Predicting tuberculosis among HIV-infected patients admitted to hospital: comparison of a model with clinical judgment of infectious disease specialists

Evaluation of clinical prediction rules for respiratory isolation of inpatients with suspected pulmonary tuberculosis

BACKGROUND

In the framework of hospital infection control, various clinical prediction rules (CPRs) for respiratory isolation of patients with suspected pulmonary tuberculosis (PTB) have been developed. Our aim was to evaluate their performance in an emergency department setting with a high prevalence of PTB.

METHODS

We searched the MEDLINE and OVID databases to identify CPRs to predict PTB. We used a previously collected database containing clinical, radiographical, and microbiological information on patients attending an emergency department with respiratory complaints, and we applied each CPR to every patient and compared the result with culture for Mycobacterium tuberculosis as the reference standard. We also simulated the proportion of isolated suspects and missed cases for PTB prevalences of 5% and 30%.

RESULTS

We withheld 13 CPRs for evaluation. We had complete data on 345 patients. Most CPRs achieved a high sensitivity but very low specificity and very low positive predictive value. Mylotte's score, which includes results of sputum smear as a predictive finding, was the best-performing CPR. It attained a sensitivity of 88.9% and a specificity of 63.9%. However, at a 30% PTB prevalence, 498 of 1000 individuals with suspected PTB would have to be isolated; 267 of these cases would be true PTB cases, and 33 cases would be missed. Two consecutive sputum smears had a sensitivity of 75.6% and a specificity of 99.7%.

CONCLUSIONS

In a setting with a high prevalence of PTB, only 1 of the 13 assessed CPRs demonstrated high sensitivity combined with satisfactory specificity. Our results highlight the need for local validation of CPRs before their application.

Derivation and validation of a clinical prediction score for isolation of inpatients with suspected pulmonary tuberculosis

BACKGROUND

The use of a clinical prediction score to improve the practice of instituting airborne-transmission precautions in patients with suspected tuberculosis holds promise for increasing appropriate isolation and decreasing unnecessary isolation. The objective of this study was to derive and validate a clinical prediction score for patients with suspected tuberculosis.

METHODS

We used a case-control study design to evaluate differences between patients with a diagnosis of tuberculosis and those placed under airborne precautions who had negative culture results. We developed risk scores based on a multivariable analysis of independently significant factors associated with tuberculosis. Subsequently, we evaluated the sensitivity and specificity of the score in a separate (validation) cohort of patients.

RESULTS

Within our population, we found 4 clinical factors associated with tuberculosis: chronic symptoms (odds ratio [OR], 10.2 [95% confidence interval {CI}, 2.95-35.4]), upper lobe disease on chest radiograph (OR, 5.27 [95% CI, 1.6-17.23]), foreign-born status (OR, 7.01 [95% CI, 2.1-23.8]), and immunocompromised state other than human immunodeficiency virus infection (OR, 8.14 [95% CI, 2.08-31.8]). Shortness of breath (OR, 0.13 [95% CI, 0.04-0.45]) was found to be associated with non-tuberculosis diagnoses and considered a negative predictor in the model. Using a cut-off point to maximize sensitivity, we applied the prediction rule to the validation cohort, resulting in a sensitivity of 97% and a specificity of 42%.

CONCLUSION

The tuberculosis prediction rule derived from our patient population could improve utilization of airborne precautions. Clinical prediction rules continue to show their utility for improvement in isolation practices in different demographic areas.

Clinical suspicion as a primary guidance to use commercial amplification tests for rapid diagnosis of pulmonary tuberculosis

The Abbott LCx (Abbott Park, IL) Mycobacterium tuberculosis complex is a commercial amplification assay discontinued from the European market in 2002. A prospective clinical study was carried out to evaluate the clinical utility of the above test as applied by specialists for the rapid diagnosis of active pulmonary tuberculosis (PTB). According to the physician's clinical judgment, patients were classified into 3 groups (low, intermediate, and high) aiming to estimate the probability of active disease. The gold standard for final diagnosis was based on microbiologic and clinical information including data from a 6-month follow-up period. Sensitivities and specificities of rapid microbiologic tests were compared with those based on an integrated approach including clinical evaluation plus the above tests. The incidence of PTB in 214 patients was 13.1%. The basis for initial treatment of PTB was smear-positive results in 46%, positive LCx results in 29%, and clinical suspicion in 18%. For the remaining 7%, therapy was started upon receipt of culture results. The sensitivity, specificity, and positive and negative predictive values of the LCx assay were 68%, 99%, 95%, and 95%, respectively. In comparison, they were 93%, 99%, 96%, and 99%, respectively, for the combination of clinical evaluation plus the LCx test. It is concluded that in patients with high-to-moderate pretest probabilities, the combination of clinical judgment and amplification results strongly enhances a rapid and correct diagnosis of PTB.

Tuberculosis, a re-emergent disease

Tuberculosis (TB) remains a major cause of morbidity and mortality worldwide. In Western Europe, regions with a high incidence of TB usually also have a high incidence of HIV infection; TB and HIV co-infection have increased over the past decade and among HIV infected patients, nearly half also develop TB. In settings where HIV is prevalent, TB drug resistance has also increased and several reports of TB and multi-drug resistant TB outbreaks, especially in health care settings, raise serious concerns about nosocomial transmission. Further research and new developments into more rapid diagnostic methods and sensitivity testing as well as the development of new anti-TB drugs are important to fight the disease. In addition, public health infrastructures have to be strengthened in order to increase adherence to TB treatment, where directly observed treatment strategy is the cornerstone for a successful outcome.

Determinants of health system delay among confirmed tuberculosis cases in Spain

BACKGROUND

Health system delay (HSD) is an important issue in tuberculosis (TB) control. This report investigates HSD and associated factors in a cohort of Spanish culture-confirmed TB patients.

METHODS

Data were collected from clinical records. Using logistic regression with two different cut-off points to define HSD (median and 75th percentile), adjusted odds ratios were used to estimate the association between HSD and different variables.

RESULTS

A total of 5184 culture-confirmed TB cases were included. Median and 75th percentile HSD were 6 and 25 days respectively. HSD significantly greater than the median was associated with: age >44 years, past or present intravenous drug use, diagnosis at a primary-care centre, prior preventive therapy, positive histology, request for drug-sensitivity testing, presence of silicosis or neoplasia in addition to TB, presence of non-TB related symptoms, and gastrointestinal site. HSD greater than the 75th percentile was related to the same variables, with the exception of diagnosis at a primary-care centre, positive histology, silicosis, non-TB-related symptoms and gastrointestinal site, for which the association disappeared; in contrast, an association with female gender emerged.

CONCLUSION

Despite free health care being universally available in Spain, there are some groups of TB patients whose treatment is unduly delayed.

Smear microscopy to diagnose tuberculosis early and prevent further transmission in a population with a high prevalence of HIV infection

In western Europe, Portugal has the highest incidence of tuberculosis (TB). The quickest way to diagnose TB is with a positive smear. To evaluate the usefulness of smear microscopy in a population with a high HIV seroprevalence, TB patients admitted during the year 2000 were retrospectively analyzed. Of the 74 TB patients admitted, 45 (61%) had pulmonary TB, 11 having multiresistant (MR)-TB. Considering that only half of the patients with pulmonary TB had a positive smear, a high degree of clinical suspicion is of great importance. Appropriate isolation facilities for TB are much needed, in order to prevent nosocomial TB spread.