Cross-reactivity of the IDEXX Legiolert method with other Gram-negative bacteria and waterborne pathogens leads to false-positive assay results.

Legionella species are the causative agent of Legionnaires' disease, a potentially fatal bacterial pneumonia. New regulations and standards have prioritized the development of water safety plans to minimize the growth and spread of Legionella species in buildings. To determine the presence and type of Legionella in a water system, microbiological culturing is the gold standard method. However, recently new methodologies have been developed that claim to be sensitive and specific for Legionella at the genus or L. pneumophila at the species level. Published and anecdotal reports suggest that one of these newer culture-based, enzyme-substrate methods, the IDEXX Legiolert test, may exhibit false positivity with other microbes common to water sources. We experimentally evaluated the IDEXX Legiolert method using these other waterborne bacteria including Elizabethkingia meningoseptica, Pseudomonas aeruginosa, Proteus mirabilis and Serratia marcescens at real-world environmental concentrations. We saw false-positive results for the Legiolert test with several of these organisms, at sample concentrations as low as 60 CFU per ml. False-positive Legionella results can trigger costly remediation and water-use restrictions, that may be implemented while waiting for additional, confirmatory microbiological testing that could, in this case, yield no L. pneumophila.

Simulation of Legionnaires' disease prospective spatiotemporal cluster detection, Allegheny County, Pennsylvania, USA.

Legionnaires' disease (LD) incidence in the USA has quadrupled since 2000. Health departments must detect LD outbreaks quickly to identify and remediate sources. We tested the performance of a system to prospectively detect simulated LD outbreaks in Allegheny County, Pennsylvania, USA. We generated three simulated LD outbreaks based on published outbreaks. After verifying no significant clusters existed in surveillance data during 2014-2016, we embedded simulated outbreak-associated cases into 2016, assigning simulated residences and report dates. We mimicked daily analyses in 2016 using the prospective space-time permutation scan statistic to detect clusters of ⩽30 and ⩽180 days using 365-day and 730-day baseline periods, respectively. We used recurrence interval (RI) thresholds of ⩾20, ⩾100 and ⩾365 days to define significant signals. We calculated sensitivity, specificity and positive and negative predictive values for daily analyses, separately for each embedded outbreak. Two large, simulated cooling tower-associated outbreaks were detected. As the RI threshold was increased, sensitivity and negative predictive value decreased, while positive predictive value and specificity increased. A small, simulated potable water-associated outbreak was not detected. Use of a RI threshold of ⩾100 days minimised time-to-detection while maximizing positive predictive value. Health departments should consider using this system to detect community-acquired LD outbreaks.

Paradox of serial interferon-gamma release assays: variability width more important than specificity size.

SETTING: Serial screening for latent tuberculous infection (LTBI) is commonly performed in certain populations, such as health care workers. The high apparent conversion rate in some studies of interferon-gamma release assays is puzzling given the claimed high specificity of these tests. OBJECTIVE: To understand how test-retest variability, specificity, and underlying LTBI prevalence affect observed outcomes of repeated testing for LTBI. DESIGN: Mathematical model assuming constant test sensitivity and specificity over time and no new infections. RESULTS: Test-retest variability had a large effect on the observed proportion of conversions (initial negative test, followed by a positive test) and reversions (initial positive test, followed by a negative test). For example, a test with 70% specificity and 5% test-retest variability would be associated with a conversion rate of 3.7% and a reversion rate of 7.7%, while a test with 95% specificity but 10% test-retest variability would be associated with a conversion rate of 5.5% and a reversion rate of 57%, assuming that both tests are 80% sensitive and underlying LTBI prevalence was 5%. CONCLUSION: Test-retest variability is a key parameter that should be reported for tests used for serial screening for LTBI. Reducing test-retest variability can reduce false-positive and false-negative results.

Tackling the unknowns of short-course rifapentine-based treatment for active tuberculosis: a decision analysis.

