Culture positivity of smear negative pulmonary and extrapulmonary tuberculosis- A study from North Kerala, India

Abstract

Introduction:The identification of smear negative pulmonary and extrapulmonary tuberculosis continues to remain a diagnostic challenge. This study was conducted in a tertiary care setup in north Kerala to isolate and identify mycobacteria by culture from radiologically and clinically suspected cases of smear negative pulmonary and extrapulmonary tuberculosis.Methods:A total of 200 samples (100 pulmonary and 100 extrapulmonary) were processed and cultured by automated (MB/BacT) and conventional methods. Heat stable catalase test, nitrate reduction test and detection of MPT 64 antigen were done to aid species identification.Results:Overall culture positivity was 7% (14 isolates - 8 pulmonary and 6 extrapulmonary) of which 92.9% (13) of the isolates were Mycobacterium tuberculosis and 7.1% (1) was Mycobacterium fortuitum (identified by molecular typing). Detection rate by automated method was 7% (14) and by conventional method was only 1.5% (3).Conclusion:Despite its shortcomings and low positivity, culture still remains the gold standard for the diagnosis of EPTB and SNPT. However, automated liquid cultures have better isolation rates than the conventional LJ culture. Subjecting these isolates to rapid diagnostic tests like antigen detection and LPA can aid in the early institution of appropriate treatment regimen.

A case report on recurrent subphrenic abscess with pulmonary tuberculosis

“…With references cited from various studies, since a positive culture for TB in extrapulmonary TB is very low, which can cause significant delay in initiation of treatment, our patient was started ATT with cytology of granulomatous inflammation which helped in decreasing the morbidity and mortality. 17,18 Review of various literatures revealed, a case report on 21 years old male with immunocompromised state and IgA deficiency with recurrent subdiaphragmatic collection as an unusual extrapulmonary manifestation of tuberculosis was reported for the first time in 2006. 1 Patient was hospitalised frequently for subphrenic abscess.…”

“…Cytology from pigtail site showed an inflammatory smear p/o granulomatous inflammation. 18 A positive culture for TB from intraperitoneal fluid is low and takes 6 to 8 weeks, which can cause significant delay in initiation of treatment, with expert opinion, patient was started on anti-tuberculous therapy. In 2 weeks, patient's abdomen pain, breathlessness, fever and pus discharge from sinus settled.…”

Efficacy of GeneXpert in Diagnosing Smear Negative Pulmonary Tuberculosis and Comparison to Culture

“…Direct and concentrated smears were prepared from clinical specimens by using modified Petroff's method [7]. Specimens were treated with 4 % NaOH for decontamination and digestion of clinical specimens.…”

“…It was reported that smear negative TB patients spread disease among 20% of total TB cases in the Republic of Congo [6]. Culture for MTB still stands as the most standardized test for definitive diagnosis but it considerably delays the results [7]. In high TB prevalent settings, suspected cases with at least two negative reports of sputum samples are given unspecified chemotherapeutic agents for 15 days and then advised for another sputum sample followed by a chest x-ray.…”

Accuracy of GeneXpert in Diagnosis of Smear Negative Tuberculosis: A Cross-Sectional Study

“…Diagnosis of TB is not possible without microbiological evidence while many patients remain with smear negative pulmonary TB (SNPT) for weeks and months further smear negative patients have been reported to spread TB among 20% cases [7]. Culture for MTB is considered as gold standard for sure diagnosis of TB which significantly delays the results due to number of reasons [8]. Similarly in cases with SNPT a complicated criterion is carried out for imperial treatment unless conclusive diagnosis is made which not only delays the standard treatment but also threatens in spread of disease to many healthy contacts [7].…”