American Thoracic Society Journal news tips for March 2004 (first issue)

02/26/04

DOES TUBERCULOSIS RESULT FROM ONE STRAIN, OR MORE?

South African investigators have challenged the premise that tuberculosis generally results from a single strain of Mycobacterium tuberculosis by demonstrating that multiple infections are present in patients with active tuberculosis. The setting for their research was a site with a high infection rate. The researchers analyzed pre-treatment sputum specimens from 200 patients over age 15. All had been diagnosed with smear-positive TB. The authors demonstrated that 19 percent of the patients in the study were simultaneously infected with strains belonging to the Beijing and non-Beijing evolutionary lineages. The researchers said that the occurrence of multiple infections took place in 17 percent of the new tuberculosis cases. The authors also noted that from data in the study, which was collected at an epidemiologic field site in Cape Town from March 2000 to June 2002, it was not possible to predict the order in which the different infections occurred. They pointed out that reinfection might reactivate a latent infection which, in turn, might be responsible for disease progression. They said that if this scenario were true, such cases would present strains that are different from their source cases even though contact existed. The study appears in the first issue for March 2004 of the American Thoracic Society's peer-reviewed American Journal of Respiratory and Critical Care Medicine.

FIRST CULTURABLE COUGH-GENERATED TUBERCULOSIS AEROSOLS

In its initial issue for March 2004, the American Thoracic Society's peer-reviewed American Journal of Respiratory and Critical Care Medicine has published the first report of the direct isolation, quantification, and particle size determination of airborne Mycobacterium tuberculosis aerosols (capable of being cultured), which were generated from the coughs of patients with proven pulmonary tuberculosis (TB). The investigators developed a cough aerosol sampling system to test 16 subjects with smear-positive pulmonary TB. Cough-generated aerosols were positive in 4 subjects (25 percent). The authors said that there was a rapid decrease in the cough-generated aerosol cultures within the first 3 weeks of effective treatment. The culture-positive cough aerosols were associated with lack of treatment during the prior week. The studies were done in the morning before breakfast when patients were asked to provide sputa specimens for clinical purposes. All studies were performed in negative pressure isolation rooms that had six air changes per hour. No cultured M. tuberculosis was isolated from the room air. Two separate 5-minute air sampling times were chosen with the intent of maximizing aerosol collection and minimizing the discomfort of coughing. The investigators isolated 633 colony-forming units from the initial aerosol generated by one subject. After one week of treatment, the count dropped to 3 colony-forming units. This finding occurred despite the person's persistently positive smear and cultures. The authors said that their cough sampling system could be used to study the mechanics of aerosolization of the bacilli from the human respiratory tract, an area of investigation that has received relatively little attention.

DEALING WITH THE SPECIAL CLINICAL PROBLEMS OF THE MORBIDLY OBESE IN THE INTENSIVE CARE UNIT

The growing interest in gastric bypass surgery points up the problems faced by critically ill morbidly obese patients and the serious challenges seen by physicians in treating these patients. According to the American Society for Bariatric Surgery, the rate of obesity surgeries has risen from 37,000 in 2000 to 62,400 in 2001. It is expected that the total number of cases will exceed 100,000 when figures are released for 2003. This "Clinical Commentary" in the ATS journal addresses the significant differences in care for the critically ill morbidly obese patients whose mean body mass index exceeds 50. According to the author, the mechanical properties of the total respiratory system, the lung, and the chest wall of morbidly obese patients are characterized by marked derangements compared with subjects of normal weight. In a retrospective study cited, patients who were morbidly obese needed prolonged mechanical ventilation, extended ventilation weaning periods, and larger intensive care unit and hospital stays. Researchers pointed out that delayed liberation from mechanical ventilation is due to the increased work of breathing and the suboptimal lung mechanics of the patients. Morbidity from bariatric surgery can be in excess of 10 percent. Early complications include wounds splitting open, wound infection, bleeding, pulmonary embolism, and death. Compared with normal weight patients, the incidence of wound infection is significantly higher. Peritonitis from staple line leak is a serious and life-threatening complication of bariatric surgery. Proper diagnosis is often very difficult. The authors point out that the obese body is characterized by a higher proportion of tissue water and lean body mass. He explained that these alterations account for differing patterns of drug absorption and distribution that can lead to sub-therapeutic or toxic drug responses. Monitoring of serum concentrations represents the most reliable method of measuring therapeutic concentrations in the very overweight patient. The article appears in the first issue for March 2004 of the American Thoracic Society's peer-reviewed American Journal of Respiratory and Critical Care Medicine.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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