methods

In a retrospective observational cohort of 460 virally suppressed (<200 copies/mL) adolescents living with human immunodeficiency virus at a clinical site in Eswatini, body mass index (BMI) measurements were analyzed between 1 year prior to the transition to DTG and up to 1 year after DTG transition. Random-effects linear spline models were used to describe the rate of change in BMI before and after the transition to DTG.

Results

In adolescents, BMI increased at a rate of 0.3 kg/m² per year before DTG transition and increased to a rate of 1.2 kg/m² per year after DTG transition. Sex of the adolescent modified the relationship between DTG and rate of BMI change: BMI rate of change after DTG transition was increased by 1.1 kg/m² in females and 0.6 kg/m² per year in males.

Conclusions

Transition to DTG in virally suppressed adolescents (aged 10–19 years) is associated with an increase in the rate of BMI change. Female adolescents may experience a larger change than males. Further investigation is required to elucidate the mechanism that underlies these observations and to assess how DTG impacts BMI in adolescents following longer durations of treatment.

The Magnitude of Interferon Gamma Release Assay Responses in Children With Household Tuberculosis Contact Is Associated With Tuberculosis Exposure and Disease Status

BACKGROUND

The clinical utility of the magnitude of interferon gamma (IFNγ) in response to mycobacterial antigens is unknown. We assessed the association between quantitative IFNγ response and degree of Mycobacterium tuberculosis exposure, infection and tuberculosis (TB) disease status in children.

METHODS

We completed cross-sectional analysis of children (≤15 years) exposed to an adult with bacteriologically confirmed TB, 2007-2012 in Cape Town, South Africa. IFNγ values were reported as concentrations and spot forming units for the QuantiFERON-TB Gold In-Tube (QFT-GIT) and T-SPOT.TB, respectively. Random-effects linear regression was used to investigate the relation between the M. tuberculosis contact score, clinical phenotype (TB diseased, infected, uninfected) and IFNγ▪response as outcome, adjusted for relevant covariates.

RESULTS

We analyzed data from 669 children (median age, 63 months; interquartile range, 33-108 months). A 1-unit increase in M. tuberculosis contact score was associated with an increase of IFNγ 0.60 international unit/mL (95% confidence interval [CI], 0.44-0.76 international unit/mL), and IFNγ spot forming unit 2 counts (95% CI, 1-3). IFNγ response was significantly lower among children with M. tuberculosis infection compared with children with TB disease (β = -1.42; 95% CI, -2.80 to -0.03) for the QFT-GIT, but not for the T-SPOT.TB. This association was strongest among children 2-5 years (β = -2.35 years; 95% CI, -4.28 to -0.42 years) and absent if <2 years.

CONCLUSIONS

The magnitude of IFNγ response correlated with the degree of recent M. tuberculosis exposure, measured by QFT-GIT and T-SPOT.TB, and was correlated with clinically relevant TB phenotypes using the QFT-GIT. IFNγ values are not only useful in estimating the risk of M. tuberculosis infection but may also support the diagnosis of TB disease in children.

DISCUSSION

The magnitude of IFNγ response correlated with the degree of recent M. tuberculosis exposure, measured by QFT-GIT and T-SPOT.TB, and was correlated with clinically relevant TB phenotypes using the QFT-GIT. IFNγ values are not only useful in estimating the risk of M. tuberculosis infection but may also support the diagnosis of TB disease in children.

Screening tests for active pulmonary tuberculosis in children

BACKGROUND

Globally, children under 15 years represent approximately 12% of new tuberculosis cases, but 16% of the estimated 1.4 million deaths. This higher share of mortality highlights the urgent need to develop strategies to improve case detection in this age group and identify children without tuberculosis disease who should be considered for tuberculosis preventive treatment. One such strategy is systematic screening for tuberculosis in high-risk groups.

OBJECTIVES

To estimate the sensitivity and specificity of the presence of one or more tuberculosis symptoms, or symptom combinations; chest radiography (CXR); Xpert MTB/RIF; Xpert Ultra; and combinations of these as screening tests for detecting active pulmonary childhood tuberculosis in the following groups. - Tuberculosis contacts, including household contacts, school contacts, and other close contacts of a person with infectious tuberculosis. - Children living with HIV. - Children with pneumonia. - Other risk groups (e.g. children with a history of previous tuberculosis, malnourished children). - Children in the general population in high tuberculosis burden settings.

SEARCH METHODS

We searched six databases, including the Cochrane Central Register of Controlled Trials, MEDLINE, and Embase, on 14 February 2020 without language restrictions and contacted researchers in the field.

