Assessing learner engagement with virtual educational events: Development of the Virtual In-Class Engagement Measure (VIEM)

BACKGROUND

The COVID-19 pandemic has necessitated virtual education, but effects on learner engagement are unknown. We developed a virtual in-class engagement measure (VIEM) to assess learner engagement in online surgical education events.

METHODS

Using the STROBE, an observer collected tool to document student engagement, as a template an ASE committee workgroup developed the VIEM. The VIEM had two parts: observer assessment and learner self-assessment of engagement. Trained observers collected engagement data from two institutions using the VIEM. Surgical attendings, fellows and residents were observed during virtual learning events. Educator attitudes towards online teaching were also assessed via survey.

RESULTS

22 events with 839 learners were observed. VIEM distinguished between sessions with low and high engagement. 20% of learners pretended to participate. Half of instructors were comfortable with virtual teaching, but only 1/3 believed was as effective as in-person. 2/3 of teachers believed video learners were more engaged than audio learners.

CONCLUSIONS

Virtual platforms do not automatically translate into increased engagement. Standard tools such as VIEM may help with assessment of engagement during virtual education.

Suitability of Estimated Glomerular Filtration Rate for Live Kidney Donor Selection

INTRODUCTION

The assessment of the glomerular filtration rate (GFR) in kidney donor candidates is required for determining donor candidate acceptability. This assessment can be done using an estimated GFR (eGFR) or a measured GFR (mGFR). The primary objective of the present study was to compare, in healthy adult kidney donor candidates, GFR measured by the clearance of iothalamate to GFR estimated using the Chronic Kidney Disease Epidemiology Collaboration equation and to determine if eGFR was a suitable stand-alone assessment. A secondary objective was to explore demographic factors that affect the relationship of the eGFR and the mGFR.

METHODS

A retrospective review of kidney donor candidates' records at the J. C. Walter, Jr., Transplant Center, Houston Methodist Hospital, from January 2013 to March 2016 was undertaken. GFR was measured by the plasma clearance of radioisotopic iothalamate and estimated using the Chronic Kidney Disease Epidemiology Collaboration equation.

RESULTS

The median mGFR was 108 mL/min/1.73 m². The eGFR underestimated the mGFR by 11.5%. The underestimation was greatest in subjects with an mGFR of ≥90 mL/min/1.73 m². The eGFR overestimated the mGFR in donor candidates of black race.

CONCLUSIONS

The Chronic Kidney Disease Epidemiology Collaboration eGFR can be used for screening potential kidney donors restricting the use of iothalamate (mGFR) to those donors with an eGFR below the transplant centers' acceptable GFR threshold for donation, thereby effecting cost savings and greater donor convenience. The eGFR in black donor candidates should be used with caution.

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.

Yield of chest radiograph in tuberculosis screening for HIV-infected persons at a district-level HIV clinic

SETTING

An Hoa Clinic, a district-level human immunodeficiency virus (HIV) clinic in Ho Chi Minh City, Viet Nam.

OBJECTIVE

To assess the performance of chest radiograph (CXR) in screening for pulmonary tuberculosis (PTB) among HIV-infected individuals and identify misdiagnosed opportunities.

DESIGN

This cross-sectional study was conducted in 397 HIV-infected patients consecutively enrolled at the An Hoa Clinic in Ho Chi Minh City, Viet Nam, from August 2009 to June 2010. The performance of CXR in TB screening was assessed based on its sensitivity, specificity, positive likelihood ratio and negative likelihood ratio.

RESULTS

Symptom screening alone missed 50% of PTB cases. The combination of CXR and symptom screening yielded an additional 28.6% (8/28) in PTB screening as compared with symptom screening alone, and should be applied routinely, especially in high TB prevalent settings.

CONCLUSION

CXR is a good predictor for PTB even in HIV-infected individuals. The combination of CXR and screening for common TB symptoms considerably improved the sensitivity of detecting active PTB in people living with HIV. If available, routine sputum culture and the World Health Organization-endorsed Xpert(®) MTB/RIF assay should be implemented to achieve a more accurate diagnosis.

Characteristics and costs of multidrug-resistant tuberculosis in-patient care in the United States, 2005-2007

OBJECTIVE

A population-based study of 135 multidrug-resistant tuberculosis (MDR-TB) patients reported to the Centers for Disease Control and Prevention (CDC) during 2005-2007 found 73% were hospitalized. We analyzed factors associated with hospitalization.

METHODS

We assessed statistically significant multivariable associations with US in-patient TB diagnosis, frequency of hospitalization, length of hospital stay, and in-patient direct costs to the health care system.

RESULTS

Of 98 hospitalized patients, 83 (85%) were foreign-born. Blacks, diabetics, or smokers were more likely, and patients with disseminated disease less likely, to receive their TB diagnosis while hospitalized. Patients aged ⩾65 years, those with the acquired immune-deficiency syndrome (AIDS), or with private insurance, were hospitalized more frequently. Excluding deaths, length of stay was greater for patients aged ⩾65 years, those with extensively drug-resistant TB (XDR-TB), those residing in Texas, those with AIDS, those who were unemployed, or those who had TB resistant to all first-line medications vs. others. Average hospitalization cost per XDR-TB patient (US$285 000) was 3.5 times that per MDR-TB patient (US$81 000), in 2010 dollars. Hospitalization episode costs for MDR-TB rank third highest and those for XDR-TB highest among the principal diagnoses.

CONCLUSIONS

Hospitalization was common and remains a critical care component for patients who were older, had comorbidities, or required complex management due to XDR-TB. MDR-TB in-patient costs are among the highest for any disease.