BACKGROUND: Shorter treatment regimens for tuberculosis (TB) are deemed vital for advancing TB control. Murine studies have suggested potential new regimens; however, Phase II human studies of these drug combinations have not shown clear improvement in 2-month culture conversion over current therapy. Nevertheless, drugs such as rifapentine (RPT) may have additional sterilizing effects after 2 months that are difficult to measure in current Phase II studies. OBJECTIVES: To model potential bactericidal effects of RPT in a Phase III trial of a 4-month anti-tuberculosis regimen. METHODS: We developed a Markov model of anti-tuberculosis treatment to compare two regimens for treating TB: a 6-month standard (rifampin-based) treatment and a 4-month regimen using high-dose RPT. The primary outcome was the number of relapses. RESULTS: In the base-case scenario, standard therapy resulted in fewer relapses; improvement in 2-month culture conversion rates in the RPT arm did not change this result. However, while RPT has better sterilizing ability during months 3 and 4 (as observed in the mouse model), the 4-month regimen results in fewer relapses. CONCLUSIONS: Higher 2-month culture conversion rates are neither sufficient nor necessary for making a theoretical 4-month anti-tuberculosis treatment regimen advantageous.

Medium matters: modeling the impact of solid medium performance on tuberculosis trial sample size requirements.

SETTING: Two-month solid medium culture conversion is a commonly used, if suboptimal, endpoint for phase 2 anti-tuberculosis treatment trials. OBJECTIVE AND DESIGN: To model the effect of the performance characteristics (sensitivity and contamination rate) of solid medium on required sample size for a two-arm clinical trial with 85% true (gold standard) culture conversion in the control and 95% in the experimental arm. RESULTS: Increasing sensitivity and decreasing contamination reduced the sample size from 239 subjects/arm (60% sensitivity, 30% contamination) to 138 subjects/arm (95% sensitivity, 1% contamination). CONCLUSION: Optimizing solid medium has significant potential to reduce sample size and increase the efficiency of tuberculosis clinical trials.

Should all patients undergoing treatment with biologic agents be screened annually for latent tuberculosis infection with an interferon gamma release assay?

Systemic biologic therapy has become commonplace for the treatment of a variety of inflammatory dermatologic conditions, particularly psoriasis. Screening for latent tuberculosis infection (LTBI) is recommended prior to initiation of systemic biologic agents, and an interferon gamma release assays (IGRA) is often used as the screening modality. Annual screening for LTBI is also recommended for patients while on systemic biologic therapy, but the literature does not clearly support how often screening should be performed. In addition, serial testing with IGRAs, particularly among low-risk populations without any new tuberculosis (TB) exposures, has proven to be unreliable with frequent reversions and conversions. We propose that in low-incidence TB regions, repeat LTBI screening should only be considered for patients on systemic biologic therapy if any new TB exposures occurred since initial LTBI screening was performed prior to starting biologic therapy. This strategy aims to reduce false-positive LTBI testing that can expose patients to hazardous antibiotics and result in the unnecessary interruption of systemic biologic therapy.

The complexities of Xpert® MTB/RIF interpretation.

The Xpert(®) MTB/RIF assay has demonstrated robust capability for diagnosing tuberculosis (TB) and rifampin (RMP) resistance. Optimal use of Xpert in diverse settings will require knowledge of challenges when interpreting the results. We present three selected cases from the United States, a low-burden TB setting, to highlight important clinical scenarios encountered with Xpert testing: rapid RMP resistance detection in a patient with pre-extensively drug-resistant TB who immigrated from the Philippines, false-positive RMP resistance detection, and Mycobacterium tuberculosis detection in a culture-negative patient. These cases demonstrate that a low pre-test probability of TB or drug-resistant TB can complicate the interpretation of the Xpert assay.

Advances in the management of pulmonary disease due to Mycobacterium abscessus complex.

