PPD-induced monocyte mitochondrial damage is associated with a protective effect to develop tuberculosis in BCG vaccinated individuals: A cohort study

Introduction

The mechanisms of mononuclear phagocyte death have been associated with the permissiveness and resistance to mycobacterial replication, but it remains unknown whether or not they help predict the risk of developing TB.

Objective

To describe the factors associated with the induction of monocyte mitochondrial and membrane damage in response to PPD as well as determine if this type of damage might predict the susceptibility of developing active tuberculosis in a cohort of household contacts (HHCs) from Medellin, Colombia from 2005 to 2008.

Methods

The prospective cohort study contains 2060 HHCs patients with pulmonary tuberculosis who were meticulously followed for two years. A survey of the socio-demographic, clinical, epidemiological factors and blood samples were collected. Mononuclear cell cultures were stimulated with or without PPD and the type of monocyte death was determined by the flow of cytometry, an indicator was also used for its analysis. Logistic regression was adjusted by the Generalized Estimations Equations and the survival was estimated with the Kaplan-Meier and Cox regression. Confidence intervals were used for estimating the association.

Results

1,859 out of 2,060 blood samples of the HHCs patients analyzed showed monocyte death. In response to PPD, 83.4% underwent mitochondrial damage while 50.9% had membrane damage. The membrane damage in response to PPD was higher in children under 4 years (OR: 1.57; (95% CI: 1.1 to 2.4) and the HHCs who slept regularly in the same household has an index case of (OR: 1.54; 95% CI: 1.0 to 2.3). After adjustment by age, comorbidities, nutritional status, proximity to index case and overcrowding, the risk of developing active TB among BCG vaccinated HHCs individuals with induction of mitochondrial damage was HR = 0.19 (95% CI: 0.1 to 0.5).

Conclusions

The induction of monocytes mitochondrial damage by PPD stimulation correlates with protection of TB disease development in BCG-vaccinated HHCs. This represents a potential tool to predict susceptibility of developing active disease in this population.

[Cost-effectiveness of an alternative tuberculosis treatment: home-based guardian monitoring of patients]

OBJECTIVE

Estimate the cost-effectiveness ratio of the directly observed treatment short course (DOTS) for treatment of tuberculosis (TB), comparing it to a variation of this treatment that includes increased home-based guardian monitoring of patients (DOTS-R).

METHODS

Taking a social perspective that includes the costs for the health institutions, the patients, and their family members, and for other entities that contribute to making operation of the program effective, the costs incurred with each of the two strategies were evaluated and the cost-effectiveness ratios were estimated adopting the measures of effect used by the control programs. The estimate of the cost of each of the two strategies includes the cost to the health institutions that administer treatment, the patients and their family members, and the cost to the Ministry of Health that manages public health programs on the municipal level. Based on these costs and the number of cases cured and treatments completed as outcome measures of each of the strategies evaluated, the cost-effectiveness ratio and incremental cost were calculated.

RESULTS

The DOTS-R was found to be more cost-effective for achievement of successful treatments than the DOTS. The DOTS-R recorded costs of US$ 1 122.40 to US$ 1 152.70 for each case cured compared to values of US$ 1 137.00 to US$ 1 494.30 for the DOTS. The percentage of cases treated successfully was higher with DOTS-R than with DOTS.

CONCLUSIONS

The DOTS-R is a promising cost-effective alternative for improved control of TB in endemic areas. It is recommended that the health authorities include home-based guardian monitoring of patients in their institutional management of the TB program, with the participation of health workers and the physical and financial resources that currently support this program.