Mycobacterium tuberculosis bacteraemia: experience from a non-endemic urban centre

The isolation of Mycobacterium tuberculosis from blood culture specimens has been associated with human immunodeficiency virus (HIV) co-infection with variable impact on tuberculosis (TB) mortality reported. The overwhelming majority of M. tuberculosis bacteraemia cases were described in developing countries. We present a nested case-control analysis of clinical, sociodemographic and behavioural risk factors in patients with positive M. tuberculosis blood cultures compared with patients with negative blood cultures from a 9-year population-based active TB surveillance study conducted in Houston, Texas. There were 42 patients with M. tuberculosis bacteraemia, 47 blood culture negative patients and 3573 patients for whom no mycobacterial blood culture was requested. HIV infection was more common in patients for whom a mycobacterial blood culture was requested (79.8% versus 15.1% p <0.001). Of the patients with M. tuberculosis bacteraemia, six were HIV negative or had no documentation of HIV status, including five with immunosuppressive conditions other than HIV. Patients with M. tuberculosis bacteraemia were more likely than patients with negative blood cultures to be deceased at diagnosis or to die while on TB therapy (50.0% versus 17.0%, p <0.01), to report men-who-have-sex-with-men behaviour (31.7% versus 13.0%, p 0.03), to have renal failure (28.6% versus 6.4%, p 0.01), and to have HIV RNA levels higher than 500 000 copies/mL (61.9% versus 17.2%, p ≤0.01). Requests for mycobacterial culture of blood specimens were more common in HIV-infected individuals, and the presence of M. tuberculosis bacteraemia was associated with a significant increase in mortality.

Can mycobacterial katG genetic changes in isoniazid-resistant tuberculosis influence human disease features?

BACKGROUND

Isoniazid-resistant (INHr) Mycobacterium tuberculosis isolates often have katG mutations, and katG is a virulence factor in animal models. It is unclear if katG mutations or other mutations influence the characteristics of human disease.

OBJECTIVE

To determine if the presence of INHr-conferring mutations were associated with distinct clinical features of tuberculosis (TB).

METHODS

In a retrospective case-control study, INHr-conferring mutations were determined by DNA sequencing. We examined associations between clinical characteristics in patients with INHr M. tuberculosis (stratified by groups of relevant INHr-conferring mutations, including katG-S315T and inhA-C(-)15T mutations) and pan-susceptible (PS) isolates.

RESULTS

Twenty-nine INHr TB cases and 50 PS controls were evaluated. Disease characteristics were not statistically different between INHr and PS cases. However, patients infected with non-katG mutants were associated with a higher rate of sputum culture conversion at 1 month after adjustment for relevant covariates (adjusted OR [aOR] 4.4, 95%CI 1.1-23.6, P = 0.04). Patients infected with katG mutants were associated with a higher rate of unilateral disease (aOR 4.7, 95%CI 1.0-34.3, P = 0.05).

CONCLUSIONS

Most INHr TB cases with non-katG mutations have disease associated with faster response to treatment, and most cases with katG mutants have localized lung involvement.

Population-based surveillance of extensively drug-resistant tuberculosis in Shandong Province, China

To investigate the prevalence of extensively drug-resistant tuberculosis (XDR-TB) in Chinese populations, we analyzed the drug resistance profiles of 1787 Mycobacterium tuberculosis isolates through a population-based surveillance project in Shandong Province, China. We found 330 (18.5%; 95%CI 16.1-20.3) isolates resistant to ≥1 first-line drug and 65 (3.6%; 95%CI 2.9-4.6) multidrug-resistant (MDR) isolates, of which 13 (20.0%; 95%CI 11.9-31.4) were XDR; 47/65 MDR-TB isolates (70.8%; 95%CI 58.2-81.4) were resistant to fluoroquinolones. Our results indicate that inadequate application of second-line anti-tuberculosis drugs has caused increased prevalence of XDR-TB in certain Chinese populations.

Low agreement between the T-SPOT®.TB assay and the tuberculin skin test among college students in China

T-SPOT®.TB and the tuberculin skin test (TST) were used to screen for latent tuberculosis infection among 899 Chinese college students. The positivity rates for T-SPOT®.TB and TST were respectively 13.0% (95% confidence interval [CI] 10.4-15.9) and 24.9% (95%CI 21.5-28.6) among students with a bacille Calmette-Guérin (BCG) scar (agreement of both tests 72.3%; 95%CI 68.6-75.8; κ = 0.118), and respectively 17.3% (95%CI 11.7-24.2) and 23.7% (95%CI 17.3-31.2) among those without a BCG scar (agreement 73.1%; 95%CI 65.4-79.9; κ = 0.179). These results demonstrate low agreement between the TST and T-SPOT.TB in the Chinese population studied.

Tuberculosis infection in drug users: interferon-gamma release assay performance

SETTING

An inner city neighborhood in Houston, Texas, known for a high rate of drug use.

OBJECTIVE

To determine the prevalence of latent tuberculosis infection (LTBI) using the QuantiFERON-TB Gold (QFT-G) test, the TSPOT.TB test and the tuberculin skin test (TST) in drug users and to evaluate the performance of the QFT-G and TSPOT.TB tests vs. the TST.

DESIGN

Cross-sectional study. Bivariate and multivariate logistic regression analyses were used to determine risks associated with each test outcome.

RESULTS

The prevalence of LTBI in 119 drug users studied was 28% by TST and 34% by QFT-G and T-SPOT.TB. Kappa statistics indicated fair to moderate concordance between QFT-G and TSPOT.TB vs. TST. About one-fifth of the population that tested negative with TST was positive with either QFT-G or T-SPOT.TB. On multivariate analysis, the likelihood of testing QFT-positive or T-SPOT.TB-positive increased by 8% and 6%, respectively, for every year of age; TST positivity was associated with smoking crack at home; being Caucasian or having a history of alcohol use was positively associated with a positive T-SPOT.TB test.

CONCLUSION

Interferon-gamma release assays (IGRAs) are superior to the TST in drug users with a higher prevalence of LTBI. Future studies need to assess the predictive value of IGRAs on the progression from LTBI to active TB in high-risk populations.