SELECTION CRITERIA

Cross-sectional and cohort studies where at least 75% of children were aged under 15 years. Studies were eligible if conducted for screening rather than diagnosing tuberculosis. Reference standards were microbiological (MRS) and composite reference standard (CRS), which may incorporate symptoms and CXR.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed study quality using QUADAS-2. We consolidated symptom screens across included studies into groups that used similar combinations of symptoms as follows: one or more of cough, fever, or poor weight gain and one or more of cough, fever, or decreased playfulness. For combination of symptoms, a positive screen was the presence of one or more than one symptom. We used a bivariate model to estimate pooled sensitivity and specificity with 95% confidence intervals (CIs) and performed analyses separately by reference standard. We assessed certainty of evidence using GRADE.

MAIN RESULTS

Nineteen studies assessed the following screens: one symptom (15 studies, 10,097 participants); combinations of symptoms (12 studies, 29,889 participants); CXR (10 studies, 7146 participants); and Xpert MTB/RIF (2 studies, 787 participants). Several studies assessed more than one screening test. No studies assessed Xpert Ultra. For 16 studies (84%), risk of bias for the reference standard domain was unclear owing to concern about incorporation bias. Across other quality domains, risk of bias was generally low. Symptom screen (verified by CRS) One or more of cough, fever, or poor weight gain in tuberculosis contacts (4 studies, tuberculosis prevalence 2% to 13%): pooled sensitivity was 89% (95% CI 52% to 98%; 113 participants; low-certainty evidence) and pooled specificity was 69% (95% CI 51% to 83%; 2582 participants; low-certainty evidence). Of 1000 children where 50 have pulmonary tuberculosis, 339 would be screen-positive, of whom 294 (87%) would not have pulmonary tuberculosis (false positives); 661 would be screen-negative, of whom five (1%) would have pulmonary tuberculosis (false negatives). One or more of cough, fever, or decreased playfulness in children aged under five years, inpatient or outpatient (3 studies, tuberculosis prevalence 3% to 13%): sensitivity ranged from 64% to 76% (106 participants; moderate-certainty evidence) and specificity from 37% to 77% (2339 participants; low-certainty evidence). Of 1000 children where 50 have pulmonary tuberculosis, 251 to 636 would be screen-positive, of whom 219 to 598 (87% to 94%) would not have pulmonary tuberculosis; 364 to 749 would be screen-negative, of whom 12 to 18 (2% to 3%) would have pulmonary tuberculosis. One or more of cough, fever, poor weight gain, or tuberculosis close contact (World Health Organization four-symptom screen) in children living with HIV, outpatient (2 studies, tuberculosis prevalence 3% and 8%): pooled sensitivity was 61% (95% CI 58% to 64%; 1219 screens; moderate-certainty evidence) and pooled specificity was 94% (95% CI 86% to 98%; 201,916 screens; low-certainty evidence). Of 1000 symptom screens where 50 of the screens are on children with pulmonary tuberculosis, 88 would be screen-positive, of which 57 (65%) would be on children who do not have pulmonary tuberculosis; 912 would be screen-negative, of which 19 (2%) would be on children who have pulmonary tuberculosis. CXR (verified by CRS) CXR with any abnormality in tuberculosis contacts (8 studies, tuberculosis prevalence 2% to 25%): pooled sensitivity was 87% (95% CI 75% to 93%; 232 participants; low-certainty evidence) and pooled specificity was 99% (95% CI 68% to 100%; 3281 participants; low-certainty evidence). Of 1000 children, where 50 have pulmonary tuberculosis, 63 would be screen-positive, of whom 19 (30%) would not have pulmonary tuberculosis; 937 would be screen-negative, of whom 6 (1%) would have pulmonary tuberculosis. Xpert MTB/RIF (verified by MRS) Xpert MTB/RIF, inpatient or outpatient (2 studies, tuberculosis prevalence 1% and 4%): sensitivity was 43% and 100% (16 participants; very low-certainty evidence) and specificity was 99% and 100% (771 participants; moderate-certainty evidence). Of 1000 children, where 50 have pulmonary tuberculosis, 31 to 69 would be Xpert MTB/RIF-positive, of whom 9 to 19 (28% to 29%) would not have pulmonary tuberculosis; 969 to 931 would be Xpert MTB/RIF-negative, of whom 0 to 28 (0% to 3%) would have tuberculosis. Studies often assessed more symptoms than those included in the index test and symptom definitions varied. These differences complicated data aggregation and may have influenced accuracy estimates. Both symptoms and CXR formed part of the CRS (incorporation bias), which may have led to overestimation of sensitivity and specificity.

AUTHORS' CONCLUSIONS

We found that in children who are tuberculosis contacts or living with HIV, screening tests using symptoms or CXR may be useful, but our review is limited by design issues with the index test and incorporation bias in the reference standard. For Xpert MTB/RIF, we found insufficient evidence regarding screening accuracy. Prospective evaluations of screening tests for tuberculosis in children will help clarify their use. In the meantime, screening strategies need to be pragmatic to address the persistent gaps in prevention and case detection that exist in resource-limited settings.

