Hospital outbreak of multidrug-resistant Mycobacterium tuberculosis infections. Factors in transmission to staff and HIV-infected patients

Nosocomial Tuberculosis: An Outbreak of a Strain Resistant to Seven Drugs

Objective:

To evaluate nosocomial transmission of multidrug-resistant (MDR) tuberculosis (TB).

Design:

Outbreak investigation: review of infection control practices and skin test results of healthcare workers (HCWs); medical records of hospitalized TB patients and mycobacteriology reports; submission of specimens for restriction fragment length polymorphism (RFLP) typing; and an assessment of the air-handling system.

Setting:

A teaching hospital in upstate New York.

Results:

Skin-test conversions occurred among 46 (6.6%) of 696 HCWs tested from August through October 1991. Rates were highest on two units (29% and 20%); HCWs primarily assigned to these units had a higher risk for conversion compared with HCWs tested following previous incidents of exposure to TB (relative risk [RR] = 53.4, 95% confidence interval [CI95] =6.9 to 411.1; and RR=37.4, CI95= 5.0 to 277.3, respectively). The likely source patient was the only TB patient hospitalized on both units during the probable exposure period. This patient appeared clinically infectious, was associated with a higher risk of conversion among HCWs providing direct care (RR = 2.37; CI95 = 1.05 to 5.34), and was a prison inmate with TB resistant to seven antituberculosis agents. The MDR-TB strain isolated from this patient also was isolated from other inmate and noninmate patients, and a prison correctional officer exposed in the hospital. Mycobacterium tuberculosis isolates from all of these patients had matching RFLP patterns. Infection control practices closely followed established guidelines; however, several rooms housing TB patients had marginal negative pressure with variable numbers of air changes per hour, and directional airflow was disrupted easily.

Conclusions:

These data strongly suggest nosocomial transmission of MDR-TB to HCWs, patients, and a prison correctional officer working in the hospital. Factors contributing to transmission apparently included prolonged infectiousness of the likely source patient and inadequate environmental controls. Continued urgent attention to TB infection control is needed.

SHEA-CDC TB Survey, Part I: Status of TB Infection Control Programs at Member Hospitals, 1989-1992

Objective:

To determine trends in Mycobacterium tuberculosis infection in healthcare workers, tuberculosis (TB) control measures, and compliance with the 1990 Centers for Disease Control and Prevention (CDC) guideline for preventing transmission of TB in healthcare facilities.

Design:

Voluntary questionnaire sent to all members of the Society for Healthcare Epidemiology of America, representing 359 hospitals.

Results:

Respondents’ hospitals (210 [58%]) had a median of 2,400 healthcare workers (range, 396 to 13,745), 437 beds (range, 48 to 1,250), 5.6 patients with TB per year (range, 0 to 492), and 0 multidrug-resistant (MDR) TB patients per year (range, 0 to 33). Of 166 respondents’ hospitals for which data were provided for 1989 through 1992, the number caring for MDR-TB patients increased from 10 (6%) in 1989 to 49 (30%) in 1992. Reported policies for routine healthcare worker tuberculin skin testing varied. The median skin-test positivity rate for healthcare workers at the time of hire increased from 0.54% in 1989 to 0.81% in 1992, but the median conversion rate during routine testing remained similar: 0.35% in 1989 and 0.33% in 1992. Among 196 hospitals with reported data on respiratory protection use for 1989 through 1992, the use of either surgical submicron, dust-mist, or dust-fume-mist respirators for healthcare workers increased from 9 (5%) in 1989 to 85 (43%) in 1992. Of 181 hospitals with reported data, 113 (62%) had acid-fast bacilli isolation facilities consistent with the 1990 CDC guideline (ie, a single patient room, negative air pressure relative to the hallway, air exhausted directly outside, and ≥ 6 air exchanges per hour).

Conclusions:

While the number of surveyed hospitals caring for TB and MDR-TB patients increased during 1989 through 1992, TB infection control measures at many hospitals still did not meet the 1990 CDC guideline recommendations.

