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

Obstacles encountered in application of the Centers for Disease Control and Prevention guidelines for control of tuberculosis in a large dental center

BACKGROUND

The Centers for Disease Control and Prevention (CDC) and the Occupational Safety and Health Administration have designated five categories of workplaces as carrying higher than normal risk for exposure to tuberculosis (TB); "health care facilities" is one of these categories. To assist all health care facilities in developing an appropriate and effective control plan, the CDC has listed various components to be included in the overall plan-however, the components needed cannot be determined until the level of risk has been determined. The published criteria for risk assessment are more appropriately applicable to a hospital-based facility. In complying with CDC's guidelines and adopting the recommended components of the TB control program at a large, educational, ambulatory care dental facility, several obstacles were identified.

METHODS

As part of the risk assessment for TB transmission and to determine the significance of purified protein derivative of tuberculin (PPD) skin-test conversions observed among the student and employee populations, we implemented a strategy that consisted of surveying all accredited dental schools in the country, performing a controlled PPD screening study involving predoctoral dental students in their junior year, and reviewing and evaluating all patient registration records for the same period.

RESULTS

Forty-four percent of the dental schools contacted agreed to participate in the survey. Of these, 58% had no information available on student PPD conversion rates and 29% either had no data available yet or were unwilling to share their information. Three schools (12%) that had some data and were willing to share it reported PPD conversion rates for faculty, students, or staff of 1% to 2%. The student PPD study showed a 10.7% conversion rate, but the registration record reviews showed no convincing evidence of patients with active TB having been registered at the dental school for the period of the student PPD study.

CONCLUSION

Development of a TB control program relies heavily on assessment of risk within a health care facility. The sporadic reports of PPD conversion rates among dental care workers are not adequate to determine the magnitude of exposure to TB in educational dental settings. Further studies are necessary to establish the true risk and to assist dental care facilities in developing TB control programs.

The changing face of the epidemiology of tuberculosis due to molecular strain typing--a review

About one third of the world population is infected with tubercle bacilli, causing eight million new cases of tuberculosis (TB) and three million deaths each year. After years of lack of interest in the disease, World Health Organization recently declared TB a global emergency and it is clear that there is need for more efficient national TB programs and newly defined research priorities. A more complete epidemiology of tuberculosis will lead to a better identification of index cases and to a more efficient treatment of the disease. Recently, new molecular tools became available for the identification of strains of Mycobacterium tuberculosis (M. tuberculosis), allowing a better recognition of transmission routes of defined strains. Both a standardized restriction-fragment-length-polymorphism-based methodology for epidemiological studies on a large scale and deoxyribonucleic acids (DNA) amplification-based methods that allow rapid detection of outbreaks with multidrug-resistant (MDR) strains, often characterized by high mortality rates, have been developed. This review comments on the existing methods of DNA-based recognition of M. tuberculosis strains and their peculiarities. It also summarizes literature data on the application of molecular fingerprinting for detection of outbreaks of M. tuberculosis, for identification of index cases, for study of interaction between TB and infection with the human immuno-deficiency virus, for analysis of the behavior of MDR strains, for a better understanding of risk factors for transmission of TB within communities and for population-based studies of TB transmission within and between countries.

Simultaneous detection and strain differentiation of Mycobacterium tuberculosis for diagnosis and epidemiology

Widespread use of DNA restriction fragment length polymorphism (RFLP) to differentiate strains of Mycobacterium tuberculosis to monitor the transmission of tuberculosis has been hampered by the need to culture this slow-growing organism and by the level of technical sophistication needed for RFLP typing. We have developed a simple method which allows simultaneous detection and typing of M. tuberculosis in clinical specimens and reduces the time between suspicion of the disease and typing from 1 or several months to 1 or 3 days. The method is based on polymorphism of the chromosomal DR locus, which contains a variable number of short direct repeats interspersed with nonrepetitive spacers. The method is referred to as spacer oligotyping or "spoligotyping" because it is based on strain-dependent hybridization patterns of in vitro-amplified DNA with multiple spacer oligonucleotides. Most of the clinical isolates tested showed unique hybridization patterns, whereas outbreak strains shared the same spoligotype. The types obtained from direct examination of clinical samples were identical to those obtained by using DNA from cultured M. tuberculosis. This novel preliminary study shows that the novel method may be a useful tool for rapid disclosure of linked outbreak cases in a community, in hospitals, or in other institutions and for monitoring of transmission of multidrug-resistant M. tuberculosis. Unexpectedly, spoligotyping was found to differentiate M. bovis from M. tuberculosis, a distinction which is often difficult to make by traditional methods.