Laboratory comparison of stool processing methods for Xpert® Ultra

TB disease diagnosis in children is difficult due to non-specific symptoms, paucibacillary disease and the need for invasive procedures to obtain diagnostic specimens. In many settings, these specimens are simply not collected and therefore stool, easily obtained, has emerged as a promising specimen for the diagnosis of child TB. In this study, stool from a healthy adult was spiked with known concentrations of bacille Calmette-Guérin vaccine and tested using the Xpert^® Ultra assay to determine the relative detection and error rate associated with four different published stool processing methods.

Tuberculosis among Children and Adolescents at HIV Treatment Centers in Sub-Saharan Africa

HIV-infected children and adolescents are at increased risk for tuberculosis (TB). Antiretroviral therapy (ART) reduces TB risk in HIV-infected adults, but its effectiveness in HIV-infected children and adolescents is unknown. We analyzed data from 7 integrated pediatric HIV/TB centers in 6 countries in sub-Saharan Africa. We used a Bayesian mixed-effect model to assess association between ART and TB prevalence and used adaptive lasso regression to analyze risk factors for adverse TB outcomes. The study period encompassed 57,525 patient-years and 1,160 TB cases (2,017 cases/100,000 patient-years). Every 10% increase in ART uptake resulted in a 2.33% reduction in TB prevalence. Favorable TB outcomes were associated with increased time in care and early ART initiation, whereas severe immunosuppression was associated with death. These findings support integrated HIV/TB services for HIV-infected children and adults and demonstrate the association of ART uptake with decreased TB incidence in high HIV/TB settings.

Evaluating antibiotic use and developing a tool to optimize prescribing in a family-centered HIV clinic in Eswatini

In a human immunodeficiency virus (HIV) clinic for children and their families in Eswatini, we sought to understand the use of antibiotics and identify specific areas for improvement. We performed a retrospective patient chart review as part of a quality improvement (QI) initiative to assess antimicrobial use before and after implementation of a standardized antimicrobial guide. For each prescribing period, 100 random patient encounters were selected for review if the indication for antibiotics, duration, and dose were consistent with World Health Organization (WHO) guidelines. Two physicians reviewed each encounter using a structured abstraction tool, with a third resolving discrepancies. Results were analyzed using a chi-square test of proportions and a structured survey was performed to assess perceptions of the guide. After the implementation of an antimicrobial guide, there was a significant decrease in the proportion of clinic visits with an antibiotic prescribed (p < 0.001). Incorrect indication for antimicrobial use decreased from 20.4% in the initial period to 10.31% and 10.2% but did not reach significance (p = .0621) in the subsequent periods after implementation. Incorrect dose/duration decreased from 10.47% in the initial period to 7.37% and 3.1% in the subsequent periods, but this was also was not significant (p = 0.139). All prescribers who completed the survey felt that it positively impacted their prescribing. Our study found that an antimicrobial guide reduced and improved the prescription of antimicrobials, demonstrating practical solutions can have a lasting impact on prescribing in low resource settings.

Distinct Risk Factors for Clinical and Bacteriologically Confirmed Tuberculosis among Child Household Contacts in a High-Burden Setting

The identification and screening of children at high risk of tuberculosis is essential to the control and prevention of child tuberculosis (TB). BUTIMBA, an active case finding and household contact-tracing project implemented between 2013 and 2015 in Eswatini, evaluated 5,413 contacts of 1,568 index cases, of whom 82 (1.5%) were diagnosed with TB disease. We conducted univariate and multivariate clustered logistic regression analyses of risk factors for any TB diagnosis among child household contacts of TB cases. Children younger than 5 years and children with positive HIV status were more likely to have TB than children aged 5-14 years and children with negative HIV status, respectively (adjusted odds ratio [aOR]: 2.2, P < 0.001; aOR: 5.0, P < 0.001). Children with one or more TB symptoms were more likely to be diagnosed with TB based on clinical criteria, but less likely to have bacteriologically confirmed TB, highlighting subjectivity in determination of child TB.

Xpert MTB/RIF and Xpert MTB/RIF Ultra assays for active tuberculosis and rifampicin resistance in children

BACKGROUND

Every year, at least one million children become ill with tuberculosis and around 200,000 children die. Xpert MTB/RIF and Xpert Ultra are World Health Organization (WHO)-recommended rapid molecular tests that simultaneously detect tuberculosis and rifampicin resistance in adults and children with signs and symptoms of tuberculosis, at lower health system levels. To inform updated WHO guidelines on molecular assays, we performed a systematic review on the diagnostic accuracy of these tests in children presumed to have active tuberculosis.

