The detection of airborne transmission of tuberculosis from HIV-infected patients, using an in vivo air sampling model

Background. Nosocomial transmission of tuberculosis remains an important public health problem. We created an in vivo air sampling model to study airborne transmission of tuberculosis from patients coinfected with human immunodeficiency virus (HIV) and to evaluate environmental control measures. Methods. An animal facility was built above a mechanically ventilated HIV‐tuberculosis ward in Lima, Peru. A mean of 92 guinea pigs were continuously exposed to all ward exhaust air for 16 months. Animals had tuberculin skin tests performed at monthly intervals, and those with positive reactions were removed for autopsy and culture for tuberculosis. Results. Over 505 consecutive days, there were 118 ward admissions by 97 patients with pulmonary tuberculosis, with a median duration of hospitalization of 11 days. All patients were infected with HIV and constituted a heterogeneous group with both new and existing diagnoses of tuberculosis. There was a wide variation in monthly rates of guinea pigs developing positive tuberculin test results (0%–53%). Of 292 animals exposed to ward air, 159 developed positive tuberculin skin test results, of which 129 had laboratory confirmation of tuberculosis. The HIV‐positive patients with pulmonary tuberculosis produced a mean of 8.2 infectious quanta per hour, compared with 1.25 for HIV‐negative patients with tuberculosis in similar studies from the 1950s. The mean monthly patient infectiousness varied greatly, from production of 0–44 infectious quanta per hour, as did the theoretical risk for a health care worker to acquire tuberculosis by breathing ward air. Conclusions. HIV‐positive patients with tuberculosis varied greatly in their infectiousness, and some were highly infectious. Use of environmental control strategies for nosocomial tuberculosis is therefore a priority, especially in areas with a high prevalence of both tuberculosis and HIV infection

Simulation of risk of tuberculosis infection in healthcare workers in hospitals of an intermediate incidence country

We simulated the frequency of tuberculosis infection in healthcare workers in order to classify the risk of TB transmission for nine hospitals in Medellín, Colombia. We used a risk assessment approach to estimate the average number of infections in three risk groups of a cohort of 1082 workers exposed to potentially infectious patients over 10- and 20-day periods. The risk level of the hospitals was classified according to TB prevalence: two of the hospitals were ranked as being of very high priority, six as high priority and one as low priority. Consistent results were obtained when the simulation was validated in two hospitals by studying 408 healthcare workers using interferon gamma release assays and tuberculin skin testing. The latent infection prevalence using laboratory tests was 41% [95% confidence interval (CI) 34·3–47·7] and 44% (95% CI 36·4–51·0) in those hospitals, and in the simulation, it was 40·7% (95% CI 32·3–49·0) and 36% (95% CI 27·9–44·0), respectively. Simulation of risk may be useful as a tool to classify local and regional hospitals according to their risk of nosocomial TB transmission, and to facilitate the design of hospital infection control plans

Working conditions and tuberculosis mortality in England and Wales, 1890-1912:a retrospective analysis of routinely collected data

BACKGROUND: Modelling studies suggest that workplaces may be important sites of Mycobacterium tuberculosis transmission in high burden countries today. Contemporary data on tuberculosis by occupation from these settings are scarce. However, historical data on tuberculosis risk in different occupations are available and may provide insight into workplace transmission. We aimed to ascertain whether, in a high burden setting, individuals working in crowded indoor environments (exposed) had greater tuberculosis mortality than individuals employed elsewhere (unexposed). METHODS: The Registrar General's Decennial Supplements from 1890-2, 1900-2 and 1910-2 contain data on mortality from tuberculosis by occupation for men in England and Wales. In these data, the association between occupational exposure to crowded indoor environments and tuberculosis mortality was assessed using an overdispersed Poisson regression model adjusting for socioeconomic position, age and decade. RESULTS: There were 23,962 deaths from tuberculosis during 14.8 million person-years of follow-up among men working in exposed occupations and 28,483 during 19.9 million person-years of follow-up among men working in unexposed occupations. We were unable to categorise a large number of occupations as exposed or unexposed. The adjusted rate ratio for death from tuberculosis was 1.34 (95 % confidence interval 1.26-1.43) comparing men working in exposed occupations to those in unexposed occupations. CONCLUSIONS: Tuberculosis mortality in England and Wales at the turn of the 20th century was associated with occupational exposure to crowded indoor environments. The association between working conditions and TB in contemporary high burden settings requires further study

Falciparum malaria in malaria-naive travellers and African visitors.

BACKGROUND: Patients from malaria-endemic areas who present in non-endemic countries with Plasmodium falciparum malaria are often assumed to have some degree of immunity. If this were reliably true, it would simplify their management. AIM: To determine whether being born and resident in a malaria-endemic country is a predictor of clinical course in UK admissions for malaria. DESIGN: Prospective observational study. METHODS: We compared clinical and laboratory parameters between two groups of adult patients with acute P. falciparum malaria, admitted to the Hospital for Tropical Diseases in London: one born and resident in non-endemic countries (n=167); the other born and resident in malaria-endemic countries of Africa (n=93). Patients were excluded if they had taken prophylaxis or prior treatment. RESULTS: There were no differences between these two groups in terms of peak parasitaemia or time to parasite clearance. There was a significantly higher risk of malaria-naive patients having peak parasitaemia >5% (OR 4.5, 95%CI 1.5-13.2). Of those usually resident in Africa, 31% required parenteral treatment compared to 41% of the malaria-naive group. Of the visitors from Africa, 4.3% needed admission to the Intensive Therapy Unit (ITU), although there was a tendency for more malaria-naive patients to require ITU care (OR 2.69, 95%CI 0.9-8.1). DISCUSSION: While there are differences in presentation between those who are malaria-naive and those who live in malaria-endemic African countries, making assumptions about the immunity or clinical course of an individual patient with malaria presenting in the UK on the basis of presumed history of exposure is unwise

Improved diagnosis of pleural tuberculosis using the microscopic- observation drug-susceptibility technique.

Tests for pleural tuberculosis are insensitive and expensive. We compared nonproprietary microscopic-observation drug-susceptibility (MODS) culture with Löwenstein-Jensen culture for evaluation of pleural specimens. MODS culture was associated with greatly increased diagnostic sensitivity and shorter time to diagnosis, compared with Löwenstein-Jensen culture (sensitivity of culture of biopsy specimens, 81% vs.51%; time to diagnosis, 11 days vs. 24 days; P < .001). The MODS technique is inexpensive, allows drug-susceptibility testing, and is a considerably improved diagnostic method for pleural tuberculosis

Movement of airborne contaminants in a hospital isolation room

We analyse the characteristics of a force-ventilated isolation room, and the contributions to transport caused by the movement of people and doors opening/closing