Personal respiratory protection against Mycobacterium tuberculosis

Although there are no data demonstrating the effectiveness of personal respiratory protection in the prevention of occupational tuberculosis, there are sound theoretical bases supporting the use of respirators to reduce the risk of inhalational exposure. The major factor that limits the effectiveness of most respirators is the leakage between the face and the mask. There are data suggesting that traditional fit testing of respirators does not adequately predict the degree of protection in actual use, and more research is needed in that area. There is a large range of infectiousness of aerosols of TB, and classes of respirators vary greatly in the degree of protection they offer. I have argued that respirator selection should be based on anticipated exposures. High-risk exposures to TB are often associated with cough-inducing procedures or with aerosolization of infected tissues during autopsies. In my opinion, the most reasonable type of respirator for such high-risk situations in health care settings is a PAPR hood. The concentration of infectious aerosols in well-ventilated respiratory isolation rooms is likely to be very low, and the new N95 respirators offer a reasonable balance of comfort, cost, practicality, and protection. Preliminary data from mathematical modeling studies suggest there may be little additional benefit from more sophisticated personal respiratory protection in such settings. Additional research is needed to more accurately assess exposures to TB, to determine the size and aerodynamic behavior of TB generated by infectious patients, and to more accurately define the role and effectiveness of personal respiratory protection against TB.

The epidemiology of tuberculosis in the United States

After a dramatic increase in the incidence of TB in the United States from 1985 to 1992, the epidemiology of TB changed, with both the number of cases and the incidence of TB decreasing since 1992. The decreases have been focal, however, affecting only certain geographic areas (e.g., New York, California, and New Jersey) and certain populations (e.g., 25-44 year age group and people born in the United States). The factors responsible for the decrease in those areas and populations are multiple but the most important are thought to be improvements in TB control and treatment programs in communities serving populations at greatest risk for TB. Despite the overall decline in TB cases, the numbers of foreign-born people with TB continue to increase. Factors contributing to the increase in TB among foreign-born people include the prevalence of TB in the country of origin, duration of residence in the United States after immigration, inadequate screening for or treatment of TB before entering the United States, and inadequate follow-up of those who have entered the United States with noninfectious TB (i.e., abnormal chest radiograph with negative sputum smears). Control of TB among the foreign-born population is essential if the current downward trend in reported TB cases in the United States is to be maintained. The HIV epidemic had a significant impact on the increase in TB incidence in the United States in the late 1980s but improvements in measures to control transmission of TB appear to have been effective in reversing that trend. The current national decrease trend in TB morbidity can be sustained through organized efforts by federal and private agencies and state and local health departments to ensure that all people with TB are identified and treated promptly. Such efforts must be aimed at areas and populations identified as high risk for TB, especially foreign-born people and people who are infected with HIV.

Hospital infection control practices for tuberculosis

Although completely eliminating the risk for transmission of M. tuberculosis in all health-care facilities may not be possible, adherence to the principles outlined in the CDC guidelines should reduce the risk to persons in such settings. The guidelines are designed to help health-care facilities develop an infection-control plan tailored to the individual circumstances and risk in each facility. The key to maintaining an effective TB infection control plan is periodic evaluation of the plan, with reassessment of risk and revision of the plan accordingly.

Molecular epidemiology of Mycobacterium tuberculosis strains isolated from patients in a human immunodeficiency virus cohort in Switzerland

From 1989 to 1995, 46 patients infected with the human immunodeficiency virus were diagnosed with tuberculosis at the University Hospital in Zurich. Using the IS6110 insertion sequence as a genetic marker, restriction fragment length polymorphism analyses were done for 52 Mycobacterium tuberculosis isolates. We have found a large degree of IS6110 polymorphism, ranging from 1 to 16 copies. For isolates from patients from whom multiple isolates had been available, the IS6110 pattern remained virtually stable over a period of up to 4 years, as well as during emerging drug resistance. In none of the cases was a reinfection of a patient with another strain detected. For isolates from 10 patients we detected identical patterns which could be associated with four clusters. In one of these, the strains exhibited a low IS6110 copy number (four bands), and the strains were further analyzed by hybridizing with (i) the polymorphic GC-rich repetitive sequence (PGRS) and (ii) the 36-bp direct-repeat (DR) cluster sequence. One of these isolates had a different pattern with the PGRS as well as with the DR sequence and could therefore be safely excluded from that cluster. These findings point to the importance of applying more than one genetic criterion in the molecular biological study of strain relatedness.