Mycobacterium abscessus complex is a group of rapidly growing mycobacteria, and an emerging cause of non-tuberculous mycobacterial lung disease in patients with cystic fibrosis and chronic lung diseases, such as bronchiectasis. M. abscessus complex is the most drug-resistant of the mycobacterial pathogens, resulting in limited therapeutic options and a high treatment failure rate. M. abscessus complex is comprised of three closely related subspecies: M. abscessus (sensu stricto), M. massiliense and M. bolletii. M. abscessus encodes a functional erythromycin ribosomal methylase gene, erm(41), which modifies the binding site for macrolide antibiotics, causing inducible macrolide resistance. However, this inducible macrolide resistance is not seen in M. massiliense, as the erm(41) gene of this subspecies is non-functional. Accordingly, treatment success rates with macrolide-based antibiotic treatment are much higher in patients with M. massiliense infections than in those infected with M. abscessus. Precise speciation of M. abscessus complex is important for predicting antibiotic susceptibilities and patient outcome.

Hepatitis B core antibody-positive donors in cardiac transplantation: a single-center experience.

Hepatitis B virus (HBV) core antibody (HBcAb)-positive donors are increasingly utilized in solid organ transplantation. We report a single center's experience in cardiac transplantation with 18 HBcAb-positive donors. Available follow-up on recipients of cardiac allografts from HBcAb-positive donors, including 2 donors with low-level serum HBV DNA at the time of transplantation, demonstrated no documented donor-derived HBV transmission.

Public health costs for tuberculosis suspects in Wake County, North Carolina, United States.

SETTING: As the incidence of tuberculosis (TB) declines in high-income countries, resources to control TB are also declining. A portion of these resources are utilized for the evaluation and treatment of persons initially suspected of, but who do not actually have, TB (TB suspects). OBJECTIVE: To describe the cost of TB suspects to public health departments, and determine whether part of this cost can be averted using improved diagnostic tools. DESIGN: We evaluated resource utilization for all TB suspects as well as a random sample of TB cases managed at the Wake County public health clinic during 2008-2010. The proportion of total health department costs attributable to TB suspects was estimated. A sensitivity analysis assessed the potential impact of a rapid, accurate diagnostic test to avert suspect-associated costs. RESULTS: Of 135 patients evaluated for TB, 36 (27%) were suspects, accounting for 14% (US5,885) of the total estimated costs for managing all patients. A perfect diagnostic test with a 3-day turnaround would have averted US27,975 (53%) of the costs attributable to suspects. CONCLUSION: A substantial proportion of public health resources is utilized to manage persons whose final diagnosis is not TB. Efficient implementation of novel rapid tests could avert substantial public health costs.

Increased prevalence of advanced tuberculosis in rural low tuberculosis caseload counties in North Carolina.

SETTING: Pulmonary tuberculosis (TB) patients reported in North Carolina (NC), USA, from 1996 to 2008 (inclusive). OBJECTIVE: To compare prevalence of cavitary TB as a surrogate marker for advanced disease in low-caseload counties with high-caseload counties. DESIGN: A multivariate log binomial regression model was used to estimate prevalence ratios (PRs) for cavitary TB. RESULTS: The proportion of TB cases in low-caseload counties vs. the total number of TB cases in NC over the study period increased from 10% in 1996 to 20% in 2008. After adjusting for human immunodeficiency virus (HIV) status, excess alcohol use and report year, patients in rural areas of low-caseload counties had greater prevalence (PR 1.40, 95%CI 1.19-1.64) of cavitary disease compared with patients from rural areas of high-caseload counties. The prevalence of cavitary TB did not differ between urban residents of high- or low-caseload counties (PR 1.00, 95%CI 0.86-1.16) after adjusting for HIV status, excess alcohol use and report year. DISCUSSION: TB patients in rural areas of low-caseload counties presented with more advanced TB disease compared with patients from urban and/or high-caseload counties. Barriers to timely recognition of TB in rural low-caseload settings must be considered in TB control programs.

Did the 'Great Recession' produce a depression in tuberculosis incidence?

In 2009, the United States experienced a record drop in its tuberculosis (TB) case rate, coinciding with a major economic downturn. To investigate this relationship, we modeled short-term changes in gross domestic product, unemployment, and immigration as predictors of TB incidence. We also correlated each state's 2009-2010 change in unemployment with its 2008-2009 change in TB incidence. Although economic factors did not explain the decline, the 2009-2010 change in unemployment negatively correlated with incidence. We hypothesize that factors related to increased unemployment, such as diagnostic delay, may have played a role in the sudden drop in TB case rates.