Community outreach with weekly delivery of anti-retroviral drugs compared to cognitive-behavioural health care team-based approach to improve adherence among indigent women newly starting HAART

Sustained virological suppression requires adherence to >95% of doses of therapy. Overall there is paucity of data on adherence interventions among women and post-intervention outcomes. In this pilot study, we evaluated a novel strategy of weekly delivery of medications (Directly Delivered Therapy: DDT) for six months using an outreach worker (ORW), among ARV naïve indigent women starting HAART and compared the 'during intervention' and 'post-intervention' outcomes to the health care team (a nurse educator, a case worker, a pharmacist and social worker/drug addictions counsellor) based approach termed Adherence Coordination Services (ACS) and the Standard of Care (SoC) historical referent group. The baseline characteristics of the three groups were comparable. The proportion of women who achieved sustained virologic suppression in 4-8 month period for DDT; ACS and SoC groups were 86% (18/21); 54% (6/11); and 36% (8/22) (P<0.004); and in the 10-14 month period were 80% (12/15); 54% (6/11) and 45%(10/22) (P=0.036 for DDT vs. SoC). Retention rate in the DDT was 87%, and 92% of 307 ORW visits were kept, and post-intervention satisfaction was high. Short-term weekly delivery of medications using a community based liaison is a feasible, acceptable and a cost-effective strategy for improving both short-term and perhaps long-term adherence among women initiating their first HAART regimen.

No association between the +874T/A single nucleotide polymorphism in the IFN-gamma gene and susceptibility to TB

A single nucleotide polymorphism (SNP), +874T/A, in the first intron of the interferon-gamma (IFN-gamma) gene, has presented associations with human susceptibility to tuberculosis (TB) in some ethnic populations, but not in others. In this population-based case-control study with adult TB patients from Houston, Texas, we found no significant differences of + 874T/A genotypic frequencies between cases and ethnically-matched controls or between advanced forms of TB disease (extra-pulmonary involvement or presence of cavitary disease) and pulmonary TB. Given possible sample size limitations, our results suggest that the IFN-gamma +874T/A mutation has no association with TB susceptibility or TB disease severity.

Determinants of sustained virological suppression in indigent, HIV-infected patients: is single protease inhibitor-based antiretroviral therapy truly highly active?

BACKGROUND

Effective virological suppression with HAART is dependent on strict adherence to therapy. Compliance with therapy is influenced by clinical and psychosocial factors.

METHOD

We performed a retrospective study investigating determinants of effective virological suppression, defined as <400 RNA at 11-13 months of HAART, in an urban indigent population. The study included 366 new patients presenting for care to the Thomas Street Clinic, Houston, Texas, between April and December 1998. Median age, CD4 count, and viral load (VL) of the study population were 37.5 years, 189 cells/mm(3), and 53,000, respectively. Thirty-nine percent had AIDS, 20% had cocaine-positive drug screens, and 64% were antiretroviral naïve. Two hundred and sixty-seven patients were started on HAART. Thirty-four percent showed virological suppression.

RESULTS

In multivariate analysis, adherence to HAART, care by experienced primary provider, baseline VL <100,000 copies/mL, age >35 years, and no active substance use were associated with virological suppression. Rates of virological suppression with HAART are unacceptably low in this urban indigent population.

CONCLUSION

Low rates of virological suppression are primarily due to lack of adherence rather than late utilization of care among ethnic minorities. Single protease-inhibitor-based antiretroviral therapy does not appear to be highly active in this patient population.

Recurrent tuberculosis in Houston, Texas: a population-based study

OBJECTIVE

To determine the predictors of recurrence of tuberculosis (TB), the drug resistance pattern of Mycobacterium tuberculosis strains recovered from recurrent TB patients, and the frequency of re-infection with a new M. tuberculosis strain among patients with recurrent disease.

DESIGN

A population-based, retrospective case-control study using the Houston Tuberculosis Initiative database.

RESULTS

We found that, among 100 patients with recurrent TB who completed adequate therapy for a first episode of TB, not receiving directly observed therapy, pulmonary disease, HIV/AIDS diagnosis, not having a family physician, being unemployed and using public transportation were predictors of recurrent disease. There was a significant increase in drug-resistant M. tuberculosis strains in the second episode of disease compared to the first episode (21.3% vs. 8.2%, P = 0.04). Exogenous re-infection with a new strain of M. tuberculosis was found to cause 24-31% of recurrent TB.

CONCLUSION

Recurrent TB in Houston is associated with a significant increase in drug-resistant M. tuberculosis strains. Re-infection with a new M. tuberculosis strain causes a significant proportion of recurrent TB in an area of low TB incidence. Patients with HIV/AIDS constitute a population at increased risk of disease recurrence.

Extra-pulmonary manifestations in a large metropolitan area with a low incidence of tuberculosis

BACKGROUND

The increases in extra-pulmonary tuberculosis (EPTB) have been largely due to human immunodeficiency virus co-infection. The rates of EPTB have remained constant despite the decline in pulmonary tuberculosis (PTB) cases.

OBJECTIVE

To evaluate covariates associated with EPTB.

METHODS

A 4-year cohort of EPTB patients was compared with PTB cases. Enrollees were assessed for TB risk, medical records were reviewed, and Mycobacterium tuberculosis isolates were fingerprinted.

RESULTS

We identified 538 EPTB cases (28.6%) in a total of 1878 enrollees. The most common sites of infection were lymph nodes (43%) and pleura (23%). EPTB cases included 320 (59%) males, 382 (71%) patients were culture-positive, and 332 (86.9%) patient isolates were fingerprinted. Fewer EPTB than PTB patients belonged to clustered M. tuberculosis strains (58% vs. 65%; P = 0.02). A multivariate model identified an increased risk for EPTB among African Americans (OR = 1.9, P = 0.01), HIV-seropositive (OR = 3.1, P < 0.01), liver cirrhosis (OR = 2.3, P = 0.02), and age <18 years (OR = 2.0, P = 0.04). Patients with concomitant pulmonary and extra-pulmonary infections were more likely to die within 6 months of TB diagnosis (OR = 2.3, P < 0.01).

CONCLUSIONS

African American ethnicity is an independent risk factor for EPTB. Mortality at 6 months is partly due to the dissemination of M. tuberculosis and the severity of the underlying co-morbidity.

Extrathoracic tuberculosis lymphadenitis in adult HIV seronegative patients: a population-based analysis in Houston, Texas, USA

OBJECTIVE

To evaluate the covariates associated with extrathoracic tuberculosis lymphadenitis (ETBL) among adult HIV-seronegative patients.

METHODS

Enrollees were interviewed for TB risk assessment, their medical records were reviewed, and their Mycobacterium tuberculosis isolates underwent molecular characterization. Between 1 October 1995 and 30 September 1999, HIV-negative patients with ETBL were compared with other HIV-negative TB patients.