Mycobacterial complications of HIV infection

Tuberculosis is the most common opportunistic infection worldwide and is caused by the only readily transmissible pathogen among persons with HIV infection. If treatment is initiated promptly and is supervised appropriately, cure, fortunately, is highly likely. Isoniazid preventive therapy substantially reduces the risk of tuberculosis in persons with HIV infection. Of the nontuberculous mycobacteria, Mycobacterium avium complex (MAC) is the most frequent cause of disease; however, disseminated MAC disease usually is not seen until the CD4+ cell count is less than 50 cells/L. Newer agents, such as the macrolides and rifabutin, form the nucleus of treatment regimens and also are effective in preventing the disease.

Nosocomial transmission of tuberculosis among mentally-handicapped patients in a long-term care facility

SETTING

A long-term care facility at Saint-Brieuc hospital, France.

OBJECTIVE

To investigate a nosocomial outbreak of culture-positive pulmonary tuberculosis in 6 (40%) of 15 mentally handicapped HIV-seronegative patients.

DESIGN

The factors contributing to the outbreak were analyzed and the restriction fragment length polymorphism (RFLP) patterns of the six Mycobacterium tuberculosis strains were compared.

RESULTS

RFLP analysis of the six strains demonstrated an identical banding pattern, thus confirming the spread of a unique strain. A prolonged period of contagiousness due to a delay in diagnosis of the source patient, as well as crowded living conditions in the facility, probably contributed to the outbreak. Surveillance of residents and staff in contact with the source patient resulted in the detection of five secondary cases. Because effective isolation of mentally handicapped patients in the long-term care facility turned out to be difficult, the six case-patients were transferred to the pneumology department, thus limiting the spread of tuberculosis to other residents and staff.

CONCLUSIONS

The present outbreak emphasizes the difficulties of implementing control measures for preventing the nosocomial transmission of tuberculosis in long-term care facilities for mentally handicapped patients.

Tuberculosis risk after exposure on airplanes

SETTING

Domestic and international air-flights.

OBJECTIVE

To estimate the risk of tuberculosis (TB) transmission aboard aircraft.

DESIGN

A contact investigation of passengers and crew from two flights was conducted following identification of a fellow passenger with pulmonary TB. Immediate post-exposure and follow-up tuberculin skin tests (TSTs) were obtained.

RESULTS

Of 120 contacts, 86 (72%) had a negative TST (< 5 mm); 29 (24%) a positive TST (> or = 5 mm), and 5 (4%) a TST conversion. Of the 29 persons with a positive TST, 27 had other identified risk factors for TB. Risk factors for positive TST included non-US birth (Relative Risk (RR) 9.7 P < 0.01) or history of Bacille Calmette-Guérin (BCG) vaccination (RR undefined; P < 0.01). Risk was not associated with specific aircraft or seat relative to the index case for US-born contacts. All five TST converters were born in countries where BCG vaccine is routinely given.

CONCLUSION

The positive TST reactions and conversions suggest boosting from BCG vaccination or prior exposure in TB-endemic countries. Since two positive contacts had no other identified risk factor, TB transmission on board the aircraft could not be excluded. Contact investigation of exposed aircraft passengers should be considered on a case-by-case basis, with consideration of the infectiousness of the ill passenger and the flight circumstances.

Emerging Infectious Diseases in the Institutional Setting: Another Hot Zone

During the closing years of the 20th century, there has been an unprecedented number of newly recognized infectious agents and a resurgence of infectious diseases only recently thought to be conquered. These problems have been compounded by the increasing number of pathogens that have evolved resistance to antimicrobial agents. Hospitals and other institutional settings occupy a pivotal niche in the emergence of infectious agents due to factors such as the large concentrations of ill and immunocompromised persons, evolving technologies in healthcare settings, routine breeches of host defense mechanisms, and frequent use of antimicrobial agents. Any comprehensive strategy to address emerging infectious diseases must incorporate provisions for healthcare settings, including efforts to enhance surveillance, response capacity, training, education, applied research, and routine implementation of prevention measures.

Challenges associated with assessment of risk for tuberculosis in a dental school setting

BACKGROUND

Reported risk among health care workers, related to tuberculosis exposure, motivated us to accurately assess this occupational risk at our College of Dentistry.

METHODS

Our sample population included all dental students entering their junior (third) year (beginning of maximum patient exposure). Screening for tuberculosis infection, with the standardized Mantoux test (purified protein derivative [PPD]), was conducted by the authors; several variables, previously associated with inaccurate test results in the literature, were controlled for during the study.