Drug-resistant strains of Mycobacterium tuberculosis exhibit a range of virulence for mice

A panel of clinical isolates of Mycobacterium tuberculosis, several of which were resistant to one or more antimycobacterial drugs, were tested for their capacity to give rise to active disease following aerogenic infection of normal immunocompetent mice. The panel exhibited a range of virulence in this model, which followed no clear trend in terms of geographical source, degree of drug resistance, or rate of growth in vitro. Several isolates grew very quickly over the first 20 days in mouse lungs before being contained by emerging immunity. In view of this latter observation, we hypothesize that it is possible that such so-called fast growers may be responsible for the rapid fatality sometimes seen in immunocompromised patients with tuberculosis. Moreover, the results of the study do not support the belief that increased drug resistance usually associates with loss of virulence of the isolate.

Tuberculosis: a health education imperative returns

The ominous resurgence of tuberculosis after many years of containment necessitates a review of the various factors responsible. An intense collaborative effort is needed to avoid potentially catastrophic consequences of the new epidemic. To provide a basis for health education recommendations, the factors contributing to the resurgence of tuberculosis, the nature of the current epidemic, and past health education efforts are reviewed. Further, an expanded Health Belief Model is offered as a foundation to guide educational campaigns.

Prospective study of drug-resistant tuberculosis in a Spanish urban population including patients at risk for HIV infection

From January 1988 to October 1992, the primary resistance to first-line antituberculous drugs in 501 tuberculous patients was evaluated prospectively. Three-hundred and seventeen patients were HIV-negative and 184 were HIV-positive; these patients had several different clinical forms of tuberculosis. Moreover, the acquired resistance to antituberculous drugs was studied in 295 non-AIDS patients and in 42 AIDS patients with evidence of antecedent tuberculosis treatment. The data indicated that during these five years there was no consistent and clear-cut trend toward greater frequency of primary drug resistance to any of the first-line antituberculous drugs. Primary drug resistance in HIV-positive patients (7.1%) did not differ significantly (p > 0.05) from that found in HIV-negative patients (8.2%). Among HIV-positive patients, the acquired drug resistance pattern was similar to that detected in HIV-negative patients although the frequency of resistance in the former (69%) was significantly higher (p < 0.01). During the study, resistance to isoniazid was almost constant in the acquired-resistance cases and was frequently associated with resistance to other drugs. Furthermore, the acquired resistance to isoniazid was often of a higher level (1 to 10 mg/l) than the primary resistance (0.2 mg/l), and those strains were usually catalase and peroxidase negative.

Control of nosocomial transmission of multidrug-resistant Mycobacterium tuberculosis among healthcare workers and HIV-infected patients

From 1988 to 1990, an outbreak of multidrug-resistant tuberculosis (MDR-TB) among patients, and an increased number of tuberculin-skin-test conversions among healthcare workers, occurred on the HIV ward of Jackson Memorial Hospital, Miami, Florida, USA. Measures similar to those subsequently recommended in the 1990 Centers for Disease Control and Prevention guidelines were implemented on the HIV ward by June, 1990, and in September, 1992, we evaluated the efficacy of these control measures. Among MDR-TB patients and healthcare workers with tuberculin-skin-test conversions on the HIV ward, we looked for evidence of exposure to HIV ward MDR-TB patients positive for acid-fast bacilli in sputum during initial (January-May, 1990) and follow-up (June, 1990-June, 1992) periods. Exposure before implementation of control measures to an infectious MDR-TB patient on the HIV ward was recorded in 12 of 15 (80%) MDR-TB patients during the initial period and 5 of 11 (45%) MDR-TB patients during follow-up. After implementation of control measures, no episodes of MDR-TB could be traced to contact with infectious MDR-TB patients on the HIV ward. Skin-test conversions among workers on the HIV ward declined from 7 of 25 (28%) during the initial period to 3 of 17 (18%) in the early (June, 1990-February, 1991) and 0 of 23 in the late (March, 1991-June, 1992) follow-up periods (p < 0.01). Skin-test conversions among healthcare workers were not associated with increased exposure to MDR-TB patients, and were not significantly higher among workers on the HIV ward than on a control ward without tuberculosis patients (3/27 vs 0/16). These data demonstrate that implementation of measures similar to the Centers for Disease Control and Prevention 1990 tuberculosis-control guidelines were effective in halting transmission of MDR-TB to healthcare workers and HIV-infected patients.