RESULTS

We identified 73 ETBL cases (5%) out of a total of 1371 adult HIV-negative enrollees. Significant variables predicting ETBL in the univariate analysis included age < 45 years, female sex, Asian ethnicity, foreign birth, BCG vaccination, and infection with a M. tuberculosis isolate identified in major genetic group 1. Further analysis by birth country revealed increased ETBL risk for persons from countries other than the Americas and with a TB incidence > 25 per 100 000 per year. The multivariate model demonstrated increased risk for ETBL for patients of female sex (OR = 2.6, P < 0.01) and birth in Africa or South-east Asia (OR = 4.8; P = 0.03 and OR = 33.6; P = 0.01, respectively).

CONCLUSIONS

In adult HIV-negative patients, ETBL occurs more frequently in females and in immigrants from countries other than the Americas; persons from India, South-east Asia and the Eastern Mediterranean exhibited the highest risk among these regions.

Role of frozen section, sex, age and tumour size in differentiating follicular adenoma from carcinoma: a meta-analysis

Background

Frozen section (FS) has been the mainstay of intraoperative decision-making in thyroid neoplasms for many years. However, since the widespread use of preoperative fine-needle aspiration, the need for FS in patients with follicular neoplasms (FNs) has been debated. Preoperative features may be better at distinguishing follicular carcinoma (FC) from adenoma (FA). One reason why these issues are unresolved is because clinical studies are often too small to reach statistical significance. The purpose of this study was to combine modern trials and use the technique of meta-analysis to determine the efficacy of FS and the role of sex, age and tumour size in patients with FNs.

Methods

Inclusion criteria were published and unpublished studies between 1990 and 1999 inclusive, in which patients had a permanent pathology (PP) diagnosis of FA or FC (including Hurthle cell tumours) and underwent FS or had clinical features recorded. A pooled sample of the combined data was analysed for the prognostic variables and outcomes. P &lt; 0·05 was considered significant.

Results

Nineteen studies were included. FS was evaluated in 11 studies (n = 2204). FS matched PP in 82 per cent of patients and was considered helpful. FS was indeterminate in 13 per cent of cases and was considered unhelpful. FS was detrimental in 4 per cent of patients. In 27 per cent of FCs, FS reported FA (false negative) and in 1 per cent of FAs, FS reported FC (false positive). Overall, FS had an 87 per cent sensitivity, 48 per cent specificity, 92 per cent positive predictive value, 35 per cent negative predictive value and 82 per cent accuracy. Clinical features were examined in ten studies (n = 1980). Nine studies (n = 1780) reported sex; 20 per cent of patients were male. A disproportionately high percentage of patients with FC were male (28 per cent) compared with female (P &lt; 0·001). Two studies (n = 548) reported age; 36 per cent of patients were over 50 years old. A disproportionately high percentage of patients with FC were aged over 50 years (52 per cent) compared with those younger than 50 years (P &lt; 0·001). Six studies (n = 1620) reported tumour size; 19 per cent of FNs were larger than 3–5 cm. A disproportionately high percentage of FCs were larger than 3–5 cm (33 per cent) compared with smaller lesions (P &lt; 0·001).

Conclusion

FS is able to differentiate FC from FA in over 80 per cent of patients. It has a false-positive rate of less than 1 per cent and therefore may be trusted most when it reports a FC. In cases in which FS reports FA, male sex, age greater than 50 years and tumour size larger than 3–5 cm can be used as indicators that a FN will be a FC.

Laparoscopic ventral hernia repair during the learning curve

Large series of laparoscopic ventral hernia repair have shown excellent results. However, published comparative studies have had conflicting outcomes. We retrospectively reviewed the first 29 laparoscopic ventral hernia repairs performed at a VA Medical Center from January 2000 to June 2001. The outcome was compared to that of open repairs performed during the same time period. Outcomes between the groups were similar in all respects, except for the length of stay. The conversion rate for the laparoscopic approach was 13.8%. There was one death in the laparoscopic group due to an unrecognized enterotomy. There were three recurrences in the open group and one in the laparoscopic group with a mean follow up of 13 months. In our series, laparoscopic hernia repair resulted in a shorter hospital stay but no other significant benefits, along with a risk of missed enterotomy. The risk-benefit ratio for this procedure may be high during the learning curve.

5' dinucleotide repeat polymorphism of NRAMP1 and susceptibility to tuberculosis among Caucasian patients in Houston, Texas

SETTING

Houston Tuberculosis Initiative (HTI) and Baylor College of Medicine, Houston, Texas.

OBJECTIVE

To further explore the association between the polymorphisms of NRAMP1 and human susceptibility/resistance to tuberculosis (TB), specifically to determine whether the reported association shown for blacks and Asians holds true for Caucasian populations.

DESIGN

In a case-control study, 135 adult Caucasian TB patients and 108 adult Caucasian HIV-seronegative non-TB controls were analyzed for the association between the polymorphisms in NRAMP1 gene and clinical TB.

RESULTS

Heterozygote at 5'(GT)n, a dinucleotide repeat polymorphism in the promoter of NRAMP1, was observed at significantly higher frequencies among HIV-negative patients with pulmonary TB (41.6%; OR 2.02; 95%CI 1.11-3.64), extra-pulmonary TB (66.7%; OR 4.80; 95%CI 1.34-17.15), and HIV-seropositive TB patients (50%; OR 3.77; 95%CI 1.33-10.66) in comparison with the controls (27.8%). Homozygotes (GT)(10,10) were over-represented among HIV-positive TB patients (18.2%; OR 6.86; 95%CI 1.55-30.21) compared to the controls (5.5%).

CONCLUSION

These findings suggest that the 5'(GT)n polymorphism of NRAMP1 modifies TB susceptibility in this Caucasian population, and could possibly be related to the site of infection among HIV-negative individuals and HIV-coinfected TB.

The contribution of ethnicity to Mycobacterium tuberculosis strain clustering

OBJECTIVE

Descriptive study of molecular epidemiologic patterns of tuberculosis cases among ethnic minorities in Houston, Texas.

DESIGN

Population-based, prospective, active surveillance, and molecular epidemiology study.

PATIENTS

Tuberculosis cases reported to the City of Houston Tuberculosis Control Office between October 1995 and September 1998.

