Original Research

Tuberculosis in the Torres Strait: the lady doth test too much

AUTHORS

J'Belle Foster1 Master of Public Health / PhD Scholar, Nursing Director Torres and Cape Tuberculosis Control Unit / PhD Scholar *

Ben Marais2 FRACP, PhD, Professor Paediatrics & Child Health / Co-director Marie Bashir Institute for Infectious Diseases and Biosecurity

Rotona L Martin3 Indigenous Health Worker, Torres and Cape Tuberculosis Control Unit

Dunstan Peniyamina4 Cross Border Communication Officer

Diana Mendez5 Doctoral Studies Mentor

Jeffrey Warner6 Associate Professor

Emma McBryde7 Professorial Research Fellow – Infectious Disease and Epidemiology / TB Specialist Torres and Cape Tuberculosis Control Unit

AFFILIATIONS

1 College of Medicine and Dentistry, James Cook University, 1 James Cook Drive, Townsville, Qld 4811, Australia

2 The Children's Hospital at Westmead, Sydney, NSW 2145, Australia

3 Saibai Primary Health Centre, Saibai Island, Qld 4875, Australia

4 Cairns Tropical Public Health Unit, William McCormack Place II, Level 7, 5 Sheridan St, Cairns, Qld 4870, Australia

5, 7 Australian Institute of Tropical Health & Medicine, James Cook University, 1 James Cook Drive, Townsville, Qld 4811, Australia

6 College of Public Health, Medical & Vet Sciences, James Cook University, 1 James Cook Drive, Townsville, Qld 4811, Australia

ACCEPTED: 3 December 2020


early abstract:

Introduction: Smear-positive pulmonary tuberculosis (PTB) requires rapid diagnosis and treatment to prevent ongoing transmission. Collection of two sputum specimens is considered the minimum requirement for the diagnosis of PTB but current guidelines in the Torres Strait Islands, Australia, recommend three sputum specimens; this frequently delays treatment initiation.
Methods: A retrospective study was performed to ascertain the diagnostic yield of sputum specimens collected in the Torres Strait Islands. The study assessed demographics and characteristics of all PTB cases diagnosed between 2000 and 2018, and assessed the diagnostic yield in 143 cases in whom at least three sputum specimens had been collected prior to treatment commencement. Incremental and cumulative yield was calculated for each sputum specimen. Data were further analysed using binary logistic regression to examine the association between selected characteristics and a smear-positive acid-fast bacilli (AFB) result. 
Results: Overall, AFB was detected from the first or second sputum specimen in 97 of 101 PTB cases that were sputum smear positive. A smear positive result was more common (OR 2.84, 95% CI 1.08, 7.46) for Papua New Guinea Nationals compared to Australian born patients. Of the 429 samples collected, 76 (18%) were of poor quality and the association between poor quality specimens and smear negative results was significant (p <0.01). Among sputum smear-negative cases, 5/42 (12%) had three consecutive poor quality specimens. The most common collection modality in adults was voluntary expectoration; done in 391/429 (91%) of all specimens collected. Alternative specimen collection methods were mainly used in children; induced sputum 1/429 (.2%), gastric aspirate 26/429 (6%) and nasopharyngeal aspirate 7/429 (1.6%). Errors with labelling, packaging and transportation occurred in 44 specimens from 15 patients.
Conclusion: Two good quality specimens ensure adequate diagnostic yield for PTB and a third specimen should only be collected from patients with two negative specimens who have persistent symptoms. Ideally, decentralised Xpert Ultra® should be the frontline diagnostic test in remote settings, especially in a setting like the Torres Strait Islands with high rates of drug resistant TB.