Restriction fragment length polymorphism Mycobacterium tuberculosis strains isolated from Greenland during 1992: evidence of tuberculosis transmission between Greenland and Denmark

In order to describe the transmission of tuberculosis (TB) at the clonal level in a defined geographic region during a certain period of time, all isolates of Mycobacterium tuberculosis collected during 1992 from Greenland were subjected to analyses of DNA restriction fragment length polymorphism (RFLP). The RFLP patterns obtained by probing the genomic DNA with the repetitive insertion segment IS6110 revealed a high degree of similarity among the isolates, indicating a relatively high transmission rate and a close relationship between the individual M. tuberculosis clones. This was further confirmed by reprobing the Southern blots with two more-stable genetic markers, IS1081 and the DR sequence. The RFLP patterns were compared with those of 245 M. tuberculosis strains collected from Denmark during the same period (representing 91% of all new, bacteriologically verified cases of TB in Denmark in 1992). One of the three prevalent IS6110-defined clusters was traced to a group of immigrants from Greenland living in a small, defined geographical region in Denmark and to a group of Danish citizens either with known contact with these immigrants or, in other cases, with a record of previous travel or working activities in Greenland. The study showed that the present technique is extremely helpful in monitoring the spread of TB and thereby also contributing to improved disease control.

Airborne nosocomial infection: a contemporary perspective

The history of airborne nosocomial infections is reviewed, and current beliefs about such infections are placed into their historical context. Possible sources, both animate and inanimate, of airborne nosocomial infections in the hospital environment are identified. Viruses, bacteria, and fungi that have been important causes of airborne nosocomial infections in the past are discussed, and examples of key studies that have confirmed an airborne route of transmission are presented. Where relevant, measures that have been used to control airborne transmission of nosocomial pathogens are discussed. Although outbreaks of airborne nosocomial infection have been uncommon, airborne transmission appears to account for about 10% of all endemic nosocomial infections.

Use of various genetic markers in differentiation of Mycobacterium bovis strains from animals and humans and for studying epidemiology of bovine tuberculosis

One hundred fifty-three Mycobacterium bovis strains from cattle, various animal species from zoos and wild parks, and humans were analyzed for three different genetic markers for use in the epidemiology of bovine tuberculosis. M. bovis strains isolated from cattle were found to carry a single IS6110 element, whereas the majority of strains from other animals such as antelopes, monkeys, and seals harbored multiple IS6110 elements, suggesting that the reservoirs in cattle and wild animals are separated. Because the single IS6110 element in cattle strains is located at the same chromosomal position, strain differentiation by insertion sequence fingerprinting was hampered. Therefore, we investigated the usefulness of the direct repeat and polymorphic GC-rich repeat elements for strain differentiation. Both markers allowed sufficient strain discrimination for epidemiological purposes. Evidence is presented that in Argentina, most human M. bovis infections are due to transmission from cattle, whereas M. bovis infections among humans in the Netherlands are mainly contracted from animals other than cattle. Various outbreaks of M. bovis among animals and humans are described, including a small one which likely involved transmission from human to human.

Use of an insertion sequence for laboratory diagnosis and epidemiologic studies of tuberculosis

A dramatic improvement in the rapidity and accuracy of laboratory testing for tuberculosis is anticipated in the near future from the application of molecular biology techniques. The polymerase chain reaction and other nucleic acid amplification methodologies have the potential to detect, amplify, and identify very small quantities of Mycobacterium tuberculosis DNA directly in a clinical specimen, even on the same day it is collected. Within the past 3 years, a number of polymerase chain reaction-based assays for tuberculosis have emerged. The development and evaluations of the polymerase chain reaction assay based on the insertion sequence IS6110 are described. For practical application in the clinical setting, amplification assays require a simple, reliable sample preparation method; an internal positive control to monitor for inhibitors; a method for eliminating contamination with amplicon (a polymerase chain reaction product) to prevent false-positive results; and a simple, sensitive detection method. The DNA fingerprinting method that uses IS6110 probes provides a means of differentiating individual strains of M tuberculosis and is a powerful tool for epidemiologic studies. The method and its applications are described.

