New recommendations for duration of respiratory isolation based on time to detect Mycobacterium tuberculosis in liquid culture

Abstract

It was hypothesised that the time to detect Mycobacterium tuberculosis in liquid culture of sputum from patients with pulmonary tuberculosis may be a better indicator for the duration of respiratory isolation than sputum smear status.Pre-treatment and during-treatment sputum acid-fast bacilli (AFB) smear and culture results were reviewed in 284 patients with pulmonary tuberculosis. The time to detect M. tuberculosis in liquid culture (TTD-TB) was the number of days from inoculation of the Mycobacterial Growth Indicator Tube to culture detection and visualisation of AFB.The median (interquartile range) TTD-TB for smear group 0 (no bacilli seen) was 14 (12-20) days. This value was used as the standard at which release from isolation could be permitted. In smear group 4 (.9 AFB per high-power field (hpf) in sputum specimens before treatment) patients, the TTD-TB exceeded 14 days after a median of 25 days of treatment.The current authors recommend that patients in smear groups 1 and 2 (1-9 AFB per 100 hpf and 1-9 AFB per 10 hpf in sputum specimens before treatment, respectively) receive treatment in respiratory isolation for 7 days, provided the risk of drug resistance is low. Smear group 3 (1-9 AFB per hpf) and 4 patients should receive treatment in respiratory isolation for 14 and 25 days, respectively. These criteria would have reduced the duration of respiratory isolation by 1,516 days in the 143 study participants with sputum smear-positive pulmonary tuberculosis.Provided clinical and radiographical criteria are satisfactory, use of the time to detect Mycobacterium tuberculosis in liquid culture could enable the duration of respiratory isolation to be predicted from the pre-treatment sputum smear grade. The recommendations enable isolation to end well before sputum becomes smear negative, with considerable benefits to patients and healthcare providers.

Culture Conversion Rate at 2 Months of Treatment According to Diagnostic Methods among Patients with Culture-Positive Pulmonary Tuberculosis

“…Having a high bacillary burden implies stronger infectivity and requires a longer isolation period and more intensive treatment [16]. Based on our finding that pulmonary TB patients who had negative results on a smear or those who were diagnosed using bronchoscopic specimens showed a shorter time to negative conversion than those with smear-positive pulmonary TB, the duration of isolation could be shorter than the conventionally recommended 2 weeks for TB patients [17].…”

Comparison of Quantitative Techniques including Xpert MTB/RIF to Evaluate Mycobacterial Burden

“…Already incorporated into EBA studies [12], [13] TTP has been well correlated with bacterial load [7], [13], [14]. Its user-friendly format, automation, high discriminative ability and low detection threshold (less than 10 organisms) makes it well suited to laboratory studies.…”

“…In addition, mycobacterial burden, usually assessed as grades of smear positivity (scanty, 1+2+, and 3+), is used to evaluate the infectiousness of cases in the context of public health contact tracing and screening [6], [7]. In translational research the need to accurately detect changes in M. tuberculosis burden is fundamental to the study of biologically meaningful immunological pathways, and drug and vaccine development in both human and murine models of disease.…”

Efficacy of real-time polymerase chain reaction for rapid diagnosis of endobronchial tuberculosis

“…6 The identification of M. tuberculosis in cultured specimens can take 6-8 weeks even when specimens are in good condition. 7 Since a delayed EBTB diagnosis can allow the disease to progress to substantial fibrostenosis and other morbidities, even with occasional anti-tuberculosis chemotherapy, 2 early diagnosis is critical.…”