OBJECTIVES

Primary objectives • To determine the diagnostic accuracy of Xpert MTB/RIF and Xpert Ultra for (a) pulmonary tuberculosis in children presumed to have tuberculosis; (b) tuberculous meningitis in children presumed to have tuberculosis; (c) lymph node tuberculosis in children presumed to have tuberculosis; and (d) rifampicin resistance in children presumed to have tuberculosis - For tuberculosis detection, index tests were used as the initial test, replacing standard practice (i.e. smear microscopy or culture) - For detection of rifampicin resistance, index tests replaced culture-based drug susceptibility testing as the initial test Secondary objectives • To compare the accuracy of Xpert MTB/RIF and Xpert Ultra for each of the four target conditions • To investigate potential sources of heterogeneity in accuracy estimates - For tuberculosis detection, we considered age, disease severity, smear-test status, HIV status, clinical setting, specimen type, high tuberculosis burden, and high tuberculosis/HIV burden - For detection of rifampicin resistance, we considered multi-drug-resistant tuberculosis burden • To compare multiple Xpert MTB/RIF or Xpert Ultra results (repeated testing) with the initial Xpert MTB/RIF or Xpert Ultra result SEARCH METHODS: We searched the Cochrane Infectious Diseases Group Specialized Register, MEDLINE, Embase, Science Citation Index, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), Scopus, the WHO International Clinical Trials Registry Platform, ClinicalTrials.gov, and the International Standard Randomized Controlled Trials Number (ISRCTN) Registry up to 29 April 2019, without language restrictions.

SELECTION CRITERIA

Randomized trials, cross-sectional trials, and cohort studies evaluating Xpert MTB/RIF or Xpert Ultra in HIV-positive and HIV-negative children younger than 15 years. Reference standards comprised culture or a composite reference standard for tuberculosis and drug susceptibility testing or MTBDRplus (molecular assay for detection of Mycobacterium tuberculosis and drug resistance) for rifampicin resistance. We included studies evaluating sputum, gastric aspirate, stool, nasopharyngeal or bronchial lavage specimens (pulmonary tuberculosis), cerebrospinal fluid (tuberculous meningitis), fine needle aspirates, or surgical biopsy tissue (lymph node tuberculosis).

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed study quality using the Quality Assessment of Studies of Diagnostic Accuracy - Revised (QUADAS-2). For each target condition, we used the bivariate model to estimate pooled sensitivity and specificity with 95% confidence intervals (CIs). We stratified all analyses by type of reference standard. We assessed certainty of evidence using the GRADE approach.

MAIN RESULTS

For pulmonary tuberculosis, 299 data sets (68,544 participants) were available for analysis; for tuberculous meningitis, 10 data sets (423 participants) were available; for lymph node tuberculosis, 10 data sets (318 participants) were available; and for rifampicin resistance, 14 data sets (326 participants) were available. Thirty-nine studies (80%) took place in countries with high tuberculosis burden. Risk of bias was low except for the reference standard domain, for which risk of bias was unclear because many studies collected only one specimen for culture. Detection of pulmonary tuberculosis For sputum specimens, Xpert MTB/RIF pooled sensitivity (95% CI) and specificity (95% CI) verified by culture were 64.6% (55.3% to 72.9%) (23 studies, 493 participants; moderate-certainty evidence) and 99.0% (98.1% to 99.5%) (23 studies, 6119 participants; moderate-certainty evidence). For other specimen types (nasopharyngeal aspirate, 4 studies; gastric aspirate, 14 studies; stool, 11 studies), Xpert MTB/RIF pooled sensitivity ranged between 45.7% and 73.0%, and pooled specificity ranged between 98.1% and 99.6%. For sputum specimens, Xpert Ultra pooled sensitivity (95% CI) and specificity (95% CI) verified by culture were 72.8% (64.7% to 79.6%) (3 studies, 136 participants; low-certainty evidence) and 97.5% (95.8% to 98.5%) (3 studies, 551 participants; high-certainty evidence). For nasopharyngeal specimens, Xpert Ultra sensitivity (95% CI) and specificity (95% CI) were 45.7% (28.9% to 63.3%) and 97.5% (93.7% to 99.3%) (1 study, 195 participants). For all specimen types, Xpert MTB/RIF and Xpert Ultra sensitivity were lower against a composite reference standard than against culture. Detection of tuberculous meningitis For cerebrospinal fluid, Xpert MTB/RIF pooled sensitivity and specificity, verified by culture, were 54.0% (95% CI 27.8% to 78.2%) (6 studies, 28 participants; very low-certainty evidence) and 93.8% (95% CI 84.5% to 97.6%) (6 studies, 213 participants; low-certainty evidence). Detection of lymph node tuberculosis For lymph node aspirates or biopsies, Xpert MTB/RIF pooled sensitivity and specificity, verified by culture, were 90.4% (95% CI 55.7% to 98.6%) (6 studies, 68 participants; very low-certainty evidence) and 89.8% (95% CI 71.5% to 96.8%) (6 studies, 142 participants; low-certainty evidence). Detection of rifampicin resistance Xpert MTB/RIF pooled sensitivity and specificity were 90.0% (67.6% to 97.5%) (6 studies, 20 participants; low-certainty evidence) and 98.3% (87.7% to 99.8%) (6 studies, 203 participants; moderate-certainty evidence).