Surveillance of resistance to antituberculosis drugs in developing countries

Resistance to antituberculosis drugs is caused by poor management of tuberculosis control. It gives rise to treatment failure, relapse, further transmission of resistant tuberculosis, and multidrug-resistant tuberculosis. Widespread occurrence of multidrug-resistant tuberculosis would constitute a major threat to tuberculosis control in resource-poor countries. Although the impact of HIV on drug resistance is not yet fully understood, it is likely to exacerbate problems caused by drug resistance. In particular, HIV-related adverse effects of thiacetazone, together with the risks of transmission of HIV by parenteral administration of streptomycin, reduce the armamentarium available to tuberculosis control programmes in high HIV prevalence countries, and could encourage the development of resistance to the remaining drugs. While the prime need is to ensure, by good management and supervision, that resistance does not occur in the first place, surveillance of drug resistance is essential to determine the current scale and nature of the drug resistance problem, as well as to define the correct solutions.

Tuberculosis and acquired immunodeficiency syndrome: a historical perspective on recent developments

The incidence of tuberculosis has increased in recent years, at least in part as a result of the ongoing worldwide epidemic of acquired immunodeficiency syndrome (AIDS). In addition, the occurrence of outbreaks caused by multidrug-resistant Mycobacterium tuberculosis organisms has greatly heightened concern. In retrospect, a number of seminal studies that have appeared during the past decade have helped to define changing concepts concerning the epidemiology, pathogenesis, approaches to preventive care, diagnosis, and treatment of tuberculosis in HIV-infected persons. Such reports have shown that the variable clinical manifestations of tuberculosis in patients with AIDS are greatly influenced by the degree of HIV-induced immunosuppression. Explosive outbreaks of tuberculosis occurring in closed environments have emphasized that patients with AIDS and pulmonary tuberculosis may be highly contagious, especially when diagnosis and implementation of appropriate infection control measures are delayed. The extent to which homelessness and illicit drug use complicate management of tuberculosis have been examined, and the high risk of persons who are both tuberculin-positive and HIV-positive ultimately developing active tuberculosis, unless chemoprophylaxis is completed, has been clearly shown. The utility of sputum smears, bronchoscopy, and newer technologies such as polymerase chain reaction for diagnosis has been examined. The risk of relapse appears to be low when patients with AIDS with drug-sensitive tuberculosis complete appropriate multiple-drug therapy. Recent reports have addressed important hospital infection control, tuberculin testing, and chemoprophylaxis issues. This paper describes this evolution of understanding, focusing on reports that we believe have been conceptually important.

New developments in tuberculosis and HIV infection: an opportunity for prevention

As we approach 2010, the year by which we were to have eliminated TB, we find this ancient disease is making a comeback. This comeback is due to many factors, but the role of HIV infection is clearly important. HIV infection can result in changes in the pathogenesis and presentation of infection with the tubercle bacillus. Consequently, as health care providers, we must respond with changes in our usual methods of prevention, treatment, and infection control. Whereas the increase in TB is currently limited to certain geographic areas, it is likely to spread more widely. All health care providers should be aware of the changing face of TB and have a high clinical index of suspicion for this disease.

