Magnitude of Mycobacterium tuberculosis transmission among household and non-household contacts of TB patients

<sec id="st1"> <title>SETTING</title> The household and non-household contacts of patients with tuberculosis (TB) face varying degrees of risk of infection by Mycobacterium tuberculosis. </sec> <sec id="st2"> <title>OBJECTIVE</title> To quantify new infection and to determine the risk factors associated with new infection among named contacts in San Francisco, CA, USA. </sec> <sec id="st3"> <title>DESIGN</title> We performed a cohort study in patients with culture-positive pulmonary TB. We analyzed patient, contact, environmental and bacterial characteristics. </sec> <sec id="st4"> <title>RESULTS</title> Of the 2422 contacts named by 256 patients, 149 (6.2%) had new infection due to recent transmission from 79 (30.9%) patients. Of the 149 new infections, 87 (58.4%) occurred among household contacts and 62 (41.6%) among non-household contacts. Numerous acid-fast bacilli in sputum (odds ratio [OR] 2.64, 95%CI 1.32-5.25) and contacts being named by more than one patient (OR 2.90, 95%CI 1.23-6.85) were associated with new infection among household contacts. Being older than 50 years (OR 1.93, 95%CI 1.09-3.41) and an Asian/Pacific Islander (OR 3.09, 95%CI 1.50-6.37) were associated with new infection among non-household contacts. </sec> <sec id="st5"> <title>CONCLUSIONS</title> Fewer than one third of patients caused new infection to his/her contacts. A substantial proportion of transmission resulting in new infection occurred outside of the household. The risk factors for infection among household and non-household contacts are different and should be considered when prioritizing control interventions. </sec>.

Interplay of strain and race/ethnicity in the innate immune response to M. tuberculosis

Background

The roles of host and pathogen factors in determining innate immune responses to M. tuberculosis are not fully understood. In this study, we examined host macrophage immune responses of 3 race/ethnic groups to 3 genetically and geographically diverse M. tuberculosis lineages.

Methods

Monocyte-derived macrophages from healthy Filipinos, Chinese and non-Hispanic White study participants (approximately 45 individuals/group) were challenged with M. tuberculosis whole cell lysates of clinical strains Beijing HN878 (lineage 2), Manila T31 (lineage 1), CDC1551 (lineage 4), the reference strain H37Rv (lineage 4), as well as with Toll-like receptor 2 agonist lipoteichoic acid (TLR2/LTA) and TLR4 agonist lipopolysaccharide (TLR4/LPS). Following overnight incubation, multiplex assays for nine cytokines: IL-1β, IL-2, IL-6, IL-8, IL-10, IL-12p70, IFNγ, TNFα, and GM-CSF, were batch applied to supernatants.

Results

Filipino macrophages produced less IL-1, IL-6, and more IL-8, compared to macrophages from Chinese and Whites. Race/ethnicity had only subtle effects or no impact on the levels of IL-10, IL-12p70, TNFα and GM-CSF. In response to the Toll-like receptor 2 agonist lipoteichoic acid (TLR2/LTA), Filipino macrophages again had lower IL-1 and IL-6 responses and a higher IL-8 response, compared to Chinese and Whites. The TLR2/LTA-stimulated Filipino macrophages also produced lower amounts of IL-10, TNFα and GM-CSF. Race/ethnicity had no impact on IL-12p70 levels released in response to TLR2/LTA. The responses to TLR4 agonist lipopolysaccharide (TLR4/LPS) were similar to the TLR2/LTA responses, for IL-1, IL-6, IL-8, and IL-10. However, TLR4/LPS triggered the release of less IL-12p70 from Filipino macrophages, and less TNFα from White macrophages.

Conclusions

Both host race/ethnicity and pathogen strain influence the innate immune response. Such variation may have implications for the development of new tools across TB therapeutics, immunodiagnostics and vaccines.

Impact of Euro-American sublineages of Mycobacterium tuberculosis on new infections among named contacts

BACKGROUND

The impact of demographic, clinical, and bacterial factors on new infection by Euro-American lineage Mycobacterium tuberculosis among contacts of patients with tuberculosis (TB) has not been evaluated.

OBJECTIVE

To describe the risk factors for new infection by Euro-American M. tuberculosis sublineages in San Francisco, California.

