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come of treatment in real field conditions; however, in response to the question, all patients were older than 18; 51070 were males. All patients were smear positive in both laboratories (with over 70070 3 to 4+ positive). All patients had chest roentgenograms compatible with moderate to far-advanced (old classification terminology) pulmonary tuberculosis. Our protocol guidelines recognized the likelihood that many patients might have received prior treatment and, in accord with real life conditions, patients were only excluded from the study if they admitted to having received more than 14 days of treatment within the 60-day period before beginning the proposed treatment regimen. Therefore, there is no doubt many of the patients had been previously treated; as we noted, a contemporary survey indicated a much lower prevalenceof resistance (INH 33070, streptomycin 19070) overall in the Filipino population. Hence, we concluded that the enrollment system employed - community promoters from the church - acted as a network to attract and enlist patients who had failed therapy elsewhere. To the extent that this limited the number of drug-susceptible cases in our series, it is regrettable, but the experience clearly demonstrates the need for tuberculosis treatment programs to be community wide. Moreover, this unanticipated opportunity allowed us to demonstrate in a highly quantitative manner the unfavorable impact of multi-drug resistance on the efficacy of a nominally adequate regimen. It was and should be a salient aspect of our report. ~ The decision to hospitalize the patients for one month was the choice of our collaborators in the Philippines. It was their judgment that this would expand our observations regarding tolerance/toxicity of the multi-drug regimen including administration of the thrice-weekly higher doses just prior to discharge. Also, it was their judgment that this would promote better case-holding. Certainly, as demonstrated in our recent series of patients treated in Denver with a six-month regimen, one can delete or shorten an initial hospital phase if the individual's illness does not merit inpatient care (1). We were amused that Drs. Fox and Mitchison underlined for emphasis "precisely what training the Promoters had ... ". As indicated in the article, the parish priest, upon instructions from Drs. Manalo and Tan, asked his promoters "to bring subjects with signs or symptoms of chronic pulmonary disease (cough and sputum production) to the church were sputum specimens were obtained ... "Those patients with tuberculosis proven by sputum tests were admitted to initiate therapy; upon discharge they were assigned to one single promoter who, as noted, was responsible for directly observing all subsequent medicine doses, for obtaining serial sputum specimens, and for bringing the patient in for professional observation if they became more ill (either drug toxicity or tuberculosis). These guidelines constituted the entire training of the promoters, and that explicitly is a cardinal point of our study; the community workers did not require a great deal of technical or professional instruction to perform their roles. Our simple description of potential tuberculosis patients led to a 12070 yield (207 of 1,765 sputum smears were positive for acid-fast bacilli) of individuals brought to the church. The case-holding was phenomenally high; five dropouts (3070) from the 144enrolled in the treatment, a figure rarely matched in formal trials and a tribute to the commitment and motivation of dedicated church workers. What modifications would we recommend in hindsight? Perhaps coordinating such a program with regular local health facilitieswould allow integration of more routine, newly diagnosed previously untreated, drug-susceptible cases in the community treatment program. On the other hand, this approach did help identify many patients who presumably had been living in a contagious state in the community. However, for these patients, standard regimens (even those containing rifampin) would not be sufficient. In retrospect, wewould advocate early identification of those with multi-drug resistant tuberculosis for isolation and tailored intensive chemotherapy, lest they succumb to their tuberculosis or remain as vectors for untreatable tuberculosis in generations to come. We hope that these responses help clarify our report for Drs. Fox, Mitchison, and others.

MICHAEL D. ISEMAN, M.D. Chief Clinical Mycobacteriology Service Division of Infectious Diseases National Jewish Center for Immunology and Respiratory Medicine Professor of Medicine University of Colorado School of Medicine JOHN A. SBARBARO, M.D., M.P.H. Professor of Medicine and Preventive Medicine University of Colorado School of Medicine Denver, CO 1. Cohn DL, Catlin BJ, Peterson KL, Judson FN, and Sbarbaro JA. A 62-dose, 6-month therapy for pulmonary and extrapulmonary tuberculosis. A twice-weekly, directly observed, and cost-effective regimen. Ann Intern Med 1990; 112:407-15.