Direct detection of Mycobacterium tuberculosis complex in respiratory specimens by a target-amplified test system

A total of 938 respiratory specimens (633 sputa, 249 bronchial and tracheal aspirates, and 56 bronchoalveolar lavages) from 589 patients were tested for direct detection of Mycobacterium tuberculosis complex by the Gen-Probe amplified Mycobacterium tuberculosis direct test (MTD), and the results were compared with those of the conventional methods of fluorescence microscopy and cultivation (solid and radiometric media). One series of specimens (n = 515) was decontaminated with N-acetyl-L-cysteine (NALC)-NaOH: the other one (n = 423) was decontaminated with sodium dodecyl (lauryl) sulfate (SDS)-NaOH. Of the specimens decontaminated with NALC, 39 were MTD and culture positive, 455 were MTD and culture negative, 18 were MTD positive and culture negative, and 3 were MTD negative and culture positive, indicating a sensitivity of 92.9% and a specificity of 96.2% for the MTD. Of the specimens decontaminated with SDS, 35 were MTD and culture positive, 372 were MTD and culture negative, 15 were MTD positive and culture negative, and 1 was MTD negative and culture positive, indicating a sensitivity of 97.2% and a specificity of 96.1% for the MTD. After resolution of discrepant results by review of the patients' clinical data, the sensitivity of the MTD was 93.9%, the specificity was 97.6%, the positive predictive value was 80.7%, and the negative predictive value was 99.3% for the NALC series; the corresponding values were 97.4, 96.9, 76.0, and 99.7%, respectively, for the SDS series. In conclusion, the MTD is a highly sensitive and specific technique for detecting M. tuberculosis complex within hours in both smear-positive and smear-negative respiratory specimens.

MDR-TB. Another challenge from the microbial world

Beginning in 1985, the long decline in TB cases was dramatically reversed; from 1985 through 1992 reported cases increased 20.1 percent nationally. Two characteristics of this resurgent epidemic are unique: its prevalence among immunocompromised HIV-infected people and the emergence of multidrug-resistant TB. Current epidemiological trends, demographics and treatment approaches are discussed, as well as the implications MDR-TB holds for dentistry.

The epidemiology of multidrug-resistant tuberculosis in the United States

There has been a significant increase in the number of cases of MDR-TB in the United States. Although cases of MDR-TB have been reported from many areas of the country, the majority of the cases are concentrated in large urban areas. MDR-TB is difficult and expensive to treat. CDC has developed a National Action Plan to Combat Multidrug-Resistant Tuberculosis. The main elements of this plan include (1) greater surveillance and epidemiologic studies of drug-resistant TB; (2) initiatives to make the laboratory diagnosis of MDR-TB more rapid, sensitive, and reliable; (3) education of health care professionals about MDR-TB, its prevention, control, and treatment; and (4) measures to facilitate the development of new antituberculous drugs. CDC has published guidelines for the prevention of nosocomial spread of MDR-TB. to prevent the development and spread of MDR-TB, medical practitioners must suspect TB and make the diagnosis as rapidly as possible. Once a patient is diagnosed with TB, the most important step to prevent the development of drug-resistant disease is to ensure that patients take all of their medication. Directly observed therapy is the best way of ensuring this. In addition, more specific interventions, such as the use of incentives to improve compliance in certain situations, may need to be applied to groups in which high rates of drug resistance have been found, such as HIV-positive persons, IDUs, homeless persons, and persons who have been exposed to persons with MDR-TB. Quick and effective public health interventions targeted at these defined groups should help to control the spread of both drug-susceptible and drug-resistant TB.

The role of the public health department in tuberculosis

The role of the public health department in TB is a critical component of the overall TB control effort. This article illustrates both the traditional public health methods of surveillance, containment and prevention, and some of the newer strategies being employed to address TB control in today's multifaceted environment. It shows that controlling TB will require an intensification of collaborative efforts between public, private and community providers. In particular, the role of public health and health care workers in institutional settings is emphasized as it relates to shared community efforts. In light of the recent outbreaks of drug-resistant disease and the associated dramatic increasing TB morbidity and mortality, the need for these partnerships is urgent. Given the legal mandate for TB control, health departments will continue to play a major role in the elimination of this disease. The deterioration of these public health services, however, will require immediate attention lest the very foundation of TB control be allowed to crumble.

