Feasibility and utility of a combined nasogastric-tube-and-string-test device for bacteriologic confirmation of pulmonary tuberculosis in young children

Abstract

For microbiological confirmation of pediatric pulmonary tuberculosis (PTB), gastric aspirates (GA) are often operationally unfeasible without hospitalization, and the encapsulated orogastric string test is not easily swallowed in young children. The Combined-NasoGastric-Tube-and-String-Test (CNGTST) enables dual collection of GA and string specimens. In a prospective cohort study in Kenya, we examined its feasibility in children under five with presumptive PTB and compared the bacteriological yield of string to GA. Paired GA and string samples were successfully collected in 95.6 % (281/294) of children. Mycobacterium tuberculosis was isolated from 7.0 % (38/541) of GA and 4.3 % (23/541) of string samples, diagnosing 8.2 % (23/281) of children using GA and 5.3 % (15/281) using string. The CNGTST was feasible in nearly all children. Yield from string was two-thirds that of GA despite a half-hour median dwelling time. In settings where the feasibility of hospitalisation for GA is uncertain, the string component can be used to confirm PTB.

Keywords: Diagnosis; Gastric aspirate; Microbiological confirmation; Pediatric tuberculosis; String.

Figure 1:. Photo of the Combined Nasogastric Tube and String test (CNGTST)

This device is made up a nylon thread wrapped around the outside of a nasogastric tube used for gastric aspiration.

Figure 2:. Flow diagram of gastric aspirate and string test sample collection.

GA: gastric aspirate; ST: string test; Xpert: Xpert MTB/RIF; MGIT: mycobacteria growth indicator tube *Interpretable results are those with positive or negative Xpert or MGIT results. Uninterpretable results include contaminated or indeterminate samples.

Figure 3:. Unadjusted and adjusted odds ratios of factors associated with a positive M. tuberculosis finding on string test samples, by per-specimen analysis (n = 1082) and per-patient analysis (n = 296).

Immunological status for HIV infected children defined using World Health Organization criteria [18]. Ref: Reference; CXR: chest X ray; TB; tuberculosis; CI: confidence intervals.

Figure 4:. Unadjusted odds ratios of M. tuberculosis positive string test result among samples with an M. tuberculosis positive gastric aspirate (n = 38).

Models for HIV and Immunological evidence of TB infection did not converge. Ref: Reference; CXR: chest X ray; TB; tuberculosis; CI: confidence intervals.