Feasibility of shortening isolation of TB-suspects by first-sample PCR

Research output: Contribution to conferencePosterResearch

Rationale: Isolation of patients suspected for tuberculosis (TB) is usually guided by serial sputum smears. Many of patients initially isolated will turn out not to have TB, or will not be regarded as contagious. Current standards imply isolation for hours or days until contagiousness has been excluded.
Objective: To evaluate the utility of single-specimen polymerase chain-reaction (PCR) for Mycobacterium tuberculosis complex (MTBC) as a parameter to cease isolation when negative.
Methods: We evaluated all patients in Denmark who had sputa investigated for MTBC at the National Reference Laboratory for Mycobacteriology, Statens Serum Institut, Denmark, through a 10-year period (2002-2011). We identified all MTBC-culture positive patients, and included those who had at least 3 sputa investigated within 14 days around the first MTBC-culture positive specimen, and who had at least one of the specimens PCR-analyzed for MTBC. We selected the first specimen with a PCR-result, and the next 2 specimens (regardless of PCR) within the 14-day window. From these, we identified the number of patients having at least one smear-positive specimen and a negative first PCR result.
Results: We included 53,533 sputa from 20,927 patients. In 4,208 samples, MTB was detected by culture, representing 1,637 patients. 858 of these patients had minimum 3 sputa analyzed within 14 days. Of these, 473 patients had at least one specimen analyzed by PCR. Overall, 342 (72.3%) had positive microscopy, and 372 (78.6%) had a positive PCR result on the first specimen. 12 patients (3.5 % (1.6;5.5) of smear-positive patients) had smear-positive, PCR-negative results. Of the 12 patients, 10 (83.3%) were smear positive on 1 of 3 specimens, 7 (58.3%) with a low-grade smear. 2 patients had 2 smear-positive samples. None were smear-positive on the sample that produced the PCR-negative result.

Conclusion: Though adequate sensitivity in diagnosing TB still requires serial samples for microbiological examination, the question of isolation can be determined by first-sample PCR in the majority of cases, when the test is negative. In our study, less than 4% of smear-positive patients would have been released from isolation if determined by first-sample PCR, the majority only producing one low-grade smear, thereby representing a smaller risk of transmission. Our results are laboratory specific and cannot be transferred to other labs as the results are influenced by PCR vs culture specimen volume and PCR-sensitivity. In addition, submission of 3 sputa is crucial for a definitive culture-based diagnosis, detection of NTM, drug susceptibility testing, and MTB-subtyping.
Original languageEnglish
Publication year2014
Publication statusPublished - 2014
EventAmerican Thoracic Society 2014 International Conference - San Diego Convention Center, San Diego, CA, United States
Duration: 16 May 201421 May 2014

Conference

ConferenceAmerican Thoracic Society 2014 International Conference
LocationSan Diego Convention Center
CountryUnited States
CitySan Diego, CA
Period16/05/201421/05/2014

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