An overview of nosocomial infections, including the role of the microbiology laboratory

An estimated 2 million patients develop nosocomial infections in the United States annually. The increasing number of antimicrobial agent-resistant pathogens and high-risk patients in hospitals are challenges to progress in preventing and controlling these infections. While Escherichia coli and Staphylococcus aureus remain the most common pathogens isolated overall from nosocomial infections, coagulase-negative staphylococci (CoNS), organisms previously considered contaminants in most cultures, are now the predominant pathogens in bloodstream infections. The growing number of antimicrobial agent-resistant organisms is troublesome, particularly vancomycin-resistant CoNS and Enterococcus spp. and Pseudomonas aeruginosa resistant to imipenem. The active involvement and cooperation of the microbiology laboratory are important to the infection control program, particularly in surveillance and the use of laboratory services for epidemiologic purposes. Surveillance is used to identify possible infection problems, monitor infection trends, and assess the quality of care in the hospital. It requires high-quality laboratory data that are timely and easily accessible.

Enhancing infection control for elderly and medically compromised patients

Some patients may be at risk for complications from relatively common infectious diseases. Influenza, tuberculosis and methicillin-resistant Staphylococcus aureus infection can lead to illness and even death in elderly, medically compromised and institutionalized individuals. Dental personnel caring for these individuals should adopt preventive strategies that are simple and inexpensive in addition to standard infection control guidelines.

Comparison of various repetitive DNA elements as genetic markers for strain differentiation and epidemiology of Mycobacterium tuberculosis

Five different genetic elements have been found to be associated with genetic rearrangements in Mycobacterium tuberculosis complex strains. Of these elements, the insertion sequence IS6110 is presently the most frequently used genetic marker for strain differentiation of M. tuberculosis. In the present study we compared five genetic elements for their potentials to differentiate a given cluster of M. tuberculosis strains. Because of the presence of only a single copy of IS6110 or two IS6110 copies at the same chromosomal locus, a large number of strains could not be differentiated by IS6110 fingerprinting. Most strains, including the low-copy-number IS6110 strains, could be differentiated by fingerprinting with the 36-bp direct repeat or the polymorphic GC-rich repetitive DNA element. Less discriminative power was obtained with the major polymorphic tandem repeat and the insertion element IS1081. One strain which did not contain IS6110 DNA was encountered. Until now, this element has invariantly been found to be present in all M. tuberculosis complex strains. On the basis of classical taxonomic criteria and sequencing of the 16S rRNA gene, this strain was shown to be a genuine M. tuberculosis strain. Therefore, the use of this element as a target for polymerase chain reaction-facilitated detection of M. tuberculosis should be reconsidered.

Large-scale use of polymerase chain reaction for detection of Mycobacterium tuberculosis in a routine mycobacteriology laboratory

We investigated the use of DNA amplification by the polymerase chain reaction reaction (PCR) for detection of Mycobacterium tuberculosis from clinical specimens. Two-thirds of each sample was processed for smear and culture by standard methods, and one-third was submitted for DNA extraction, amplification of a 317-bp segment within the insertion element IS6110, and detection by agarose gel electrophoresis, hybridization, or both. DNA was prepared from over 5,000 samples, with 623 samples being culture positive for acid-fast bacilli. Of 218 specimens that were identified as M. tuberculosis, 181 (85%) were positive by PCR. In the M. tuberculosis culture-positive group, PCR was positive for 136 of 145 (94%) and 45 of 73 (62%) of the fluorochrome smear-positive and -negative specimens, respectively. Of 948 specimens that were either culture positive for mycobacteria other than M. tuberculosis or culture negative, 937 specimens were negative by PCR and 11 (1%) specimens initially appeared to be false positive for M. tuberculosis. The reason for discrepant results varied; some errors were traced to the presence of an inhibitor in the specimen (7.3% in unselected specimens), nucleic acid contamination, low numbers of organisms in the specimen antituberculosis therapy, and possible low-level nonspecific hybridization. In comparison with culture, the sensitivity, specificity, and positive predictive value were 83.5, 99.0, and 94.2%, respectively, for PCR. When PCR was corrected for DNA contamination, the presence of inhibitor, and culture-negative disease, the values became 86.1, 99.7, and 98.4%, respectively. If the results for multiple specimens submitted from the same patient are considered, no patient who had three of more sputum specimens tested would have been misdiagnosed.