RESULTS

Among the study population of 158 students, the PPD conversion rate, as determined by one-step testing, after one academic year was 10.6%. To further investigate factors (other than possible workplace exposure) contributing to PPD conversion in the study population, the authors also examined PPD results from previous employee and student screenings and conducted a retrospective chart review of selected patients registered at the college for the same period.

CONCLUSIONS

We found that being born outside of the United States and having previously received bacille Calmette-Guérin vaccine are associated with positive PPD test results. In addition, PPD conversion among the study group may not be associated with occupational exposure at the College but, in fact, may be related to other factors, including community- and hospital-based clinical exposure. Finally, we recommend further research that examines the possible systemic effects of periodic testing with PPD on test subjects.

A death associated with therapy for nosocomially acquired multidrug-resistant tuberculosis

Treatment of multidrug-resistant tuberculosis is difficult and has been associated rarely with severe side effects. We report the nosocomial transmission of multidrug-resistant tuberculosis to a health-care worker who was seronegative for HIV infection. She died because of liver failure associated with treatment for active multidrug-resistant tuberculosis.

Nosocomial colonization and infection in persons infected with human immunodeficiency virus

Nosocomial infections appear to be increased in patients with acquired immunodeficiency syndrome (AIDS), compared to individuals with asymptomatic infection due to human immunodeficiency virus (HIV). Risk factors for bacterial colonization and infection include immunosuppression, prior treatment with some antibiotics, increased hospitalizations with longer lengths of stay, greater exposure to invasive devices such as indwelling intravenous or urinary catheters, and the degree of immunosuppression. Data suggest that other infectious agents such as Pneumocystis carinii, Mycobacterium tuberculosis, Mycobacterium avium complex, and Cryptosporidium may be acquired in healthcare facilities. Diagnosis and management of nosocomial infections in HIV-infected persons may be complicated by an atypical presentation, increased rates of relapse following treatment, presence of multiple infections, and early discharge from the inpatient setting. Accurate assessment of nosocomial infections and outbreaks in the hospital is complicated by limited data on the risk of transmission of both traditional and unusual pathogens in this population. Furthermore, some patients may acquire nosocomial pathogens during their initial hospitalization and present later with infections that normally would be classified as community acquired. Therefore, there probably is an underestimation of current nosocomial infection rates, and perhaps "hospital-associated" or "healthcare-facility-associated" might be more accurate terms for these infections.

Rapid diagnosis of Mycobacterium tuberculosis bacteremia by PCR

A method based on DNA amplification and hybridization has been used for the rapid detection of Mycobacterium tuberculosis in blood samples from 38 hospitalized patients (15 human immunodeficiency virus [HIV] positive and 23 HIV negative) in whom localized or disseminated forms of tuberculosis were suspected. In 32 of these patients, the diagnosis of tuberculosis was eventually confirmed by conventional bacteriological or histological procedures. M. tuberculosis DNA was detected with the PCR technique in the peripheral blood mononuclear cells from 9 of 11 (82%) HIV-infected patients and in 7 of 21 (33%) HIV-negative patients (P < 0.01), while M. tuberculosis blood cultures were positive in 1 of 8 (12.5%) and 1 of 18 (5.5%) patients, respectively. PCR was positive in all cases with disseminated disease in both HIV-negative and HIV-positive patients and also in the HIV-positive patients with extrapulmonary tuberculosis. Seven samples from patients with documented illness other than tuberculosis and 12 specimens from healthy volunteers, including seven volunteers with a recent positive purified protein derivative test, were used as controls and had a negative PCR. These results suggest that detection of M. tuberculosis DNA in peripheral blood mononuclear cells may be a useful tool for rapid diagnosis of disseminated and extrapulmonary forms of tuberculosis, especially in an HIV-positive population.

Knowledge of the Transmission of Tuberculosis and Infection Control Measures for Tuberculosis Among Healthcare Workers

Two hundred seventy-five of 325 (85%) healthcare workers (HCWs) completed a questionnaire testing their knowledge of transmission of tuberculosis (TB) and infection control measures for TB. Of the 75 HCWs with no patient contact, 49 (65%) felt that masks should be worn, and 40 (53%) would use gowns. In contrast, 175 (88%) of 200 HCWs having contact with patients thought masks should be worn, and 70 (35%) would use gowns (P=.0001 and .0085, respectively). Only 87% of HCWs with patient contact felt that respiratory precautions should be instituted for TB patients. The results of our sur vey showed that HCWs should be reeducated about TB.