Mortality before or during treatment among tuberculosis patients in North Carolina, 1993-2003.

SETTING: North Carolina, United States. OBJECTIVE: To investigate the demographic and behavioral risk factors associated with death among tuberculosis (TB) patients in North Carolina. DESIGN: Retrospective cohort of all TB patients reported in North Carolina, 1993-2003 (inclusive). A surveillance dataset based upon Report of Verified Case of Tuberculosis (RVCT) records was cross-linked with the National Death Index (NDI) to confirm date of death and capture additional deaths. RESULTS: Among 5311 TB patients, 181 died before initiation of TB treatment, and 540 died before completion of TB treatment. Increasing age, miliary/meningeal disease, and human immunodeficiency virus (HIV) infection were associated with increased risk of death before treatment, during early treatment (initial 8 weeks) and later in TB treatment. In addition to these factors, excess alcohol use (HR 1.62, 95%CI 1.13-2.32) and residence in a nursing home (HR 1.65, 95%CI 1.20-2.29) were associated with a significantly increased risk of death during the first 8 weeks of treatment. CONCLUSION: Many of the deaths in TB patients occurred in the most vulnerable populations, such as the elderly or those with HIV infection, and may be attributable to delayed diagnosis and poor functional status.

Aspergillus niger: an unusual cause of invasive pulmonary aspergillosis.

Infections due to Aspergillus species cause significant morbidity and mortality. Most are attributed to Aspergillus fumigatus, followed by Aspergillus flavus and Aspergillus terreus. Aspergillus niger is a mould that is rarely reported as a cause of pneumonia. A 72-year-old female with chronic obstructive pulmonary disease and temporal arteritis being treated with steroids long term presented with haemoptysis and pleuritic chest pain. Chest radiography revealed areas of heterogeneous consolidation with cavitation in the right upper lobe of the lung. Induced bacterial sputum cultures, and acid-fast smears and cultures were negative. Fungal sputum cultures grew A. niger. The patient clinically improved on a combination therapy of empiric antibacterials and voriconazole, followed by voriconazole monotherapy. After 4 weeks of voriconazole therapy, however, repeat chest computed tomography scanning showed a significant progression of the infection and near-complete necrosis of the right upper lobe of the lung. Serum voriconazole levels were low-normal (1.0 microg ml(-1), normal range for the assay 0.5-6.0 microg ml(-1)). A. niger was again recovered from bronchoalveolar lavage specimens. A right upper lobectomy was performed, and lung tissue cultures grew A. niger. Furthermore, the lung histopathology showed acute and organizing pneumonia, fungal hyphae and oxalate crystallosis, confirming the diagnosis of invasive A. niger infection. A. niger, unlike A. fumigatus and A. flavus, is less commonly considered a cause of invasive aspergillosis (IA). The finding of calcium oxalate crystals in histopathology specimens is classic for A. niger infection and can be helpful in making a diagnosis even in the absence of conidia. Therapeutic drug monitoring may be useful in optimizing the treatment of IA given the wide variations in the oral bioavailability of voriconazole.

The value of end-of-treatment chest radiograph in predicting pulmonary tuberculosis relapse.

SETTING: Patients with cavitary pulmonary tuberculosis (TB) on baseline chest radiograph (CXR) who remain culture-positive after 8 weeks of treatment are at high risk of relapse. The role of end-of-treatment (EOT) CXR in predicting relapse is unclear. OBJECTIVE: To determine whether EOT CXR independently predicts TB relapse. DESIGN: We conducted a secondary analysis of a randomized trial of intermittent treatment using rifapentine in the continuation phase of TB treatment among 1004 human immunodeficiency virus seronegative adults with culture-proven pulmonary TB. RESULTS: Relapse occurred in 17.3% of subjects with persistent cavity on EOT CXR, in 7.6% of subjects with a cavity that resolved by EOT, and 2.5% (P=0.002 for trend) of subjects who never had a cavity. In multivariable analysis, patients with persistent cavity on EOT CXR were significantly more likely to relapse than patients with no cavity on baseline or 2-month CXR (hazard ratio [HR] 4.22, 95%CI 2.00-8.91), and were more likely to relapse than subjects whose early cavity had resolved by EOT CXR (HR 1.92, 95%CI 1.09-3.39). CONCLUSION: A persistent cavity after 6 months of TB treatment was independently associated with disease relapse after controlling for other variables. EOT CXR may help predict those likely to relapse.

