Clinical and radiological data
Of the 121 patients, almost a quarter (n = 27) had a prior history of TB. Sixty percent (n = 73) were lifetime non-smokers. Two-thirds of patients (n = 79) had co-morbidities such as hypertension, diabetes mellitus, hyperlipidemia, ischemic heart disease, renal failure, malignancy or chronic lung disease. Twenty percent of these patients had three or more co-morbidities. Hypertension was the most common co-morbidity, followed by diabetes mellitus. Six patients were infected with HIV (Table
2).
Table 2
Clinical and radiological characteristics of 121 patients with AFB smear negative respiratory samples
Co-morbidities - no. (%#) | |
Previous history of TB | 27 (22.3) |
Current or ex-smoker | 48 (40) |
Hypertension | 28 (23.1) |
Diabetes mellitus | 23 (19) |
Hyperlipidemia | 19 (16.1) |
Ischemic heart disease | 15 (12.4) |
Renal failure | 13 (10.7) |
Chronic lung disease | 4 (3.3) |
Malignancy | 12 (9.9) |
HIV | 6 (4.9) |
Presenting Symptoms - no. (%#) | |
Cough | 40 (30.3) |
Fever | 20 (16.7) |
Anorexia | 14 (12) |
Loss of weight | 20 (16.3) |
Dyspnea | 17 (13.8) |
Hemoptysis | 9 (7.6) |
Radiological Findings - no.(%#) | |
Abnormal CXR | 116 (95.8) |
Consolidation | 40 (33) |
Nodules | 21 (17) |
Cavitation | 10 (8.2) |
Other abnormality* | 45 (37.2) |
Ninety percent of patients who were isolated were symptomatic - with more than half of these patients suffering from chronic cough or fever. Other symptoms included anorexia (27%), loss of weight (16.3%), dyspnea (13.8%) and hemoptysis (7.6%) (Table
2).
The median duration patients were symptomatic for any of the following: cough, fever, anorexia, loss of weight, dyspnea and hemoptysis, was two weeks (mean: 46 days, range: 1–365 days). Ninety-six percent of patients had an abnormal chest radiograph. The most common abnormality being consolidation in two-thirds (n = 40). Nodules were present in 17% (n = 21) and 37.2% (n = 45) had other abnormalities such as pleural effusion, interstitial infiltrates, granuloma, and mass lesions. Less than ten percent of patients had cavitatory lesions. Twelve percent (n = 15) of radiographs were reported as showing radiological changes suspicious of active PTB (Table
2).
Management and diagnosis
There were a total of 376 respiratory specimens collected from 121 patients. The most common respiratory sample obtained was sputum (63%), followed by laryngeal swabs (20%), BAL specimens (10%) and naso-gastric aspirates (7%). The mean and median number of smears for each patient was three. Thirty-six patients (30%) had four or more smears performed despite hospital protocol requiring only three samples. Twenty-four patients (20%) were de-isolated prematurely before the results of three negative AFB smears were obtained (Figure
1).
As to be expected, the mean duration of isolation was significantly shorter in patients who had fewer than three negative smears compared to those who had three or more negative smears (three days vs. five days, p <0.01). The overall mean cost of isolation to each patient was USD 1,440 (range: USD 290 - USD 5,510). The mean cost in patients who were de-isolated before three negative smears were obtained was USD 947 compared to USD 1,636 in those were only de-isolated after three negative smears (p <0.01).
Of the patients who followed hospital protocol requiring at least three negative smears before de-isolation, the mean duration from collection of the first smear to reporting of the third negative smear was 3.8 days (median: 3 days, range: 0–22 days). On average, the time taken from result of the third negative smear to de-isolation was 2.2 days but could range from as short as 0 to as long as 11 days. Thirty-two patients (26.4%) remained in isolation for more than 24 hours after the result of the third negative smear was made available.
A total of 20 out of 121 patients (16.5%) were subsequently diagnosed with PTB based on positive culture results for
M tuberculosis, despite having AFB smear-negative respiratory samples
. Half of these were from sputum samples, 35% from BAL fluid while the remaining 15% were from naso-gastric aspirate or laryngeal swabs (Figure
1).
Thirteen patients (10.7%) had PCR for M tuberculosis performed on their sputum or BAL samples at their managing physician’s discretion. Of these 13, four had positive PCR results (only two of these four patients subsequently had cultures that returned positive for TB).
Of the 20 patients who had positive TB culture results, 19 (95%) were symptomatic for cough, fever, hemoptysis, dyspnea, anorexia or loss of weight. This was compared to 88% (n = 89) of patients in the group who were culture negative. The difference however was not statistically significant. The median duration of symptoms was 21 days in the culture positive group and 14 days in the culture negative group (
p = 0.634). Twenty-five percent (n = 5) of culture positive patients had chest radiographs reported as being suspicious for active TB compared with ten percent (n = 10) of culture negative patients although this difference was not statistically significant. The mean duration of hospitalization was longer in patients with a positive culture although this did not reach statistical significance (18.4 versus 11.6 days,
p = 0.057). The mean cost incurred from utilization of isolation beds was significantly greater in those with a positive culture compared to those who were culture negative (USD 2624 versus USD 1727,
p < 0.01) (Table
3). This cost was computed directly from cost per day per room multiplied by total days spent in isolation room per patient.
Table 3
Comparison of TB culture positive and culture negative patients
Mean Age - yr | 58.4 | 60.9 | 0.525 |
Symptomatic* - no. (%) | 19 (95) | 89 (88.1) | 0.692 |
Median symptom duration - days | 21 | 14 | 0.634 |
CXR suggestive of active TB - no. (%) | 5 (25) | 10 (10) | 0.129 |
Mean length of hospitalization - days | 18.4 | 11.6 | 0.057 |
Mean cost of stay in isolation ward - USD | 2624 | 1727 | <0.01 |
Of the 24 patients who were de-isolated prematurely, three patients were subsequently diagnosed with PTB based on positive TB culture, giving an incidence of 12.5% TB positivity rate compared to 17.5% in the group who were de-isolated only after three negative AFB smears. None of the three patients had chest radiograph findings suspicious of active PTB.
Three patients died during their stay in isolation. All three patients had been diagnosed with PTB but none of the deaths were directly attributed to PTB.