Tuberculin skin testing and the health care worker: lessons of the Prophit Survey

SETTING

Concern about occupationally-acquired tuberculosis continues to grow, even as control of tuberculosis in the USA has improved. Many health care workers have developed occupationally-acquired tuberculosis in recently described outbreaks and several have died. Regulatory agencies are struggling to develop a rational policy that promises both worker safety as well as cost-effectiveness. Future infection control efforts will be evaluated by results of tuberculin skin tests of employees. However, unlike many modern diagnostic tests, the tuberculin skin test is poorly understood, may be unreliable, and requires individual physician interpretation.

DESIGN

Review of the British Prophit Survey, conducted from 1933-1944, which involved tuberculin testing of 10,000 young adults, with the goal of defining 'the relationship between tuberculin sensitivity and tuberculous immunity'.

RESULTS

Four findings are particularly pertinent to the current debate: 1. job-specific rates of tuberculin conversion and subsequent development of disease; 2. risk of exogenous re-infection among already-tuberculin positive health care workers; 3. rates of tuberculin skin test reversion; and 4. implications of induration size.

CONCLUSION

The British Prophit Survey produced a great deal of meaningful information regarding the meaning of a positive tuberculin skin test, a negative test, and a change in tuberculin status. Proper interpretation of this test requires full appreciation of its many idiosyncrasies.

Multidrug-resistant tuberculosis: prevention is better than cure

The incidence of tuberculosis, in decline in Western countries for years, is increasing again. Inadequate therapy leads to the emergence of multidrug-resistant tuberculosis, which is difficult to treat and for which there is no effective chemoprophylaxis. Prevention is the most important strategy.

Host-mediated modification of PvuII restriction in Mycobacterium tuberculosis

Restriction endonuclease PvuII plays a central role in restriction fragment length polymorphism analysis of Mycobacterium tuberculosis complex isolates with IS6110 as a genetic marker. We have investigated the basis for an apparent dichotomy in PvuII restriction fragment pattersn observed among strains of the M. tuberculosis complex. The chromosomal regions of two modified PvuII restriction sites, located upstream of the katG gene and downstream of an IS1081 insertion sequence, were studied in more detail. An identical 10-bp DNA sequence (CAGCTGGAGC) containing a PvuII site was found in both regions, and site-directed mutagenesis analysis revealed that this sequence was a target for modification. Strain-specific modification of PvuII sites was identified in DNA from over 80% of the nearly 800 isolates examined. Furthermore, the proportion of modifying and nonmodifying strains differs significantly from country to country.

Risk taking by health care workers

HEALTH CARE WORKERS (HCWs) are at risk for acquiring infections such as human immunodeficiency virus, hepatitis B virus, hepatitis C, and tuberculosis from blood and body fluids. The Centers for Disease Control established guidelines known as universal precautions (UPs) to prevent transmission of blood-borne pathogens in hospital settings, but UPs are not universally followed. CNSs are in a unique position to enhance the practice of UPs and decrease the HCW's risk-taking behavior. CNSs need to identify risk-taking behaviors and help HCWs make the right decision in risky situations. Reasons cited for noncompliance with UPs were habit, forgetfulness, influence of the nurse manager, and perceptions that barrier precautions hinder the ability to perform procedures successfully. Suggestions for improving compliance with UPs were better enforcement of guidelines, a policy mandating compliance, easy and available access to supplies, replacement of hazardous devices with safer ones, and discussion with HCWs on decision making in risky situations. CNSs possess the credibility in the clinical arena to effect change through clinical expertise, role modeling, and collaboration with HCWs.

Predominance of a single genotype of Mycobacterium tuberculosis in countries of east Asia

Analysis of the population structure of Mycobacterium tuberculosis strains from the People's Republic of China showed that the vast majority belong to a genetically closely related group. These strains shared the majority of their IS6110 DNA-containing restriction fragments, and also, the DNA polymorphism associated with other repetitive DNA elements, like the polymorphic GC-rich sequence and the direct repeat, was very limited. Because the majority of these strains originated from the province of Beijing, we designated this grouping the "Beijing family" of M. tuberculosis strains. Strains of this family were also found to dominate in neighboring countries such as Mongolia, South Korea, and Thailand, whereas a low prevalence of such strains was observed in countries on other continents. These data indicate that strains of the Beijing family recently expanded from a single ancestor which had a selective advantage. It is speculated that long-term Mycobacterium bovis BCG vaccination may be one of the selective forces implicated in the successful spread of the Beijing genotype.