RESULTS

During the study period, 1,139 culture-positive patients were enrolled for whom isolates of their culture specimen were available. Of these, 910 were part of an ethnic minority. Molecular characterization identified 689 of 1,139 isolates to be clonally related. Factors significantly associated with tuberculosis strain clustering in a multivariable logistic regression analysis were: birth in the United States, a history of homelessness, infection with the human immunodeficiency virus (HIV), pulmonary disease, infection with a tuberculosis strain from principal genetic group 1 or 3, living in a residence with five or more persons present, and use of public transportation more than once weekly. Asian ethnicity and increasing age were associated with decreased odds of clustering.

CONCLUSIONS

Ethnicity was not a significant covariate for strain clustering after adjustments for factors related to socio-economic status.

Treatment of isoniazid-resistant tuberculosis in southeastern Texas

BACKGROUND

Isoniazid-resistant tuberculosis (INHr-TB) can be treated successfully with several treatment regimens. However, the optimal regimen and duration are unclear.

STUDY OBJECTIVE

To analyze the efficacy of treatment regimens used for INHr-TB in the southeastern Texas region.

DESIGN

Retrospective cohort study.

SETTING

Health-care facilities reporting tuberculosis (TB) patients in the Houston and Tyler areas.

SUBJECTS

All patients reported to have INHr-TB from 1991 to 1998. Exclusion criteria included poor compliance, additional first-line drug-resistance (except aminoglycosides), and death before completion of 1 month of treatment.

MEASUREMENTS AND RESULTS

Main treatment outcomes were treatment failure, relapse, and TB-related death. Fifty-three of 83 patients were included in the study; aminoglycoside resistance coexisted in 37.5% of isolates. Seven types of treatment regimens were identified. Eighteen patients (34%) received rifampin, pyrazinamide, and ethambutol thrice weekly for 9 months. Four patients (7.5%) had a total effective treatment duration of < 9 months. Thirty patients (56.6%) and 16 patients (30.2%) received thrice-daily and daily treatment regimens, respectively. Forty-nine patients achieved sputum conversion. Treatment failure and death occurred in one patient (1.9%). Three patients (5.7%) experienced relapses. There was a significant difference in total effective treatment time between patients with and without relapses (8.3 +/- 1.1 months vs 11.1 +/- 2.1 months; p < 0.02). Twice-weekly treatment regimens were associated with relapse (p = 0.05).

CONCLUSIONS

Several treatment regimens were prescribed for INHr-TB in southeastern Texas. INHr-TB treatment durations were > 7 months, and treatment regimen efficacy was adequate. Twice-weekly treatment was associated with relapse, whereas thrice-weekly and daily treatments performed similarly. A prospective study with different treatment durations is needed to determine the optimal treatment regimen for patients with INHr-TB.

Networks and tuberculosis: an undetected community outbreak involving public places

After decades of decline in developed countries, there was a resurgence of tuberculosis in the mid-1980s accompanied by increased recognition that this infectious disease has long remained a major public health problem at the global level. New methods from molecular biology, in particular DNA 'fingerprinting' (of Mycobacterium tuberculosis), made it clear that current transmission and recent infection (in contrast to reactivation of earlier, latent infection) were much more significant than previously believed. Studies of tuberculosis outbreaks using these new tools pointed to complex networks through which infection was spreading and highlighted the need for new approaches to outbreak investigation and disease control. In the study reported here a new approach--combining methods from molecular biology, epidemiology and network analysis--was used to examine an outbreak of tuberculosis in Houston, Texas. Initial investigation using conventional strategies revealed few contacts among 37 patients with identical (six-band) DNA (IS6110-based) fingerprints but subsequent research uncovered over 40 places (including many gay bars) to which patients in this outbreak could be linked. Network methods were used to reconstruct an outbreak network and to quantify the relative importance (here, 'betweenness' centrality) of different actors (persons and places) playing a role in the outbreak. The multidisciplinary work provides the basis for a new approach to outbreak investigation and disease control.

Identification and characterization of a second extracellular collagen-like protein made by group A Streptococcus: control of production at the level of translation

A recent study found that group A Streptococcus (GAS) expresses a cell surface protein with similarity to human collagen (S. Lukomski, K. Nakashima, I. Abdi, V. J. Cipriano, R. M. Ireland, S. R. Reid, G. G. Adams, and J. M. Musser, Infect. Immun. 68:6542-6553, 2000). This streptococcal collagen-like protein (Scl) contains a long region of Gly-X-X motifs and was produced by serotype M1 GAS strains. In the present study, a second member of the scl gene family was identified and designated scl2. The Scl2 protein also has a collagen-like region, which in M1 strains is composed of 38 contiguous Gly-X-X triplet motifs. The scl2 gene was present in all 50 genetically diverse GAS strains studied. The Scl2 protein is highly polymorphic, and the number of Gly-X-X motifs in the 50 strains studied ranged from 31 in one serotype M1 strain to 79 in serotype M28 and M77 isolates. The scl1 and scl2 genes were simultaneously transcribed in the exponential phase, and the Scl proteins were also produced. Scl1 and Scl2 were identified in a cell-associated form and free in culture supernatants. Production of Scl1 is regulated by Mga, a positive transcriptional regulator that controls expression of several GAS virulence factors. In contrast, production of Scl2 is controlled at the level of translation by variation in the number of short-sequence pentanucleotide repeats (CAAAA) located immediately downstream of the GTG (Val) start codon. Control of protein production by this molecular mechanism has not been identified previously in GAS. Together, the data indicate that GAS simultaneously produces two extracellular human collagen-like proteins in a regulated fashion.

Epidemiologic differences between United States- and foreign-born tuberculosis patients in Houston, Texas

The proportion of foreign-born tuberculosis patients in the United States is increasing. To analyze the epidemiology of tuberculosis in foreign-born people, culture-positive patients with tuberculosis in Houston, Texas, were interviewed from October 1995 through September 1998, and their isolates were molecularly characterized. Of the 1131 patients included in the study, 795 (70.3%) were US born and 336 (29.7%) were foreign born. The decrease in tuberculosis case rate among US-born people was 3.5 times that of foreign-born people. Significantly more US-born than foreign-born patients belonged to strain clusters (71.3% vs. 29.5%; P<.001). Risk factors associated with strain clustering were as follows: black ethnicity, low income, and homelessness in US-born patients and homelessness in foreign-born patients. Isolates from foreign-born patients were more likely to be resistant to >/=1 drug (15.4% vs. 8.4%; P=.001) and to be multidrug resistant (2.4% vs. 0.7%; P=.027) than isolates from US-born patients. These observations warrant increased emphasis on this distinct subpopulation of tuberculosis patients.