AUTHORS' CONCLUSIONS

We found Xpert MTB/RIF sensitivity to vary by specimen type, with gastric aspirate specimens having the highest sensitivity followed by sputum and stool, and nasopharyngeal specimens the lowest; specificity in all specimens was > 98%. Compared with Xpert MTB/RIF, Xpert Ultra sensitivity in sputum was higher and specificity slightly lower. Xpert MTB/RIF was accurate for detection of rifampicin resistance. Xpert MTB/RIF was sensitive for diagnosing lymph node tuberculosis. For children with presumed tuberculous meningitis, treatment decisions should be based on the entirety of clinical information and treatment should not be withheld based solely on an Xpert MTB/RIF result. The small numbers of studies and participants, particularly for Xpert Ultra, limits our confidence in the precision of these estimates.

Point-of-Care Testing to Guide Treatment and Estimate Risk Factors for Sexually Transmitted Infections in Adolescents and Young People With Human Immunodeficiency Virus in Eswatini

Background

The World Health Organization (WHO) estimates 127 million new cases of Chlamydia trachomatis (CT), 87 million new cases of Neisseria gonorrhea (NG), and 156 million new cases of Trichomonas vaginalis (TV) each year, which corresponds to 355 (219-606), 303 (216-468), and 243 (97.6-425) thousand disability-adjusted life-years. In low-resource settings, however, sexually transmitted infections (STIs) are treated syndromically and many individuals with asymptomatic infection may be missed, especially adolescents and young adults with human immunodeficiency virus (HIV).

Methods

We enrolled patients aged 15-24 with HIV (N = 300) attending a family-centered HIV clinic in Mbabane, Eswatini. Participants completed a sexual history questionnaire and provided urine as well as oropharyngeal and/or vaginal swabs, if sexually active, for testing with Xpert CT/NG and TV tests. Analysis included bivariate and multivariate odds ratios and test sensitivity and specificity.

Results

Sexually transmitted infection rates were highest (25.0%; 95% confidence interval [CI], 15.2-37.3) in females ages 20-24 who were ever sexually active. In patients with confirmed STIs, NG (15 of 32, 47%) was more common than CT (9 of 32, 28%) and TV (8 of 32, 25%). Syndromic screening alone had a sensitivity of 32.0% (95% CI, 14.9-53.3) and specificity of 86.0% (95% CI, 79.0-91.4) but varied by gender. The presence of an STI was associated with reporting new sexual partner(s) (OR = 2.6; 95% CI, 1.1-6.4), sometimes to never using condoms (OR = 4.2; 95% CI, 1.7-10.2), most recent sexual partner >25 years old (OR = 3.2; 95% CI, 1.3-7.9), and HIV diagnosis at age ≥15 years (OR = 3.4; 95% CI, 1.4-8.2).

Conclusions

Syndromic screening alone performed poorly. Routine diagnostic testing significantly increases STI detection and should be considered in high-risk populations, such as adolescents and young adults with HIV.

Evaluation of the QuantiFERON-Tuberculosis Gold Plus Assay in Children with Tuberculosis Disease or Following Household Exposure to Tuberculosis

Interferon-gamma release assays are increasingly used in children to establish evidence of tuberculosis (TB) infection and to assist in the diagnosis of TB disease. The QuantiFERON-TB Gold In-Tube assay is being phased out in favor of a next-generation test, the QuantiFERON-TB Gold Plus (QFT-Plus) assay. The QFT-Plus assay is designed with two antigen tubes to differentially stimulate CD4⁺ and CD8⁺ T cells. The performance of this assay has been documented extensively in adults but has not yet been evaluated in children. Here, we compare the performance of the two assays in a cohort of 46 children exposed to TB and 12 children diagnosed with TB disease in Eswatini. The tests demonstrated excellent concordance in both TB disease (100% agreement, Cohen's kappa = 1) and TB infection (96% agreement, Cohen's kappa = 0.91). Most of the children with household exposure tested negative for TB infection by both tests, indicating the ongoing need for new tests for TB infection that can be easily implemented in TB high-burden settings at minimal cost.

Pregnancy-Induced Alterations in NK Cell Phenotype and Function

Pregnant women are particularly susceptible to complications of influenza A virus infection, which may result from pregnancy-induced changes in the function of immune cells, including natural killer (NK) cells. To better understand NK cell function during pregnancy, we assessed the ability of the two main subsets of NK cells, CD56^dim, and CD56^bright NK cells, to respond to influenza-virus infected cells and tumor cells. During pregnancy, CD56^dim and CD56^bright NK cells displayed enhanced functional responses to both infected and tumor cells, with increased expression of degranulation markers and elevated frequency of NK cells producing IFN-γ. To better understand the mechanisms driving this enhanced function, we profiled CD56^dim and CD56^bright NK cells from pregnant and non-pregnant women using mass cytometry. NK cells from pregnant women displayed significantly increased expression of several functional and activation markers such as CD38 on both subsets and NKp46 on CD56^dim NK cells. NK cells also displayed diminished expression of the chemokine receptor CXCR3 during pregnancy. Overall, these data demonstrate that functional and phenotypic shifts occur in NK cells during pregnancy that can influence the magnitude of the immune response to both infections and tumors.

