Increased efficiency in evaluating patients with suspected tuberculosis by use of a dedicated airborne infection isolation unit

Clinical Impact of Nucleic Acid Amplification Testing in the Diagnosis of Mycobacterium Tuberculosis: A 10-Year Longitudinal Study

BACKGROUND

Nucleic acid amplification (NAA) testing for Mycobacterium tuberculosis (MTB) offers improved diagnostic accuracy, compared with smear microscopy, in differentiating MTB from other mycobacteria. We aimed to evaluate the reliability and projected impact of NAA testing in patients with acid-fast bacilli (AFB) smear-positive respiratory samples.

METHODS

We identified a retrospective cohort of all patients with AFB smear-positive respiratory specimens at Henry Ford Hospital from January 1, 2001 through December 31, 2011. We examined the association between patients' sociodemographic factors and clinical comorbidities with the likelihood of being diagnosed with MTB. We evaluated the projected change in duration of airborne isolation and unnecessary MTB treatment with introducing NAA testing into clinical decision making for AFB smear-positive patients.

RESULTS

One hundred thirty patients had AFB smear-positive respiratory specimens, 80 of these patients had a positive NAA test result, and 82 patients grew MTB on culture. Nucleic acid amplification testing had a sensitivity and specificity of 97.6% and 100%, respectively. Integrating NAA testing into clinical decision making for patients with AFB-positive smears was associated with a significantly shorter time in airborne isolation (6.0 ± 7.6 vs 23.1 ± 38.0, P < .001) and 9.5 ± 11.32 fewer days of unnecessary MTB treatment in patients with negative NAA test.

CONCLUSIONS

Nucleic acid amplification testing provided a rapid and accurate test in the diagnosis of MTB while significantly reducing the duration of isolation and unnecessary medications in patients with negative NAA test.

Impact of Infection Control Measures to Control an Outbreak of Multidrug-Resistant Tuberculosis in a Human Immunodeficiency Virus Ward, Peru

Multidrug-resistant tuberculosis (MDRTB) rates in a human immunodeficiency virus (HIV) care facility increased by the year 2000-56% of TB cases, eight times the national MDRTB rate. We reported the effect of tuberculosis infection control measures that were introduced in 2001 and that consisted of 1) building a respiratory isolation ward with mechanical ventilation, 2) triage segregation of patients, 3) relocation of waiting room to outdoors, 4) rapid sputum smear microscopy, and 5) culture/drug-susceptibility testing with the microscopic-observation drug-susceptibility assay. Records pertaining to patients attending the study site between 1997 and 2004 were reviewed. Six hundred and fifty five HIV/TB-coinfected patients (mean age 33 years, 79% male) who attended the service during the study period were included. After the intervention, MDRTB rates declined to 20% of TB cases by the year 2004 (P = 0.01). Extremely limited access to antiretroviral therapy and specific MDRTB therapy did not change during this period, and concurrently, national MDRTB prevalence increased, implying that the infection control measures caused the fall in MDRTB rates. The infection control measures were estimated to have cost US$91,031 while preventing 97 MDRTB cases, potentially saving US$1,430,026. Thus, this intervention significantly reduced MDRTB within an HIV care facility in this resource-constrained setting and should be cost-effective.

Diagnosis of tuberculosis by using a nucleic acid amplification test in an urban population with high HIV prevalence in the United States

Background

Use of nucleic acid amplification tests (NAAT) for the diagnosis of Mycobacterium tuberculosis (TB) has been recommended on respiratory specimens submitted for acid-fast bacilli (AFB) testing. It also helps distinguish between TB and non-tuberculous mycobacteria (NTM) species in a setting where NTM rates are relatively high. The purposes of this study are to describe the trend and characteristics of all AFB smear-positive respiratory samples that underwent amplified Mycobacterium tuberculosis direct (MTD) testing, a type of NAAT, and to evaluate the clinical utility and necessity of the test for diagnosis of TB in a population with high-HIV prevalence.

Methods

Prospective diagnostic testing and retrospective data analyses were conducted on all AFB smear-positive respiratory samples that underwent MTD testing from 2001 to 2011 at Grady Memorial Hospital (GMH), Atlanta, USA. The test performance was compared to culture.