Transmission dynamics and molecular characterization of Mycobacterium tuberculosis isolates with low copy numbers of IS6110

Population-based analysis of Mycobacterium tuberculosis transmission in Houston, Tex., over 5 years identified 377 patients infected with an isolate containing one to four copies of IS6110. The isolates were analyzed by spoligotyping and assigned to one of three major genetic groups based on nucleotide polymorphisms in codons katG 463 and gyrA 95. Prospectively obtained patient interviews were reviewed to assess epidemiologic links between apparently clustered patients. A total of 13 groups of isolates with the same IS6110 profile were identified, representing 326 of the 377 patients (86.5%; range 2 to 113 patients). In contrast, 28 groups of isolates containing 334 patients (88.6%) had the same spoligotype (range, 2 to 143 patients). Combination of IS6110 profile and spoligotype data identified 31 clusters with 300 patients (79.6%; range, 2 to 82 patients). All 377 isolates belonged to major genetic group 1 (77 patients) or genetic group 2 (300 patients); no major genetic group 3 isolates were identified. Among the 228 patients interviewed, 33 patients (14.5%) were directly linked to another patient in the same cluster. Possible epidemiologic links were also found among 11 patients. Moreover, many clusters consisted of individuals with the same ethnicity. In conclusion, we confirmed that IS6110 profiling and spoligotyping together provide enhanced molecular discrimination of M. tuberculosis isolates with low copy numbers of IS6110. Identification of epidemiologic links among some of the patients verified that the combination of these two methods reliably indexes tuberculosis transmission.

The role of frozen section, gender, age, and tumor size in the differentiation of follicular adenoma from carcinoma: a meta-analysis

BACKGROUND

The purpose of this study was to reanalyze modern trials and use meta-analysis to determine how well frozen section gender, age, and tumor size could differentiate follicular adenoma from follicular carcinoma.

METHOD

Inclusion criteria were studies where patients had a permanent pathologic diagnosis of follicular adenoma or follicular carcinoma and underwent frozen section or had clinical features recorded. Data were pooled, and the random effects model of meta-analysis was used. A probability value of less than.05 was considered significant.

RESULTS

Nineteen studies were included (n = 3486 patients). Frozen section was evaluated in 11 studies (n = 2204 patients). Frozen section had an 87% sensitivity, a 48% specificity, a 92% and 35% positive and negative predictive value, respectively, an 82% accuracy, an odds ratio of 0.181, a 95% confidence interval (CI) of 0.07 to 0.49, and a probability value of.001. Clinical features were evaluated in 10 studies (n = 1954 patients). Of the patients with follicular carcinoma, 27.5% were male compared with patients with follicular adenoma, of whom 17.7% were male (P <.01; odds ratio, 2.17; CI 1.3-3.6; P =.003). Of the patients with follicular carcinoma, 52.2% were older than 50 years (52.2%) compared with patients with follicular adenoma, of whom 28.5% were older than 50 years (P <.001). Of patients with follicular carcinoma, 36.8% had tumors larger than 3 to 5 cm compared with patients with follicular adenoma, of whom 14.7% had tumors larger than 3 to 5 cm (P <.001; odds ratio, 3.99; CI 1.5-10.8; P =.006).

CONCLUSIONS

Meta-analysis suggests that frozen section is not a specific test and cannot be used to confidently rule out follicular carcinoma. Male gender and large tumor size are significantly associated with carcinoma.

Bacteremic and nonbacteremic pneumococcal pneumonia. A prospective study

We prospectively identified cases of pneumococcal pneumonia and used stringent criteria to stratify them into bacteremic and nonbacteremic cases. Although patients were distributed among racial groups in proportion to all patients seen at this medical center, the proportion of African-Americans with bacteremic disease was significantly increased. All patients had at least 1 underlying condition predisposing to pneumococcal infection, and most had several. Although the mean number of predisposing factors was greater among bacteremic patients than nonbacteremic patients, only alcohol ingestion was significantly more common. Nearly one-third of patients had substantial anemia (hemoglobin < or = 10 g/dL) on admission, which may have predisposed to infection. In the case of other laboratory abnormalities, such as albumin, creatinine, and bilirubin, it was difficult to determine which abnormality might have predisposed to pneumococcal infection and which might have resulted from it. The radiologic appearance was varied. Airspace consolidation and air bronchogram on chest X-ray were highly associated with bacteremic disease, as was the presence of pleural effusion. Although the Pneumonia Patient Outcomes Research Team (PORT) risk score was a predictor of mortality, it did not help to predict the presence of bacteremia in an individual case. Most patients who died in the first week in hospital were bacteremic, and a high PORT risk score with bacteremia reliably predicted a high likelihood of a fatal outcome. Eleven patients had extrapulmonary disease with meningitis, empyema, and septic arthritis predominating; all of these patients were bacteremic. The antibiotic susceptibility of our strains correlated well with those that have been reported in the United States during the years of this study. The use of numerous antibiotics of different classes in many patients, especially those who were the most ill, precluded analysis of outcome based on antibiotic therapy. Only 17 patients had been vaccinated. Since nearly all patients had conditions for which pneumococcal vaccine is recommended and more than one-third had been hospitalized in the preceding 6 months, the low rate of vaccination can be regarded as a missed opportunity to administer a potentially beneficial vaccine.

Clinical prediction model for differentiation of disseminated Histoplasma capsulatum and Mycobacterium avium complex infections in febrile patients with AIDS

BACKGROUND

Disseminated infection with Histoplasma capsulatum and Mycobacterium avium complex (MAC) in patients with AIDS are frequently difficult to distinguish clinically.