Interferon-γ Release Assay Performance for Tuberculosis in Childhood

BACKGROUND

Interferon-γ release assays (IGRAs) are important adjunctive tests for diagnosing tuberculosis (TB) disease in children.

METHODS

We analyzed California TB registry data for patients ≤18 years with laboratory-confirmed TB disease during 2010-2015 to identify case characteristics associated with test selection and performance and measure IGRA sensitivity.

RESULTS

In total, 778 cases of TB were reported; 360 were laboratory confirmed. Indeterminate IGRAs were associated with being <1 year old (prevalence rate ratio 9.23; 95% confidence interval 2.87 to 29.8) and having central nervous system disease (prevalence rate ratio 2.69; 95% confidence interval 1.06 to 6.86) on multivariable analysis. Ninety-five children had both an IGRA and tuberculin skin test (TST) performed. Among those, the sensitivity of IGRA in 5- to 18-year-olds was 96% (66 out of 69) vs 83% (57 out of 69) for TST (P = .01); IGRA sensitivity compared with TST in children ages 2 to 4 was 91% (10 out of 11) vs 91% (10 out of 11) (P > .99), and the sensitivity compared with TST in children aged <2 years was 80% (12 out of 15) vs 87% (13 out of 15) (P > .99).

CONCLUSIONS

This is the largest North American analysis of IGRA use and performance among children with TB disease. In children <5 years old, IGRA sensitivity is similar to TST, but sensitivity of both tests are reduced in children <2 years old. Indeterminate results are higher in children <1 year old and in central nervous system disease. In children ≥5 years old with laboratory-confirmed TB, IGRA has greater sensitivity than TST and should be considered the preferred immunodiagnostic test..

Diagnostic and Treatment Monitoring Potential of A Stool-Based Quantitative Polymerase Chain Reaction Assay for Pulmonary Tuberculosis

A quantifiable, stool-based, Mycobacterium tuberculosis (Mtb) test has potential complementary value to respiratory specimens. Limit of detection (LOD) was determined by spiking control stool. Clinical test performance was evaluated in a cohort with pulmonary tuberculosis (TB) (N = 166) and asymptomatic household TB child contacts (N = 105). Stool-quantitative polymerase chain reaction (qPCR) results were compared with sputum acid-fast bacilli (AFB) microscopy, GeneXpert MTB/RIF (Xpert MTB/RIF), and cultures. In Mtb stool-spiking studies, the LOD was 96 colony-forming units/50 mg of stool (95% confidence interval [CI]: 84.8-105.6). Among specimens collected within 72 hours of antituberculosis treatment (ATT) initiation, stool qPCR detected 22 of 23 (95%) of culture-positive cases. Among clinically diagnosed cases that were Xpert MTB/RIF and culture negative, stool qPCR detected an additional 8% (3/37). Among asymptomatic, recently TB-exposed participants, stool PCR detected Mtb in two of 105 (1.9%) patients. Two months after ATT, the Mtb quantitative burden in femtogram per microliters decreased (Wilcoxon signed-rank P < 0.001) and persistent positive stool PCR was associated with treatment failure or drug resistance (relative risk 2.8, CI: 1.2-6.5; P = 0.012). Stool-based qPCR is a promising complementary technique to sputum-based diagnosis. It detects and quantifies low levels of stool Mtb DNA, thereby supporting adjunct diagnosis and treatment monitoring in pulmonary TB.

Leveraging tuberculosis case relative locations to enhance case detection and linkage to care in Swaziland

BACKGROUND

In Swaziland, as in many high HIV/TB burden settings, there is not information available regarding the household location of TB cases for identifying areas of increased TB incidence, limiting the development of targeted interventions. Data from "Butimba", a TB REACH active case finding project, was re-analyzed to provide insight into the location of TB cases surrounding Mbabane, Swaziland.

OBJECTIVE

The project aimed to identify geographical areas with high TB burdens to inform active case finding efforts.

METHODS

Butimba implemented household contact tracing; obtaining landmark based, informal directions, to index case homes, defined here as relative locations. The relative locations were matched to census enumeration areas (known location reference areas) using the Microsoft Excel Fuzzy Lookup function. Of 403 relative locations, an enumeration area reference was detected in 388 (96%). TB cases in each census enumeration area and the active case finders in each Tinkhundla, a local governmental region, were mapped using the geographic information system, QGIS 2.16.