Results

A total of 2,240 AFB smear-positive specimens from 1,412 patients were tested and analyzed in the study. The proportion of specimens that were culture-positive for TB was 28.5%. Sensitivity, specificity, positive predictive value, and negative predictive value of the MTD were 99.0%, 98.0%, 95.3% and 99.6%, respectively. A downward trend was observed in the yearly numbers as well as the proportions of MTD-positive specimens during the study period (p<0.01). There were 2,027 (90.5%) specimens from patients with known HIV status, of which 70.6% was HIV positive and the majority of them (81.8%) had CD4 counts of less than 200 cells/µL. HIV-positives were more likely to have NTM compared to HIV negatives (67.7% vs. 35.4%, p<0.01).

Conclusion

Despite the decrease in the incidence of TB, NAAT continues to be an accurate and important diagnostic test in a population with high HIV prevalence, and it differentiates TB and NTM organisms.

Xpert MTB/RIF assay shortens airborne isolation for hospitalized patients with presumptive tuberculosis in the United States

BACKGROUND

In the United States, individuals with presumptive pulmonary tuberculosis are placed in airborne infection isolation (AII) and assessed by smear microscopy on 3 respiratory specimens collected 8-24 hours apart. Xpert MTB/RIF assay (Xpert) on 1, 2, or 3 specimens may be more efficient for determining AII discontinuation.

METHODS

This single-center, observational cohort study of inpatients with presumptive pulmonary tuberculosis enrolled adults with 1 or more sputum specimens submitted for smear microscopy. Smear microscopy and Xpert were performed on each sputum specimen. Clinicians were blinded to Xpert results. The primary endpoint was AII duration. Secondary endpoints were laboratory processing time, strategy-based tuberculosis detection, and sensitivity and specificity.

RESULTS

Among 207 subjects, the median AII duration was 68.0 hours (interquartile range [IQR], 47.1-97.5) for smear microscopy compared with 20.8 hours (IQR, 16.8-32.0) for the 1-specimen Xpert, 41.2 hours (IQR, 26.6-54.8) for the 2-specimen Xpert, and 54.0 hours (IQR, 43.3-80.0) for the 3-specimen Xpert strategies (P ≤ .004). Median laboratory processing time for smear microscopy was 2.5 times as long as Xpert (P < .001). The 2- and 3-specimen Xpert and smear microscopy strategies captured all 6 tuberculosis cases. The 1-specimen Xpert strategy missed 1 case. No difference was observed between smear microscopy and Xpert in sensitivity or specificity for detection of Mycobacterium tuberculosis.

CONCLUSIONS

Xpert-based strategies significantly reduced AII duration compared with the smear-based strategy. The 2-specimen Xpert strategy was most efficient in minimizing AII time while identifying all tuberculosis cases among individuals with presumptive tuberculosis in this low-burden setting.

Cost analysis of a nucleic acid amplification test in the diagnosis of pulmonary tuberculosis at an urban hospital with a high prevalence of TB/HIV

INTRODUCTION

The Centers for Disease Control and Prevention has recommended using a nucleic acid amplification test (NAAT) for diagnosing pulmonary tuberculosis (TB) but there is a lack of data on NAAT cost-effectiveness.

METHODS

We conducted a prospective cohort study that included all patients with an AFB smear-positive respiratory specimen at Grady Memorial Hospital in Atlanta, GA, USA between January 2002 and June 2008. We determined the sensitivity, specificity, and positive and negative predictive value of a commercially available and FDA-approved NAAT (amplified MTD, Gen-Probe) compared to the gold standard of culture. A cost analysis was performed and included costs related to laboratory tests, hospital charges, anti-TB medications, and contact investigations. Average cost per patient was calculated under two conditions: (1) using a NAAT on all AFB smear-postive respiratory specimens and (2) not using a NAAT. One-way sensitivity analyses were conducted to determine sensitivity of cost difference to reasonable ranges of model inputs.

RESULTS

During a 6 1/2 year study period, there were 1,009 patients with an AFB smear-positive respiratory specimen at our public urban hospital. We found the NAAT to be highly sensitive (99.6%) and specific (99.1%) on AFB smear-positive specimens compared to culture. Overall, the positive predictive value (PPV) of an AFB smear-positive respiratory specimen for culture-confirmed TB was 27%. The PPV of an AFB smear-positive respiratory specimen for culture-confirmed TB was significantly higher for HIV-uninfected persons compared to those who were HIV-seropositive (152/271 [56%] vs. 85/445 [19%]; RR = 2.94, 95% CI 2.36-3.65, p<0.001). The cost savings of using the NAAT was $2,003 per AFB smear-positive case.