Effect of flow regimes on the presence of Legionella within the biofilm of a model plumbing system.

AIMS: Stagnation is widely believed to predispose water systems to colonization by Legionella. A model plumbing system was constructed to determine the effect of flow regimes on the presence of Legionella within microbial biofilms. METHODS AND RESULTS: The plumbing model contained three parallel pipes where turbulent, laminar and stagnant flow regimes were established. Four sets of experiments were carried out with Reynolds number from 10,000 to 40,000 and from 355 to 2,000 in turbulent and laminar pipes, respectively. Legionella counts recovered from biofilm and planktonic water samples of the three sampling pipes were compared with to determine the effect of flow regime on the presence of Legionella. Significantly higher colony counts of Legionella were recovered from the biofilm of the pipe with turbulent flow compared with the pipe with laminar flow. The lowest counts were in the pipe with stagnant flow. CONCLUSIONS: We were unable to demonstrate that stagnant conditions promoted Legionella colonization. SIGNIFICANCE AND IMPACT OF THE STUDY: Plumbing modifications to remove areas of stagnation including deadlegs are widely recommended, but these modifications are tedious and expensive to perform. Controlled studies in large buildings are needed to validate this unproved hypothesis.

Tuberculosis knowledge and attitudes among physicians who treat young children in North Carolina, USA.

SETTING: North Carolina, USA. OBJECTIVE: To understand physicians' knowledge and attitudes toward the treatment of young children with latent tuberculosis infection (LTBI) in a low-incidence region. DESIGN: Cross-sectional survey of 525 pediatricians and 525 family practitioners in North Carolina. RESULTS: Of 1050 surveys mailed, 149 (14%) were returned. In the previous year, 96% of responding physicians had treated children who had emigrated from a tuberculosis (TB) endemic country. During the last 2 years, 84% of physicians had not diagnosed any young children with TB disease, and 46% had not treated any young children with LTBI. Most (83%) physicians routinely placed tuberculin skin tests (TSTs), and 26% reported placing > 10 TSTs per month. Experience in treating children with LTBI was the only predictor of TB knowledge. Physicians were particularly confused about two issues: 1) TST among bacille Calmette-Guérin (BCG) vaccinated children and 2) treatment of young children with recent exposure to an adult with infectious TB. CONCLUSIONS: Knowledge of important issues related to management of LTBI in children aged < 5 years was limited among physicians in an area with relatively low TB incidence. Creative methods must be developed to help physicians in low-incidence areas to appropriately diagnose and treat LTBI among young children.

Risk factors for infective endocarditis in patients with enterococcal bacteremia: a case-control study.

BACKGROUND: Based on previous studies, enterococcal infective endocarditis (IE) is considered a unimicrobial, community-acquired disease of older Caucasian men. PATIENTS AND METHODS: We evaluated the relationship between enterococcal bacteremia and IE by comparing clinical and demographic characteristics of all cases of enterococcal IE within an 8-year period (n = 41) with controls randomly chosen from patients with enterococcal bacteremia without IE. RESULTS: By univariate and multivariable analyses, the presence of a prosthetic valve (PV) and infection with Enterococcus faecalis were significantly associated with IE, while age, gender, race, polymicrobial infection and community-acquired infection were not. Almost an equal number of women and men had enterococcal IE. Cases of enterococcal IE were commonly nosocomial (39%) and polymicrobial (17%). CONCLUSIONS: Enterococcal endocarditis can no longer be considered exclusively a unimicrobial, community-acquired disease of Caucasian men. Instead, our data suggest that the presence of a PV and infection by E. faecalis are associated with an increased risk for IE.