METHODS

We retrospectively compared demographic information, other opportunistic infections, medications, symptoms, physical examination findings and laboratory parameters at the time of hospital presentation for 32 patients with culture documented disseminated histoplasmosis and 58 patients with disseminated MAC infection.

RESULTS

Positive predictors of histoplasma infection by univariate analysis included lactate dehydrogenase level, white blood cell (WBC) count, platelet count, alkaline phosphatase level, and CD4 cell count. By multivariate logistic regression analysis, those characteristics that remained significant included a lactate dehydrogenase value > or =500 U/L (risk ratio [RR], 42; 95% confidence interval [CI], 18.53-97.5; p < .001), alkaline phosphatase < or =300 U/L (RR, 9.35; 95% CI, 2.61-33.48; p = .008), WBC < or =4.5 x 10(6)/L (RR, 21.29; 95% CI, 6.79-66.75; p = .008), and CD4 cell count (RR, 0.958; 95% CI, 0.946-0.971; p = .001).

CONCLUSIONS

A predictive model for distinguishing disseminated histoplasmosis from MAC infection was developed using lactate dehydrogenase and alkaline phosphatase levels as well as WBC count. This model had a sensitivity of 83%, a specificity of 91%, and a misclassification rate of 13%.

Characterization of Mycobacterium tuberculosis isolates from patients in Houston, Texas, by spoligotyping

Mycobacterium tuberculosis isolates (n = 1,429) from 1,283 patients collected as part of an ongoing population-based tuberculosis epidemiology study in Houston, Texas, were analyzed by spoligotyping and IS6110 profiling. The isolates were also assigned to one of three major genetic groups on the basis of nucleotide polymorphisms located at codons 463 and 95 in the genes (katG and gyrA) encoding catalase-peroxidase and the A subunit of DNA gyrase, respectively. A total of 225 spoligotypes were identified in the 1,429 isolates. There were 54 spoligotypes identified among 713 isolates (n = 623 patients) assigned to 73 IS6110 clusters. In addition, among 716 isolates (n = 660 patients) with unique IS6110 profiles, 200 spoligotypes were identified. No changes were observed either in the IS6110 profile or in the spoligotype for the 281 isolates collected sequentially from 133 patients. Five instances in which isolates with slightly different spoligotypes had the same IS6110 profile were identified, suggesting that in rare cases isolates with different spoligotypes can be clonally related. Spoligotypes correlated extremely well with major genetic group designations. Only three very similar spoligotypes were shared by isolates from genetic groups 2 and 3, and none was shared by group 1 and group 2 organisms or by group 1 and group 3 organisms. All organisms belonging to genetic groups 2 and 3 failed to hybridize with spacer probes 33 to 36. Taken together, the results support the existence of three distinct genetic groups of M. tuberculosis organisms and provide new information about the relationship between IS6110 profiles, spoligotypes, and major genetic groups of M. tuberculosis.

Complex transmission dynamics of clonally related virulent Mycobacterium tuberculosis associated with barhopping by predominantly human immunodeficiency virus-positive gay men

Limited data suggest that measures to reduce tuberculosis transmission should be based on locations rather than on personal contacts. Molecular epidemiologic methods (analysis of IS6110 patterns, spoligotypes, variable numbers of tandem DNA repeats, and automated DNA sequence data) identified a cohort of 48 persons who were infected with progeny of the same Mycobacterium tuberculosis strain. Epidemiologic investigation documented that a large proportion of the patients were gay white human immunodeficiency virus-positive men. Most practiced barhopping, an activity that involved patronizing many bars in the same neighborhood each night. Few subjects were directly linked to more than 1 or 2 other persons by conventional investigation methods, which shows that the transmission dynamics were unusually complex compared with most previously described episodes of strain spread. The data support the concept that identification of locations where pathogen dissemination likely occurs may provide additional strategies for targeted tuberculosis control.

Acute respiratory failure associated with cryptococcosis in patients with AIDS: analysis of predictive factors

The incidence of acute respiratory failure (ARF) associated with cryptococcal disease in patients with AIDS is underestimated in the literature. We performed a retrospective, case-control (referent) study to determine the prevalence of ARF associated with cryptococcal disease and analyzed associated factors. Potential cases of ARF were identified at four university-affiliated teaching hospitals from a cohort of 210 patients with AIDS who had positive cryptococcal antigen tests and/or Cryptococcus neoformans isolated from any body site. Twenty-nine of the 210 (13.8%) had ARF associated with cryptococcal disease. Nineteen were thought to have respiratory failure due solely to C. neoformans. The demographic, clinical, laboratory, treatment, and outcome data of 19 cases of respiratory failure were compared with data for 20 patients without respiratory failure. In-hospital mortality was 100% and median survival was 2 days for cases, vs. 25% and > 365 days, respectively, for referents. The clinical presentation was identical to that of Pneumocystis carinii pneumonia. In multivariate analysis, variables independently predictive of ARF in patients with cryptococcal disease were black race, a lactate dehydrogenase level of > or = 500 IU/L, the presence of interstitial infiltrates, and the presence of cutaneous lesions. ARF with cryptococcosis in patients with AIDS is associated with disseminated disease and high mortality. The diagnosis frequently is not considered before death. Serum cryptococcal antigen testing is a sensitive and rapid screening method.

Cryptosporidiosis in Houston, Texas. A report of 95 cases

Cryptosporidiosis is an important cause of diarrhea. We identified 95 patients with cryptosporidiosis over a 6-year period in our county hospital system, including 9 children and 86 adults infected with the human immunodeficiency virus (HIV). Risk factors included male-to-male sexual practices and Hispanic race. Diarrhea, weight loss, and gastrointestinal complaints were the most common symptoms at presentation. Among the HIV-infected adults, 20 (23%) developed biliary tract disease. Biliary involvement was associated with low CD4 counts. Treatment with paromomycin and antimotility agents was effective in reducing diarrheal symptoms in 54 of 70 (77%) patients with the acquired immunodeficiency syndrome (AIDS), although there was a high rate of relapse. Paromomycin did not prevent the development of biliary disease. Biliary disease responded to cholecystectomy or sphincterotomy with stent placement. Though often a cause of morbidity, cryptosporidiosis was only rarely the cause of death, even among patients with HIV. Cryptosporidiosis continues to be an important medical problem even in developed-countries. Current methods of prevention and treatment are suboptimal.