MRI OF UPPER AIRWAY IN OBSTRUCTIVE SLEEP APNEA

To the Editor: With reference to the paper by Ryan and colleagues (Am Rev Respir Dis 1991; 144:939-44), we would like to bring a similar study to the attention of the authors. We studied 12 patients with obstructive sleep apnea (mean apnea-hypopnea index 48.4 ± 27.2 events/ hour) before and after a trial of nasal continuous positive airway pressure (CPAP). We were unable to show a statistically significant difference between patients' pharyngeal volumes (using a similar magnetic resonance imaging (MRI) technique) after they had used nasal CPAP nightly for 6 weeks. In addition, the patients did not show a significant improvement in their apnea-hypopnea indices after using nasal CPAP nightly when they underwent repeat sleep studies without the mask on. It is very interesting that the authors of this paper were able to find a decrease in the amount of edema and an increase in the minimal cross-sectional area. We also believed that nasal CPAP would increase the size of the pharynx by decreasing edema, and suggested in our paper that possibly our technique was not sensitive enough to detect those changes. We feel that it is much more significant, however, that the patients' 0 bstructive sleep apnea did not improve despite treatment. This suggests that even though the pharyngeal aperture may enlarge with treatment, the patient will continue to obstruct. This enforces the notion that patients with obstructive sleep apnea need to use nasal CPAP on a nightly basis. NANCY A. COLWP, M.D. Assistant Professor Medical University of South Carolina Charleston, South Carolina A. JAY

M.D., F.C.C.P. Professor University of Florida Gainesville, Florida

BWCK,

1. Collop N, Block A, Hellard D. The effect of nightly nasal CPAP treatment on underlying obstructive sleep apnea and pharyngeal size. Chest 1991; 99:855-60.

From the Authors: Wethank Drs. Collop and Block for bringing to our attention their contribution on the effect of nasal continuous positive airway pressure (CPAP) on obstructive sleep apnea (OSA) and pharyngeal size (1),which was published after the original submission of our article on magnetic resonance imaging (MRI) of the upper airway in OSA before and after chronic nasal CPAP therapy (2). In their study, they used sagittal MRI images to measure pharyngeal cross-sectional

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area before and after 6 weeks of nasal CPAP therapy and were unable to show a difference in pharyngeal size. We examined both sagittal and axial images of the upper airway in our patients. We selected the axial images for our measurements of pharyngeal crosssectional area because of the difficulty we encountered in identifying the lateral boundaries of the pharynx on the sagittal images, and the additional advantage of obtaining the site and dimensions of the minimum axial pharyngeal cross-sectional area. Using a different MRI pulse sequence and a visual grading system, we also examined upper airway mucosal water content and found that reductions in water content following chronic nasal CPAP therapy correlated with increases in pharyngeal cross-sectional area. We completely agree that regular nightly use of nasal CPAP is necessary for optimal treatment of patients with OSA, and it was never the intent of our article to suggest otherwise. We used MRI of the upper airway to advance our understanding of the pathogenesis of OSA and of the mechanisms of action of nasal CPAP therapy. C. FRANK RYAN, M.B., M.R.C.P.I., F.R.C.P.(C) JOHN A. FLEETHAM, M.D., F.R.C.P.(C) Division of Respiratory Medicine Department of Medicine University Hospital (UBC) Vancouver, B.C., Canada 1. Collop NA, Block Al, Hellard D. The effect of nightly nasal CPAP treatment on underlying obstructive sleep apnea and pharyngeal size. Chest 1991; 99:855-60. 2. Ryan CF, Lowe AA, Li D, Fleetham lA. Magnetic resonance imaging of the upper airway in obstructive sleep apnea before and after chronic nasal continuous positive airway pressure therapy. Am Rev Respir Dis 1991; 144:939-44.