Restriction fragment length polymorphism typing of Mycobacterium tuberculosis

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Hospital-acquired tuberculosis

The resurgence of tuberculosis and the emergence of drug-resistant strains, coupled with a growing number of immunocompromised patients and a high proportion of susceptible health care workers, have increased our awareness of the possibility of hospital-acquired tuberculosis. Infection control guidelines which aim to prevent dissemination and inhalation of infectious particles include early diagnosis and isolation of infectious patients, particular care during procedures likely to increase the density of the organism in the environment, and regular surveillance of hospital staff.

Mutations in katG gene sequences in isoniazid-resistant clinical isolates of Mycobacterium tuberculosis are rare

In this study, a battery of oligonucleotides was directed toward the katG gene and PCR-single-stranded conformation polymorphism (SSCP) analysis was used to search for katG gene deviations in clinical isolates of Mycobacterium tuberculosis from different geographical regions. Since a complete deletion of the katG gene was not found, it is suggested that deletion is not a major mechanism of isoniazid (isonicotinic acid hydrazide; INH) resistance in these isolates. However, 7 of 39 isolates (4 of 25 from South Africa and 3 of 14 from other geographical regions) showed mobility shifts by SSCP analysis, suggesting aberrations in the katG gene. Direct sequence analysis confirmed that the mobility shifts were due to Thr-275-->Ala (Thr275Ala), Arg409Ala, Arg463Leu, and Asp695Ala mutations and a 12-bp deletion in the 5' region of the katG gene. Mutations at codons 275, 463, and 695 created altered restriction sites for HhaI, MspI, and HaeIII, respectively, and sequence results, supported by restriction fragment length polymorphism analysis, suggested that the PCR-SSCP procedure is a good indicator of mutations in PCR-amplified fragments. Identical mutations at codons 463 and 275 were found in isolates from different geographical regions. This may suggest a common evolutionary event, but one of the control isolates (susceptible to INH [3%; n = 30]) also had a mutation at codon 463. The results suggest that variations in the katG coding gene sequences of INH-resistant isolates of M. tuberculosis are infrequent and that defects in other regions of the M. tuberculosis genome are of equal or greater importance in contributing to the acquisition of resistance to INH.

In vitro and in vivo activities of the benzoxazinorifamycin KRM-1648 against Mycobacterium tuberculosis

The in vitro and in vivo activities of a new benzoxazinorifamycin, KRM-1648 (KRM), against Mycobacterium tuberculosis were studied. The MIC at which 50% of the isolates are inhibited (MIC50) and the MIC90 of KRM for 30 fresh isolates of M. tuberculosis measured by the BACTEC 460 TB System were 0.016 and 2 micrograms/ml, respectively. These values were much lower than those for rifampin (RMP), which were 4 and >128 micrograms/ml, respectively, and considerably lower than those for rifabutin (RBT), which were 0.125 and 8 micrograms/ml, respectively. A correlational analysis of the MICs of these drugs for the clinical isolates revealed the presence of cross-resistance of the organisms to KRM and either RMP or RBT although the MICs of KRM were distributed over a much lower range than were those of the other two drugs. KRM and RMP at concentrations of 1 to 10 micrograms/ml almost completely inhibited the bacterial growth of RMP-sensitive strains (H37Rv, Kurono, and Fujii) of M. tuberculosis phagocytosed in macrophage-derived J774.1 cells. KRM was more active than RMP in inhibiting the growth of the RMP-resistant (MIC = 8 micrograms/ml) Kurata strain but failed to show such an effect against the RMP-resistant (MIC >128 micrograms/ml) Watanabe stain. When KRM was given to M. tuberculosis-infected mice at dosages of 5 to 20 mg/kg of body weight by gavage, one daily six times per week from day 1 after infection, it was much more efficacious than RMP against infections induced in mice by the RMP-sensitive Kurono strain, as measured by a reduction of rates of mortality, a reduction of the frequency and extent of gross lung lesions, histopathological changes in lung tissues, and a decrease in the bacterial loads in the lungs and spleens of infected mice. KRM also displayed significant therapeutic efficacy against infection induced by the RMP-resistant Kurata strain, while neither KRM nor RMP was efficacious against infection by the RMP-resistant Watanabe strain. In the case of infection with the Kurono strain, the efficacy of the drugs in prolonging the time of survival was in the order KRM, RBT, RMP. KRM was much more efficacious than RMP, when given at 1- to 4-week intervals. These findings suggest that KRM may be useful for the clinical treatment of tuberculosis contracted through RMP-sensitive strains, even when it is administered at long intervals.

