Sensitive and Feasible Specimen Collection and Testing Strategies for Diagnosing Tuberculosis in Young Children

Abstract

Importance: Criterion-standard specimens for tuberculosis diagnosis in young children, gastric aspirate (GA) and induced sputum, are invasive and rarely collected in resource-limited settings. A far less invasive approach to tuberculosis diagnostic testing in children younger than 5 years as sensitive as current reference standards is important to identify.

Objective: To characterize the sensitivity of preferably minimally invasive specimen and assay combinations relative to maximum observed yield from all specimens and assays combined.

Design, setting, and participants: In this prospective cross-sectional diagnostic study, the reference standard was a panel of up to 2 samples of each of 6 specimen types tested for Mycobacterium tuberculosis complex by Xpert MTB/RIF assay and mycobacteria growth indicator tube culture. Multiple different combinations of specimens and tests were evaluated as index tests. A consecutive series of children was recruited from inpatient and outpatient settings in Kisumu County, Kenya, between October 2013 and August 2015. Participants were children younger than 5 years who had symptoms of tuberculosis (unexplained cough, fever, malnutrition) and parenchymal abnormality on chest radiography or who had cervical lymphadenopathy. Children with 1 or more evaluable specimen for 4 or more primary study specimen types were included in the analysis. Data were analyzed from February 2015 to October 2020.

Main outcomes and measures: Cumulative and incremental diagnostic yield of combinations of specimen types and tests relative to the maximum observed yield.

Results: Of the 300 enrolled children, the median (interquartile range) age was 2.0 (1.0-3.6) years, and 151 (50.3%) were female. A total of 294 met criteria for analysis. Of 31 participants with confirmed tuberculosis (maximum observed yield), 24 (sensitivity, 77%; interdecile range, 68%-87%) had positive results on up to 2 GA samples and 20 (sensitivity, 64%; interdecile range, 53%-76%) had positive test results on up to 2 induced sputum samples. The yields of 2 nasopharyngeal aspirate (NPA) samples (23 of 31 [sensitivity, 74%; interdecile range, 64%-84%]), of 1 NPA sample and 1 stool sample (22 of 31 [sensitivity, 71%; interdecile range, 60%-81%]), or of 1 NPA sample and 1 urine sample (21.5 of 31 [sensitivity, 69%; interdecile range, 58%-80%]) were similar to reference-standard specimens. Combining up to 2 each of GA and NPA samples had an average yield of 90% (28 of 31).

Conclusions and relevance: NPA, in duplicate or in combination with stool or urine specimens, was readily obtainable and had diagnostic yield comparable with reference-standard specimens. This combination could improve tuberculosis diagnosis among children in resource-limited settings. Combining GA and NPA had greater yield than that of the current reference standards and may be useful in certain clinical and research settings.

Figure 1.. Participant-Level Mycobacterial Results for 32 Children Tested for Tuberculosis Between October 2013 and August 2015 in Kisumu County, Kenya

Dot plot of participant-level results for fluorescence microscopy, Xpert MTB/RIF (Cepheid), and mycobacteria growth indicator tube (MGIT) by sample type and sample number. Up to 2 samples of each type were tested per participant. Black circles indicate a positive result, gray circles indicate an invalid (Xpert MTB/RIF) or contaminated (MGIT) result, and white circles indicate a negative result. The top 7 rows are results for participants with HIV. The column on the right shows the number of positive results by Xpert MTB/RIF or MGIT over the number of evaluable specimens. Participants are sorted vertically in descending order of number of testing results available. FNA indicates fine-needle aspiration; GA, gastric aspirate; IS, induced sputum; NPA, nasopharyngeal aspirate; ST, string test.

Figure 2.. Cumulative and Incremental Diagnostic Yield by Specimen Type Among 31 Children With Tuberculosis

The cumulative and incremental yield of each specimen type among 31 analyzable participants is depicted as 3 groups of 3 bars: yield of 1 specimen, yield of 2 specimens, and the incremental yield of the second specimen when added to the first; specimens were tested by Xpert MTB/RIF (Cepheid) alone, mycobacteria growth indicator tube (MGIT) alone, and both Xpert MTB/RIF and MGIT. The points depict average yield over the resampling distribution, black bars represent the interquartile range, and gray bars represent the interdecile range (10th to 90th centile). The specimen types are arranged in decreasing order of yield.

Figure 3.. Average Cumulative Yield of Confirmed Cases by Number of Specimen Samples Among 31 Children With Confirmed Tuberculosis

The average yield for 31 analyzable participants over all combinations of specimens is depicted in groups of 3 for all combinations of each number of specimens from 1 to 12: yield for Xpert MTB/RIF (Cepheid) alone, yield for mycobacteria growth indicator tube (MGIT) alone, and yield for both Xpert MTB/RIF and MGIT. The points depict average yield over the resampling distribution, black bars represent the interquartile range, and gray bars represent the interdecile range (10th to 90th centile).

Figure 4.. Incremental Sequence of High-Yield Combinations and Highest-Diagnostic-Yield Combinations for Testing Minimally Invasive Specimen Types From Children for Tuberculosis

Boxes show the average diagnostic yield on resampling participants bacteriologic test results (Xpert MTB/RIF [Cepheid] or mycobacteria growth indicator tube [MGIT]), with corresponding specimens and number of each specimen. The boxes on the left show results for single specimens with the highest yield. Connecting lines between boxes indicate which specimen type is added for the next box in the series. At each step, the specimen or specimens that contribute the greatest number of additional positive bacteriologic results is shown.