Genetic regulation of the capacity to make immunoglobulin G to pneumococcal capsular polysaccharides

BACKGROUND

Genetic regulation of immunoglobulin G(IgG) responses to pneumococcal capsular polysaccharides (PPS), has been demonstrated in mice but not in humans. Earlier studies from this laboratory showed that healthy adults have a varying capacity to generate IgG antibody to PPS; this study sought to determine whether this capacity is genetically controlled.

METHODS

A 23-valent pneumococcal vaccine was administered to 72 unrelated White adults, 4 nuclear families, and 61 members of an extended Ashkenazic Jewish family. Selected individuals later received one or more doses of the vaccine and/or a single dose of protein-conjugated PPS. Four to six weeks after each vaccination, IgG to PPS was measured by ELISA. Immunoglobulin allotypes and HLA types were determined by standard techniques.

RESULTS

After vaccination, 53% of the 72 unrelated White adults had measurable levels of IgG antibody to all of 10 PPS studied (high-level responders), 36% had IgG to 6-9 PPS, and 11% had IgG to < or = 5 of 10 PPS (low-level responders). Persons who did not make IgG to an individual PPS also failed to make IgM or IgA to that antigen. Low-level responders had reduced mean IgG levels to PPS to which they did make IgG; nevertheless, their total serum concentrations of IgG, IgG2, IgA, and IgM were normal, and each made IgG2 to at least one PPS, all indicating that a global defect in Ig production was not responsible. The responder status of offspring was highly associated with that of their parents. Segregation analysis of 61 Ashkenazic family members revealed that the capacity to generate anti-PPS IgG was inherited in a mixed, codominant fashion. Repeated vaccination or administration of protein-conjugated PPS did not elicit measurable IgG in nonresponders. The HLA type was not associated with antibody responses. An association between IgG level and Gm(23)+ allotype was observed in unrelated Whites but not in Ashkenazic Jews.

CONCLUSIONS

Thus, humans exhibit a variable capacity to respond to PPS. This response is hereditable in a mixed, codominant fashion. The absence of IgG to a PPS, even after antigen is presented in a protein-conjugate form, may reflect a genetically mediated failure to recognize polysaccharide antigens. Since persons who respond to fewer PPS also have lower levels of IgG to PPS to which they do respond, genetically determined deficiencies in events that involve proliferation of committed B lymphocytes may also play a role.

Molecular subtypes and antifungal susceptibilities of serial Cryptococcus neoformans isolates in human immunodeficiency virus-associated Cryptococcosis. Cryptococcal Disease Active Surveillance Group

Serial isolates of Cryptococcus neoformans from 33 human immunodeficiency virus-infected patients with cryptococcosis were analyzed to determine whether persistence might result from reinfection with a new cryptococcal strain or acquisition of antifungal resistance. Isolates were subtyped by multilocus enzyme electrophoresis (MEE), electrophoretic karyotyping (EK), random-amplified polymorphic DNA (RAPD), and the CNRE-1 DNA probe, MICs of amphotericin B, fluconazole, and 5-fluorocytosine were determined. No changes in MEE or RAPD subtypes were detected in serial isolates from any patient. Isolates from 8 patients (24%) showed alterations in EK only (mobility change in two or more bands) but not with any other subtyping method. MICs did not change significantly in isolates from 30 patients. In 1 case, the fluconazole MIC increased stepwise over 18 months, suggesting development of resistance. These overall invariant subtyping and MIC results confirm previous studies suggesting that persistent cryptococcal infection is due to relapse rather than reinfection or antifungal drug resistance.

Molecular subtype distribution of Cryptococcus neoformans in four areas of the United States. Cryptococcal Disease Active Surveillance Group

To improve understanding of the epidemiology of cryptococcal disease, we analyzed the multilocus genotype distribution of 358 Cryptococcus neoformans isolates obtained from 251 patients through active surveillance in four U.S. geographic areas from 1992 through 1994. Isolates of the predominant enzyme electrophoretic type (ET), ET-1, were recovered in significantly greater proportion from Atlanta, Ga., Houston, Tex., and all major metropolitan areas of Alabama than from San Francisco, Calif. ET-2 and ET-7 complex (serotype AD) isolates were recovered predominantly from San Francisco. ET-3 was recovered less frequently from San Francisco than from the three other locations. These findings may reflect geographic differences in exposure to environmental strains or the identification of previously unrecognized C. neoformans clusters. Analysis by random amplified polymorphic DNA-PCR subtyping further divided 67 ET-1 isolates into 19 additional subtypes, none of which could be associated with a particular geographic region. Multiple isolates from the same patient always revealed the same multilocus enzyme electrophoresis and random amplified polymorphic DNA subtypes. No differences in subtype distribution were found when isolates from AIDS patients were compared with those from persons without or with another underlying disease, although one C. noeformans var. gattii isolate was obtained from an AIDS patient. When body site distribution was analyzed, ET-4 was disproportionately recovered from skin or surface body sites. Evidence for linkage disequilibrium in this fungal population suggests that virulent C. neoformans possesses a clonal population structure. Continued application of molecular subtyping methods will be useful in tracking the source, transmission, and relative virulence of different C. neoformans strains.

The lack of association between aging and postvaccination levels of IgG antibody to capsular polysaccharides of Streptococcus pneumoniae

One possible explanation for the apparently reduced efficacy of pneumococcal vaccine in elderly subjects is that IgG responses to pneumococcal capsular polysaccharides (PPSs) decline with aging. We administered pneumococcal vaccine to 118 adults who ranged in age from 20 to 93 years; 33 were > or = 70 years old. Four to 6 weeks later, we measured IgG reactive with PPSs from 10 commonly infecting serotypes of Streptococcus pneumoniae. By regression analysis, a slight but nonsignificant increase in anti-PPS IgG was observed with increased age for six serotypes and a nonsignificant decrease was observed for four. Mean IgG levels and the percentage of subjects with IgG levels > or = 1 microgram/mL were no different among persons > or = 70 years of age than among those < or = 69 years of age. These results show no consistent effect of aging on anti-PPS IgG levels 4-6 weeks after pneumococcal vaccination.