Flexible bronchoscopy as a diagnostic tool in the evaluation of pulmonary tuberculosis in an elderly population

OBJECTIVE

This study intends to determine what role fiberoptic bronchoscopy (FOB) plays in the diagnosis of tuberculosis (TB), particularly in a geriatric population.

DESIGN

Cases of tuberculosis reported to the Tennessee Department of Health during the years 1989 and 1990 were divided into two age groups: Group A (< 65 years) and Group B (> or = 65 years). Natural sputum smears and cultures positive for M. tuberculosis (M. TB) in each group were compared with FOB specimens, acid-fast bacilli (AFB) smears and cultures. Data were analyzed by chi-square tests of independence for each year, then compared to determine statistical significance.

SETTING AND PATIENTS

Of the 601 TB cases reported to the State of Tennessee in 1989, 285 patients were in Group A and 316 in Group B. For 1990, 525 cases were reported, 269 in Group A and 256 in Group B. All cases met CDC-approved criteria for diagnosis of tuberculosis.

MEASUREMENTS

The number of positive AFB smears and M. TB cultures were compared in each group. In cases with sputum negative but FOB specimens positive for TB, identification was made by FOB only.

MAIN RESULTS

In Group A, 26 (9.1%) were diagnosed by FOB; only eight of these had positive sputum cultures. In Group B, 77 (24.4%) were diagnosed by FOB. Of these, 23 had positive sputum cultures; the remaining 54 patients (17.1%) had diagnoses based on FOB alone. In 1990, 269 cases of TB were reported in Group A. Of these, 38 (14.1%) were diagnosed by FOB. There were 256 TB cases reported among Group B, 83 (32.4%) of which were diagnosed by FOB. Of these 83 cases, 60 (23.4%) were diagnosed by FOB only. While no statistically significant difference was seen between the 1989 and 1990 rates of TB diagnosis by FOB for those in Group A (age < 65), the difference in rates for those in Group B (age > or = 65) was statistically significant (P < 0.05).

CONCLUSIONS

A steady increase in the use of FOB as a diagnostic tool was noted, suggesting that a significant number (19.9%) of geriatric TB cases might have been missed without the aid of FOB. While the exact reason for its increased utilization is not known, this study indicates that FOB has become a more important source of diagnosis in pulmonary TB, particularly among the elderly.

Mixed-linker polymerase chain reaction: a new method for rapid fingerprinting of isolates of the Mycobacterium tuberculosis complex

Rapid recognition of multidrug-resistant strains of Mycobacterium tuberculosis is a desirable goal for treatment of patients and protection of health care workers. DNA fingerprints produced with the insertion sequence IS6110 generate restriction fragment length polymorphism (RFLP) patterns that reliably identify M. tuberculosis complex strains. This report describes a rapid technique for RFLP typing using the polymerase chain reaction. The method uses one primer specific for IS6110 and a second primer complementary to a linker ligated to the restricted genomic DNA. In one strand the linker contains uracil in place of thymidine, and specific amplification is obtained by elimination of this strand with uracil N-glycosylase. Mixed-linker fingerprinting clearly differentiated multidrug-resistant isolates from 12 outbreaks and unambiguously assigned them to 26 RFLP groups.

Opportunistic pneumonia

Patients with abnormalities in their immune defense mechanisms are frequently encountered in the practice of medicine. These patients have increased susceptibility to infections that often involve the lung. Many of these infections are caused by opportunistic organisms that typically do not produce disease in individuals with a normally functioning immune system. To complicate the evaluation of these patients, they frequently develop noninfectious lung disease, which can have a radiographic appearance that is similar to infection. The purpose of this article is to present an approach to the evaluation of chest radiographic abnormalities in the immunocompromised patient with suspected pneumonia. Clinical information that is pertinent in the evaluation of immunocompromised patients is discussed. The various chest radiographic patterns seen in both infectious and noninfectious diseases that occur in the immunocompromised patient are reviewed. Integration of clinical information and radiographic findings in the development of a list of differential diagnoses is stressed.