DESIGN

We included contacts of patients with TB due to Euro-American M. tuberculosis. Sublineages were determined by large-sequence polymorphisms. We used tuberculin skin testing or QuantiFERON®-TB Gold In-Tube to identify contacts with new infection. Regression models with generalized estimating equations were used to determine the risk factors for new infection.

RESULTS

We included 1488 contacts from 134 patients with TB. There were 79 (5.3%) contacts with new infection. In adjusted analyses, contacts of patients with TB due to region of difference 219 M. tuberculosis sublineage were less likely to have new infection (OR 0.23, 95%CI 0.06-0.84) than those with other sublineages. Other risk factors for new infection were contacts exposed to more than one patient with TB, contacts exposed for 30 days, or contacts with a history of smoking or excessive alcohol consumption.

CONCLUSIONS

In addition to well-known exposure and clinical characteristics, bacterial characteristics independently contribute to the transmissibility of TB in San Francisco.

Clinical and bacteriological characteristics associated with clustering of multidrug-resistant tuberculosis

SETTING

The impact of the genetic characteristics of Mycobacterium tuberculosis on the clustering of multidrug-resistant tuberculosis (MDR-TB) has not been analyzed together with clinical and demographic characteristics.

OBJECTIVE

To determine factors associated with genotypic clustering of MDR-TB in a community-based study.

DESIGN

We measured the proportion of clustered cases among MDR-TB patients and determined the impact of clinical and demographic characteristics and that of three M. tuberculosis genetic characteristics: lineage, drug resistance-associated mutations, and rpoA and rpoC compensatory mutations.

RESULTS

Of 174 patients from California and Texas included in the study, the number infected by East-Asian, Euro-American, Indo-Oceanic and East-African-Indian M. tuberculosis lineages were respectively 70 (40.2%), 69 (39.7%), 33 (19.0%) and 2 (1.1%). The most common mutations associated with isoniazid and rifampin resistance were respectively katG S315T and rpoB S531L. Potential compensatory mutations in rpoA and rpoC were found in 35 isolates (20.1%). Hispanic ethnicity (OR 26.50, 95%CI 3.73-386.80), infection with an East-Asian M. tuberculosis lineage (OR 30.00, 95%CI 4.20-462.40) and rpoB mutation S531L (OR 4.03, 95%CI 1.05-23.10) were independent factors associated with genotypic clustering.

CONCLUSION

Among the bacterial factors studied, East-Asian lineage and rpoB S531L mutation were independently associated with genotypic clustering, suggesting that bacterial factors have an impact on the ability of M. tuberculosis to cause secondary cases.

Reduced sensitivity of the QuantiFERON(®) test in diabetic patients with smear-negative tuberculosis

SETTING

Immunosuppressive conditions have been associated with low sensitivity of interferon-gamma release assays (IGRAs) and the tuberculin skin test (TST) for the diagnosis of tuberculosis (TB). However, no systematic analysis of patient and bacterial characteristics has been performed before.

OBJECTIVE

To determine the sensitivity and the risk factors for false-negative QuantiFERON(®)-TB (QFT) assay and TST in TB patients.

DESIGN

We performed a retrospective analysis of data collected in a community-based study of TB in San Francisco, CA, USA. We included 300 TB patients who underwent QFT and TST.

RESULTS

The risk factors for false-negative QFT were human immunodeficiency virus infection and the use of QuantiFERON(®)-TB Gold. In patients with sputum smear-negative TB, diabetes mellitus (DM) was associated with false-negative QFT (OR 2.85, 95%CI 1.02-7.97, P = 0.045). TST sensitivity was higher than QFT sensitivity in DM patients (OR 9.46, 95%CI 2.53-35.3).

CONCLUSIONS

In San Francisco, QFT sensitivity was lower than that of TST, especially in patients with DM. Stratified analysis by sputum smear results showed that this association was specific to smear-negative TB. In contrast, TST was not affected by the presence of DM.

Sublineages of lineage 4 (Euro-American) Mycobacterium tuberculosis differ in genotypic clustering

SETTING

Mycobacterium tuberculosis is classified into six phylogenetic lineages, each of which can be divided into sublineages. Sublineages of the same lineage have phenotypic differences, including their capacity to cause disease (pathogenicity).