RESULTS

Urban Tinkhundla predictably accounted for most cases; however, after adjusting for population, the highest density of cases was found in rural Tinkhundla. There was no correlation between the number of active case finders currently assigned to the 7 Tinkhundla surrounding Mbabane and the total number of TB cases (Spearman rho = -0.57, p = 0.17) or the population adjusted TB cases (Spearman rho = 0.14, p = 0.75) per Tinkhundla.

DISCUSSION

Reducing TB incidence in high-burden settings demands novel analytic approaches to study TB case locations. We demonstrated the feasibility of linking relative locations to more precise geographical areas, enabling data-driven guidance for National Tuberculosis Programs' resource allocation. In collaboration with the Swazi National Tuberculosis Control Program, this analysis highlighted opportunities to better align the active case finding national strategy with the TB disease burden.

Increased Proinflammatory Responses of Monocytes and Plasmacytoid Dendritic Cells to Influenza A Virus Infection During Pregnancy

Pregnancy-induced alterations in immunity may contribute to the increased morbidity associated with influenza A virus infection during pregnancy. We characterized the immune response of monocytes and plasmacytoid dendritic cells (pDCs) to influenza A virus infection in 21 pregnant and 21 nonpregnant women. In pregnant women, monocytes and pDCs exhibit an exaggerated proinflammatory immune response to 2 strains of influenza A virus, compared with nonpregnant women, characterized by increased expression of major histocompatibility complex class II (approximately 2.0-fold), CD69 (approximately 2.2-fold), interferon γ-induced protein 10 (approximately 2.0-fold), and macrophage inflammatory protein 1β (approximately 1.5-fold). This enhanced innate inflammatory response during pregnancy could contribute to pulmonary inflammation following influenza A virus infection.

Application of Mass Cytometry (CyTOF) for Functional and Phenotypic Analysis of Natural Killer Cells

Mass cytometry is a novel platform for high-dimensional phenotypic and functional analysis of single cells. This system uses elemental metal isotopes conjugated to monoclonal antibodies to evaluate up to 42 parameters simultaneously on individual cells with minimal overlap between channels. The platform can be customized for analysis of both phenotypic and functional markers. Here, we will describe methods to stain, collect, and analyze intracellular functional markers and surface phenotypic markers on natural killer cells.

Pregnancy Does Not Attenuate the Antibody or Plasmablast Response to Inactivated Influenza Vaccine

BACKGROUND

Inactivated influenza vaccine (IIV) is recommended during pregnancy to prevent influenza infection and its complications in pregnant women and their infants. However, the extent to which pregnancy modifies the antibody response to vaccination remains unclear, and prior studies have focused primarily on hemagglutinin inhibition (HI) titers. A more comprehensive understanding of how pregnancy modifies the humoral immune response to influenza vaccination will aid in maximizing vaccine efficacy.

METHODS

Healthy pregnant women and control women were studied prior to, 7 days after, and 28 days after vaccination with IIV. HI titers, microneutralization (MN) titers, and the frequency of circulating plasmablasts were evaluated in pregnant versus control women.

RESULTS

Pregnant women and control women mount similarly robust serologic immune responses to IIV, with no significant differences for any influenza strain in postvaccination geometric mean HI or MN titers. HI and MN titers correlate, though MN titers demonstrate more robust changes pre- versus postvaccination. The induction of circulating plasmablasts is increased in pregnant women versus controls (median fold-change 2.60 vs 1.49 [interquartile range, 0.94-7.53 vs 0.63-2.67]; P = .03).

CONCLUSIONS

Pregnant women do not have impaired humoral immune responses to IIV and may have increased circulating plasmablast production compared to control women.

Immunogenicity and Clinical Efficacy of Influenza Vaccination in Pregnancy

Pregnant women are at high risk from influenza due to disproportionate morbidity, mortality, and adverse pregnancy outcomes following infection. As such, they are classified as a high-priority group for vaccination. However, changes in the maternal immune system required to accommodate the allogeneic fetus may alter the immunogenicity of influenza vaccines. A large number of studies have evaluated the safety of the influenza vaccine. Here, we will review available studies on the immunogenicity and efficacy of the influenza vaccine during pregnancy, focusing on both humoral and cellular immunity.

Time of onset of carcinoma of the stomach following surgical treatment of duodenal ulcer

In a review of 1,092 patients with histologically proved carcinoma of the stomach, it was found that 40 patients (3.8 per cent) had previously undergone surgical treatment of a duodenal ulcer. In 13 patients, truncal vagotomy had been carried out, while 27 patients had a partial gastrectomy. Patients having truncal vagotomy and who subsequently had carcinoma of the stomach develop did so at a significantly earlier age than those having partial gastrectomy (55 years compared with 64 years). Carcinoma of the stomach was diagnosed after an average interval of 8.5 years in the vagotomy group compared with 24.0 years in the nonvagotomy group. Possible explanations for this observation are considered. Patients in the vagotomy group were less likely to have a resectable tumor.