Tuberculosis infection-control practices in United States emergency departments

STUDY OBJECTIVE

To determine the frequency with which patients with suspected tuberculosis (TB) or TB risk factors present to US emergency departments and to describe current ED TB infection-control facilities and practices.

DESIGN

Mailed survey of a sample of EDs in US acute care facilities.

PARTICIPANTS

A random sample (n = 446) of subjects who responded to a 1992 survey of all US municipal, Veterans Affairs, and university-affiliated hospitals and a 20% random sample of all private hospitals with more than 100 beds conducted by the Centers for Disease Control and Prevention (CDC).

RESULTS

We collected data on patient demographics and general ED characteristics, TB isolation facilities and policies, and employee tuberculin skin-testing policies and results. Of 446 facilities surveyed, 305 surveys (68.4%) were returned. The proportions of facilities reporting that patients suspected of having TB are seen daily, weekly, monthly, and less frequently were, respectively, 12.6%, 17.2%, 23.3%, and 46.9%. The proportion of EDs in which indigent patients are cared for on a daily basis was 89%; the homeless, 57.5%; the HIV-infected, 35.9%; i.v. drug users, 45.4%; and recent immigrants, 30%. Written criteria for isolation of patients with suspected TB at triage or in the ED were in place in 56% and 76% of facilities, respectively. TB isolation rooms fulfilling CDC guidelines were available in triage or waiting areas in 1.7% of facilities and in 19.6% of EDs. Air venting directly outside, high-efficiency particulate air filtration of recirculated air, and UV germicidal lights were used in 21%, 17%, and 8% of general patient care areas of EDs, respectively. At least one ED employee had shown tuberculin skin test conversion in 16.1% of EDs in 1991; this figure was 26.9% in 1992.

CONCLUSION

Patients with TB or at risk for TB are often treated in US EDs, and the risk for transmission of TB in this setting appears to be increasing. Prolonged waiting times and lack of infection-control facilities in EDs may contribute to this problem. Consideration should be given to implementation of policies and facilities recommended by the CDC.

Delayed recognition and infection control for tuberculosis patients in the emergency department

STUDY OBJECTIVE

The recent increase in tuberculosis (TB) cases may have an important effect on emergency department infection-control measures. We describe infection-control interventions for TB patients admitted through the ED and hypothesize that ED suspicion of TB is associated with more rapid isolation and treatment.

DESIGN

Retrospective chart review.

SETTING

The ED of a 400-bed urban, university-affiliated county hospital.

PARTICIPANTS

Fifty-five patients with TB culture-positive and acid-fast bacillus stain-positive respiratory specimens who were evaluated in the ED during 1991 and 1992.

RESULTS

We identified cases from the mycobacteriology log. Demographic and historical data and time elapsed before initiation of infection-control measures and TB therapy were recorded. We assessed the relationships of individual clinical findings and the ED presumptive diagnosis of TB (predictor variables) to time elapsed before isolation and therapy (outcome variables) with the log-rank test. The median time (interquartile range) from ED registration to isolation was 8 hours (range, 3 to 13 hours). An ED presumptive diagnosis of TB was made in 71% of cases and was significantly associated with shorter time elapsed before isolation (5 hours [range, 2 to 10 hours] versus 21 hours [range, 11 to 111 hours]; P < .001) and less time elapsed before therapy (12 hours [range, 9 to 22 hours] versus 128 hours [68 to 374 hours]; P < .001). We found TB exposure, radiographic changes typical of TB, absence of HIV risk factors, presence of cough, and sputum production to be associated with more rapid isolation.

CONCLUSION

Among patients with active pulmonary TB in the ED, TB is often unsuspected and isolation measures are often not used. ED suspicion of TB is associated with more rapid isolation and treatment.

Drug-resistant tuberculosis in pediatrics

As the incidence of tuberculosis in the United States has increased over the past 10 years, the number of cases caused by drug-resistant organisms has risen dramatically. The genetic mechanisms of resistance, which could lead to better methods of diagnosis and treatment, are being determined. Treatment of drug-resistant tuberculosis is complex, requiring the use of several toxic drugs over 9 to 18 months. At present, drug resistance is fairly localized and can be avoided in most communities if appropriate public health measures are taken. Stronger attention to treatment regimens and adherence with treatment will prevent further emergence of drug-resistant tuberculosis.

TB infection control recommendations from the CDC, 1994: considerations for dentistry. United States Centers for Disease Control and Prevention

Between 1989 and 1992, reports of outbreaks and transmissions of tuberculosis in institutional settings prompted the Centers for Disease Control and Prevention to review the guidelines for TB infection control it had published in 1990. The CDC published an updated version of the guidelines in October 1994. This article gives dentists an overview of the guidelines' recommendations that are applicable to most outpatient dental settings.