OBJECTIVE

1) To test the hypothesis that different sublineages of lineage 4, which causes most of the tuberculosis (TB) in the United States, have varying ability to cause secondary cases as determined by genotypic clustering, a proxy for pathogenicity; and 2) to determine if spoligotype and mycobacterial interspersed repetitive units (MIRU) typing could infer sublineage.

DESIGN

We included TB cases caused by lineage 4 strains from our community-based study in San Francisco. Sublineage was determined by regions of difference. Genotypic clustering was determined by insertion sequence 6110 and polymorphic guanine-cytosine-rich sequence. Associations between sublineages and patient characteristics were evaluated with adjusted and unadjusted analyses.

RESULTS

The most frequent sublineage was H37Rv-like. In the adjusted analysis, sublineage 183 was associated with clustering and homelessness. We found that strains from different sublineages had convergent spoligotype and MIRU types.

CONCLUSIONS

Sublineage 183 is associated with genotypic clustering, evidence of its being more able to cause secondary cases than the other lineage 4 sublineages. This finding suggests that bacterial factors contribute to the pathogenesis of TB. Spoligotype and MIRU type cannot be used to infer sublineage.

Differences among sublineages of the East-Asian lineage of Mycobacterium tuberculosis in genotypic clustering

SETTING

The East-Asian lineage of Mycobacterium tuberculosis is composed of five sublineages, and includes the strains from the Beijing spoligotype family. In some studies these strains were highly pathogenic, although other studies did not support this finding.

OBJECTIVE

To determine if the sublineages of the East-Asian lineage of M. tuberculosis differ in their capacity to cause secondary cases, as assessed by genotypic clustering of isolates.

DESIGN

In a population-based study of 545 patients with M. tuberculosis from the East-Asian lineage in San Francisco, we used DNA-based fingerprinting to identify genotypic clustering, which was compared among the different sublineages defined by large sequence polymorphism.

RESULTS

Strains from sublineage 207 had the highest frequency of genotypic clustering. In the multivariate analysis, only patients born in the United States were associated with clustering.

CONCLUSIONS

We found evidence in a univariate analysis that the different East-Asian sublineages of M. tuberculosis have different frequencies of genotypic clustering. The effect size for this difference was unchanged in multivariate analysis, although loss of observations due to missing data resulted in a non-significant P value. It is tantalizing to hypothesize that the different East-Asian sublineages may differ in their capacity to cause secondary cases.

Predicting mortality from HIV-associated Pneumocystis pneumonia at illness presentation: an observational cohort study

BACKGROUND

Although the use of antiretroviral therapy has led to dramatic declines in AIDS-associated mortality, Pneumocystis pneumonia (PCP) remains a leading cause of death in HIV-infected patients.

OBJECTIVES

To measure mortality, identify predictors of mortality at time of illness presentation and derive a PCP mortality prediction rule that stratifies patients by risk for mortality.

METHODS

An observational cohort study with case note review of all HIV-infected persons with a laboratory diagnosis of PCP at San Francisco General Hospital from 1997 to 2006.

RESULTS

451 patients were diagnosed with PCP on 524 occasions. In-hospital mortality was 10.3%. Multivariate analysis identified five significant predictors of mortality: age (adjusted odds ratio (AOR) per 10-year increase, 1.69; 95% CI 1.08 to 2.65; p = 0.02); recent injection drug use (AOR 2.86; 95% CI 1.28 to 6.42; p = 0.01); total bilirubin >0.6 mg/dl (AOR 2.59; 95% CI 1.19 to 5.62; p = 0.02); serum albumin <3 g/dl (AOR 3.63; 95% CI 1.72-7.66; p = 0.001); and alveolar-arterial oxygen gradient >or=50 mm Hg (AOR 3.02; 95% CI 1.41 to 6.47; p = 0.004). Using these five predictors, a six-point PCP mortality prediction rule was derived that stratifies patients according to increasing risk of mortality: score 0-1, 4%; score 2-3, 12%; score 4-5, 48%.

CONCLUSIONS

The PCP mortality prediction rule stratifies patients by mortality risk at the time of illness presentation and should be validated as a clinical tool.