STABILITY OF TUBERCULIN TESTS

To the Editor: A recent article by Gordin and colleagues (1)confirms the instability of booster responses. One year after testing, 18070 of the initially positive skin tests reverted to a negative status while 40070 of the boosted reactions reverted to negative. Gordin and associates contest that a reaction of 15 mm or greater can be used as a cutoff for considering that a followup tuberculin skin test will be positive. They note that 25070 of the boosted reactions greater than 15 mm in size were also negative after a lapse of one year. In our study (2), we concluded that true converters can be detected only with an increase of at least 12mm in the size of the reaction. This criteria implicitly accepts that some recently infected individuals with smaller increases will escape diagnosis. The tuberculin test alone is not capable of determining true conversion because of its inherent variability. The differences between our study and that of Gordin and associates are likely due to the different epidemiology of tuberculosis in Spain and the United States. In Spain the high rate of infection and reinfection is likely to lead to a lesser reversion of the skin test reaction. In addition, Gordin and coworkers studied patients under chronic care with a mean age of 69 years, whereas we performed our study on the general population with a mean age of 28 years. Fifty-one percent of the individuals in our study had been previously vaccinated with bacille Calmette-Guerin (BCG). No rigid criteria is acceptable for identifying true conversion in individuals previ-

ously vaccinated with BCG. The same statement can be applied to individuals infected with nontuberculous mycobacteria. From these arguments we believe that the paper of Gordin and colleagues does not refute our criteria used to define a true converter, especially in young individuals who would benefit from isoniazid prophylaxis. In subjects younger than 20 years of age, a number of factors, including previous BCG vaccination, contact history and the nature and size of previous tuberculin reactions, need to be considered in establishing a diagnosis of true tuberculous infection. P. DE MARCH-AYUELA, M.D. Dispensario de las Enfermedades del Torax "Dr. Luis Saye"; Barcelona, Spain 1. Gordin FM, Perez-Stable El, Reid M, Schecter G, Cosgriff L, Flaherty D, Hopewell PC. Stability of positive tuberculin tests: are boosted reactions valid? Am Rev Respir Dis 1991; 144:560-3. 2. De March-Ayuela P. Choosing an appropriate criterion for true or false conversion in serial tuberculin testing. Am Rev Respir Dis 1990; 141:815-20.

From the Authors: In response to the letter from Dr. P. de March-Ayuela, it is important to restate our methods and conclusion. In our original study (1), we applied three consecutive PPD skin tests to determine the ability of a chronic care population to demonstrate a positive reaction to a second (booster) or third skin test, all applied within 21 days as a means of identifying past infection. There was no attempt in our study to determine the conversion (or new infection) rate in our population, which we believe was misstated in table 4 of Dr. Ayuela's article on the appropriate criterion for conversion in serial tuberculin testing (2). In our most recent study (3), we commented again on the instability of boosted positive reactions and the possible clinical significance of these tests in determining past infection, without reference to conversion (or new infection) rate in our population. We agree that the definition of a tuberculin convertor as currently defined by the American Thoracic Society (4) may not accurately identify all newly infected persons. The definition of convertor as proposed by Dr. Ayuela may, in fact, be more specific. It is unfortunate that we must rely on the skin tests to identify persons infected with Mycobacterium tuberculosis; hopefully, more accurate serologic tests will be developed and put the skin test de bate "out of business." FRED M. GORDIN, M.D. Department of Veterans Affairs Medical Center Washington, D.C. PHILIP C. HOPEWELL, M.D. San Francisco General Hospital University of California, San Francisco 1. Gordin FM, Perez-Stable EF, Flaherty D, et al. Evaluation of a third sequential tuberculin skin test in a chronic care population. Am Rev Respir Dis 1988; 137:153-7. 2. De March-Ayuela P. Choosing an appropriate criterion for true or false conversion in serial tuberculin testing. Am Rev Respir Dis 1990; 141:815-20. 3. Gordin FM, Perez-Stable EF, Reid M, et al. Stability of positive tuberculin tests: are boosted reactions valid? Am Rev Respir Dis 1991; 144:560-3. 4. American Thoracic Society. The tuberculin skin test. Am Rev Respir Dis 1981; 124:356-63.