DNA fingerprinting and phenotyping of Mycobacterium tuberculosis isolates from human immunodeficiency virus (HIV)-seropositive and HIV-seronegative patients in Tanzania

With the purpose of determining whether the risk of infection with a particular clone of Mycobacterium tuberculosis is influenced by the human immunodeficiency virus (HIV) status of the host, we analyzed and compared 68 mycobacterial isolates obtained from HIV-seropositive patients with tuberculosis (TB) in Dar es Salaam, Tanzania, with 66 mycobacterial isolates obtained from HIV-seronegative patients with TB in the same geographical region by using both DNA fingerprinting and classical phenotyping methods. One hundred one different IS6110 fingerprinting patterns were observed in the 134 isolates. The level of diversity of the DNA fingerprints observed in the HIV-seropositive group was comparable to the level of the diversity observed in the HIV-seronegative group. Resistance to a single anti-TB drug was found in 8.8% of the tested isolates, and 3.2% of the isolates were resistant to more than one anti-TB drug. The drug susceptibility profiles were not significantly difference between the two groups of isolates compared in the present study. Phenotypic characteristics which classify M. tuberculosis strains as belonging to the Asian subgroup correlated with a low IS6110 copy number per isolate. However, the occurrence of Asian subgroup strains was not associated with the HIV status of the patients. The results of the study suggested an equal risk of infection with a defined M. tuberculosis clone for HIV-seropositive and HIV-seronegative individuals.

Tuberculosis in the AIDS era

A resurgence of tuberculosis has occurred in recent years in the United States and abroad. Deteriorating public health services, increasing numbers of immigrants from countries of endemicity, and coinfection with the human immunodeficiency virus (HIV) have contributed to the rise in the number of cases diagnosed in the United States. Outbreaks of resistant tuberculosis, which responds poorly to therapy, have occurred in hospitals and other settings, affecting patients and health care workers. This review covers the pathogenesis, epidemiology, clinical presentation, laboratory diagnosis, and treatment of Mycobacterium tuberculosis infection and disease. In addition, public health and hospital infection control strategies are detailed. Newer approaches to epidemiologic investigation, including use of restriction fragment length polymorphism analysis, are discussed. Detailed consideration of the interaction between HIV infection and tuberculosis is given. We also review the latest techniques in laboratory evaluation, including the radiometric culture system, DNA probes, and PCR. Current recommendations for therapy of tuberculosis, including multidrug-resistant tuberculosis, are given. Finally, the special problem of prophylaxis of persons exposed to multidrug-resistant tuberculosis is considered.

SHEA-CDC TB Survey, Part II: Efficacy of TB Infection Control Programs at Member Hospitals, 1992

Objective:

To assess the efficacy of current Myco-bacterium tuberculosis control measures.

Design:

Voluntary questionnaire to members of the Society for Healthcare Epidemiology of America.

Results:

Healthcare worker (HCW) tuberculin skin-test (TST) conversion rates were significantly higher in larger hospitals ( ≥ 437 beds) (0.9% versus 0.6%; P < 0.05), or in hospitals reporting ≥ 6 TB patients in 1992 (1.2% versus 0.6%; P < 0.05). Among larger hospitals or those hospitals surveyed reporting ≥ 6 TB patients, those without at least three of the four criteria suggested in the 1990 Centers for Disease Control and Prevention (CDC) TB guidelines for acid-fast bacilli (AFB) isolation (specifically, a single-patient room; negative pressure; and air exhausted directly outside) had significantly higher annual TST conversion rates than those with these criteria (1.8% versus 0.6%; P < 0.05). Respiratory therapist or bronchoscopist TST conversion rates were significantly lower in hospitals compliant with the exhaust criteria (1.2% versus 2.8%; P < 0.05). Regardless of hospital characteristic, HCW TST conversion rates did not differ between hospitals in which HCWs used surgical masks or used disposable particulate respirators.

Conclusion:

Among larger hospitals or hospitals reporting ≥ 6 TB patients per year, failure to comply with the 1990 CDC TB recommendations for AFB isolation room guidelines was associated with higher HCW TST conversion rates. These data suggest that complete implementation of the 1990 CDC TB guidelines would decrease HCWs’ risk of nosocomial transmission of TB in larger hospitals or those reporting more TB patients. However, in nonoutbreak situations, disposable particulate respirators or submicron surgical masks may not offer significantly greater protection to HCWs than surgical masks.