CONCLUSIONS

Routine use of the NAAT on AFB smear-positive respiratory specimens was highly cost-saving in our setting at a U.S. urban public hospital with a high prevalence of TB and HIV because of the low PPV of an AFB smear for culture-confirmed TB.

A national infection control evaluation of drug-resistant tuberculosis hospitals in South Africa

BACKGROUND

The importance of infection control (IC) in health care settings with tuberculosis (TB) patients has been highlighted by recent health care-associated outbreaks in South Africa.

OBJECTIVE

To conduct operational evaluations of IC in drug-resistant TB settings at a national level.

METHODS

A cross-sectional descriptive study was conducted from June to September 2009 in all multidrug-resistant (MDR-TB) and extensively drug-resistant TB (XDR-TB) facilities in South Africa. Structured interviews with key informants were completed, along with observation of IC practices. Health care workers (HCWs) were asked to complete an anonymous knowledge, attitudes and practices (KAP) questionnaire. Multilevel modeling was used to take into consideration the relationship between center and HCW level variables.

RESULTS

Twenty-four M(X)DR-TB facilities (100%) were enrolled. Facility infrastructure and staff adherence to IC recommendations were highly varied between facilities. Key informant interviews were incongruent with direct observation of practices in all settings. A total of 499 HCWs were enrolled in the KAP evaluation. Higher level of clinical training was associated with greater IC knowledge (P < 0.001), more appropriate attitudes (P < 0.001) and less time spent with coughing patients (P < 0.001). IC practices were poor across all disciplines.

CONCLUSION

These findings demonstrate a clear need to improve and standardize IC infrastructure in drug-resistant TB settings in South Africa.

Incidência de TB diagnosticada no pronto-atendimento de um hospital escola na região sudeste do Brasil

Neste trabalho, analisamos o número de casos de TB em um pronto-atendimento (PA) e o perfil de sensibilidade das cepas de Mycobacterium tuberculosis. Pacientes atendidos no Hospital das Clínicas, em Belo Horizonte (MG), foram selecionados. Entre 2002 e 2005, 240 pacientes com TB foram identificados. Destes, 117 (48,7%) foram diagnosticados no PA, 72 (61,5%) com baciloscopia positiva. Testes de sensibilidade foram realizados em 90 cepas, sendo 80 (89%) sensíveis, 9 (10%) resistentes e 1 (1%) multirresistente. A incidência de baciloscopia positiva e de TB resistente foi elevada, o que demanda uma adoção urgente de medidas de controle de TB no PA.

Control and prevention of healthcare-associated tuberculosis: the role of respiratory isolation and personal respiratory protection

Although the prevalence of tuberculosis continues to decline in most developed countries, the risk of healthcare-associated tuberculosis, remains for patients or healthcare staff. Outbreaks of healthcare-associated tuberculosis are usually associated with delays in diagnosis and treatment, or the care of patients in sub-optimal facilities. The control and prevention of tuberculosis in hospitals is best achieved by three approaches, namely administrative (early investigation diagnosis, etc.), engineering (physical facilities e.g. ventilated isolation rooms) and personal respiratory protection (face sealing masks which are filtered). Recent guidelines on the prevention of tuberculosis in healthcare facilities from Europe and the USA have many common themes. In the UK, however, negative pressure isolation rooms are recommended only for patients with suspected multi-drug resistant TB and personal respiratory protection, i.e. filtered masks, are not considered necessary unless multi-drug resistant TB is suspected, or where aerosol-generating procedures are likely. In the US, the standard of care for patients with infectious tuberculosis is a negative pressure ventilated room and the use of personal respiratory protection for all healthcare workers entering the room of a patient with suspected or confirmed tuberculosis. The absence of clinical trials in this area precludes dogmatic recommendations. Nonetheless, observational studies and mathematical modelling suggest that all measures are required for effective prevention. Even when policies and facilities are optimal, there is a need to regularly review and audit these as sometimes compliance is less than optimal. The differences in recommendations may reflect the variations in epidemiology and the greater use of BCG vaccination in the UK compared with the United States. There is a strong argument for advising ventilated facilities and personal respiratory protection for the care of all patients with tuberculosis, as multi-drug tuberculosis may not always be apparent on admission, and these measures minimise transmission of all cases of TB to other patients and healthcare staff.