Results of adrenal surgery in patients with hypertension, aldosterone excess, and low plasma renin concentration

Fifty patients with hypertension, aldosterone excess, and low plasma renin concentration underwent adrenal surgery. There was a highly significant fall in mean systolic and diastolic pressures after the operation. The mean postoperative diastolic pressure fell to strictly normal levels, however, in only 19 out of 38 patients from whom an adrenocortical adenoma was removed and in only two out of 10 non-tumour patients. There was a significant correlation between the fall in blood pressure during spironolactone treatment and after adrenal surgery though levels were generally slightly lower during the former therapy. It is suggested that removal of an aldosterone-producing adenoma is the treatment of choice provided a good preoperative hypotensive response to spironolactone occurs, while the treatment of choice for non-tumour patients is often long-term spironolactone.

Truncal vagotomy and drainage for chronic duodenal ulcer disease: a controlled trial

The results of elective truncal vagotomy and drainage in 547 duodenal ulcer patients are reported. Altogether, 204 patients were randomly allocated to pyloroplasty and 200 to gastrojejunostomy. In 101 patients gastrojejunostomy was electively chosen and in 42 patients the duodenum was opened to confirm the diagnosis. Operative mortality was 0.5%, the incidence of proved recurrent ulceration 3.3%, severe dumping 2%, and severe diarrhoea 1.1%. There were no significant differences between the groups, with the exception of bilious vomiting which occurred more often in patients with gastrojejunostomy.

Exocrine secretory responses of the pancreas to insulin and to a meat meal in dogs

Studies in five dogs with chronic pancreatic and gastric fistulae have shown that insulin-induced vagal stimulation of the pancreas (gastric fistula open) resulted in protein and bicarbonate outputs very much smaller than those obtained with a 400-g meat meal. However, when the insulin-activated gastric acid secretion was allowed access to the duodenum (gastric fistula closed) peak outputs of both bicarbonate and protein were observed which were closely similar to the response to the meal. These findings suggest that insulin-induced hypoglycaemia results in stimulation of the pancreas within the physiological range when gastric acid is allowed access to the duodenum with consequent release of secretin.

A study of the acid dose-response curve to small doses of pentagastrin in duodenal ulcer patients

1. The acid secretory responses to a range of small doses of pentagastrin in 0·15 m-NaCl have been studied in thirty-one preoperative duodenal ulcer subjects. Acid output increased significantly above basal values when a dose of 0·064 μg h−1 kg−1 was given.

2. Control observations in sixteen duodenal ulcer patients using the saline solvent alone at identical rates of infusion showed no significant increase in acid output.

3. From the dose-response curves sub-threshold and threshold doses of pentapeptide are suggested for duodenal ulcer patients before truncal vagotomy.

4. Considerable variation in acid response was noted between patients given the same body-weight dose of pentapeptide. The results suggest that a ‘twilight zone’ of stimulation exists between the dose of pentagastrin by which few patients are stimulated and the dose by which the majority are stimulated. This may reflect some variation in the sensitivity to stimulation by pentagastrin from one patient to another.

The effect of sub-threshold doses of pentagastrin on the acid response to insulin in duodenal ulcer subjects before and after truncal vagotomy

1. On the basis of previously described dose-response curves, small doses of pentagastrin were infused in duodenal ulcer patients before and after vagotomy. No increase or decrease in gastric acid output was noted, confirming that the doses of pentagastrin used were sub-threshold.

2. In twenty-six duodenal ulcer patients the effect of sub-threshold doses of pentagastrin on the insulin response resulted in three distinct patterns. (i) In subjects with clearly functioning vagal pathways, no increase in acid output occurred after insulin when a sub-threshold dose of pentagastrin was added; (ii) patients with equivocal acid responses to insulin alone showed augmentation of acid output when given insulin and a sub-threshold pentagastrin infusion; (iii) patients with no response to insulin after truncal vagotomy showed some increase in acid output to the combined agents, and in two patients, criteria for a clearly positive acid response were satisfied.

3. We conclude from these studies that potentiation exists between insulin-induced cholinergic stimulation and infusion of sub-threshold doses of pentagastrin in man.

The effect of vagotomy on the lower part of the acid dose-response curve to pentagastrin in man

1. The acid secretory responses to insulin of forty-seven duodenal ulcer patients after truncal vagotomy and drainage were classified according to the criteria of Hollander (1946) into positive or negative.

2. The acid response to ranges of small doses of pentagastrin was studied in these two groups. In the group with a positive acid response after insulin the dose-response pattern to pentagastrin was very similar to that in preoperative patients.

3. In those who failed to satisfy criteria for a positive response after insulin the dose-response curve to pentagastrin appeared to shift to the right. It had a lower level and a smaller slope. Truncal vagotomy appeared to cause an eightfold increase in the threshold dose found in preoperative patients.

4. Supersensitivity of the stomach to small doses of pentagastrin after vagotomy was not apparent in the present study.