Bennett Lorber, MD
Potential Financial Conflicts of Interest: Honoraria: Merck.
Requests for Single Reprints: Bennett Lorber, MD, Section of Infectious Diseases, Temple University Hospital, Broad and Ontario Streets, Philadelphia, PA 19140; e-mail, firstname.lastname@example.org.
Lorber B.; Update in Infectious Diseases. Ann Intern Med. 2006;145:354-360. doi: 10.7326/0003-4819-145-5-200609050-00008
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Published: Ann Intern Med. 2006;145(5):354-360.
This Update in Infectious Diseases focuses on 3 main topics: emerging and reemerging infections, public health and preventive medicine, and therapeutics. In the area of emerging and reemerging infections, important papers in 2005 shed new light on disease caused by methicillin-resistant Staphylococcus aureus, respiratory syncytial virus, Clostridium difficile–associated diarrhea, and influenza. There were new findings in the area of public health and preventive medicine regarding the treatment of recurrent sexually transmitted infections and the radiographic appearance of tuberculosis. Papers in therapeutics addressed the use of intrapleural streptokinase for pleural effusion and antibiotic prophylaxis for neutropenic patients. Changes to clinical practice emerging from these articles are shown in the Table .
Julio A Leey
Senior Resident in Internal Medicine, University of Louisville
September 28, 2006
Radiographic appearance of primary TB
To the Editor: During a recent morning report at the University of Louisville Hospital, a primary tuberculosis case was presented, accompanied by discussion of a recent Update by Lorber  that highlighted an earlier article  describing predictors of the radiographic appearance of tuberculosis.
The original article was a retrospective cohort study, based on all adult patients with culture-proven pulmonary TB at Columbia University Medical Center between 1990 and 1999. Clustered cases (two or more cases with same strain by restriction fragment length polymorphism or RFLP analysis) were assumed to be due to recent transmission, indicating primary TB; unique cases (unique strains) were considered to represent reactivation of latent disease or secondary TB. Upper lobe infiltrates or cavitary lesions in the upper lobe were considered to constitute a typical film; otherwise, results were deemed atypical.
Lorber  concludes that the accepted teaching is wrong: the host immune status, not time from acquisition of infection to clinical disease, predicts the x-ray appearance of TB. We have several concerns about this conclusion, based upon the population studied and the methods used:
1. By including only adult patients with culture-proven pulmonary TB, the study's authors automatically excluded those with negative cultures, who could have had different radiographic features. Furthermore, since masking of x-ray reviewers was not reported, reading bias could have been introduced by knowing that all patients had positive cultures.
2. It is quite possible that some patients went to another hospital, making some strains falsely appear to be unique instead of being part of a cluster. Also, since around 80% of TB cases appear within 2 years of infection, some clusters may have initially resulted from reactivations, with all cases ultimately secondary to the same index case.
3. Given that New York is a very active point of migration and transit, it is possible that the index case was no longer living in New York when the reactivation cases became symptomatic, further confusing the definition of primary or secondary TB.
4. The inclusion of a population with an HIV prevalence of over 50% may itself introduce an important bias in the study. The authors imply that immunodeficiency resulting from HIV or other conditions is the most important determinant of chest radiograph appearance, but this hypothesis has not been tested in HIV-negative populations.
Additional studies on an immunocompetent population should be performed before the traditional understanding of radiographic appearance and time since infection can be rejected categorically.
Julio A. Leey, MD Senior Resident in Internal Medicine University of Louisville
W. Paul McKinney, MD Professor of Medicine University of Louisville
1.Lorber B. Update in infectious diseases. Ann Intern Med 2006;144:354-360.
2.Geng E, Kreiswirth B, Burzynski J, Schluger NW. Clinical and radiographic correlates of primary and reactivation tuberculosis: a molecular epidemiology study. JAMA 2005;293:2740-2745.
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