The Prevalence of Tuberculosis
Today, estimated two billion people – about one-third of the world population – are estimated to be infected with M. tuberculosis. The global incidence of tuberculosis (TB) peaked in 2003 and appears to be slowly declining. According to the World Health Organization (WHO), in 2013, 9 million individuals became ill with TB and 1.5 million died.
Nations with the Highest Prevalence of Tuberculosis
The highest rates (100/100,000 or higher) are observed in sub-Saharan Africa, India, and the islands of Southeast Asia and Micronesia. Intermediate rates of TB (26 to 100 cases/100,000) occur in China, Central and South America, Eastern Europe, and northern Africa. Low rates (less than 25 cases per 100,000 inhabitants) occur in the United States, Western Europe, Canada, Japan, and Australia.
Socioeconomic development and access to quality of health services appear to be at least as important as any specific TB control measure. The likelihood of success of TB control efforts is likely related to socioeconomic indicators, including gross domestic product per capita, mortality of children <5, access to clean water, and adequate sanitation and health expenditure per capita.
Tuberculosis in the United States
IN THE UNITED STATES — Following a marked decline in the incidence of tuberculosis (TB) in the United States over several decades, the incidence rose in the period 1985 to 1992. Since 1992, there has been a substantial decline in the rate of TB; in 2013, it fell to a historic low of 3.0 per 100,000. The 11.4 percent decrease between 2009 and 2008 was the greatest single year decrease ever recorded. The success in reducing the burden of TB in the United States reflects several factors including improved public health efforts, physician and patient education, infection control measures, and use of directly observed therapy.
Risk factors for tuberculosis (TB) may be divided as follows:
- Impaired immunity (host factors)
- Increased exposure to infectious persons (environmental factors)
Treatment of Tuberculosis
The primary goals of tuberculosis treatment include eradicating M. tuberculosis, preventing development of drug resistance, and preventing relapse of infection. Directly observed therapy (DOT) is the preferred strategy for treatment of all patients with tuberculosis to assure completion of appropriate therapy and prevent emergence of drug resistance. The initial phase of treatment usually consists of two months. The regimen typically consists of isoniazid, rifampin, pyrazinamide, and ethambutol. Sputum acid-fast bacilli (AFB) smears and cultures should be obtained at the time of initiation and completion of the initial phase of treatment; the latter will help identify patients at increased risk of relapse.
The continuation phase in most cases consists of isoniazid and rifampin administered for four months (six months total duration of treatment). Intermittent drug administration facilitates supervision of therapy and has been shown to be as effective as daily administration in most patients.
In general, continuous treatment is most important in the initial phase of therapy, when the organism burden is highest and the chance of developing drug resistance is greatest. The earlier in the course and the longer the duration of treatment interruption, the more serious the effect and the greater the need to restart therapy from the beginning.
Treatment of Tuberculosis and Risk of Adverse Events
The risk of adverse events is critical; therefore, baseline laboratory evaluation should include measurement of hepatic enzymes (transaminases, bilirubin, and alkaline phosphatase), complete blood count, serum creatinine, and uric acid. Testing for hepatitis B and C should be pursued for patients with epidemiologic risk factors, and counseling and testing for HIV infection should be performed on all patients. Visual acuity and red-green color discrimination testing should be obtained when treatment includes ethambutol. Furthermore, patients must be educated about the symptoms of hepatic toxicity. In general, antituberculosis agents should be discontinued if a patient’s transaminase level exceeds three times the upper limit of normal in association with symptoms or five times the upper limit of normal in the absence of symptoms. Adverse outcomes include treatment failure (positive cultures after four months of treatment) and relapse (recurrent tuberculosis at any time after completion of treatment with apparent cure).
Treatment of Tuberculosis Failure and Relapse
If relapse or treatment failure occurs, early consultation with specialty expertise should be pursued. A single drug should never be added to a failing regimen, as this may lead to acquired resistance to the new drug.
Treatment failure is defined as continuous or recurrently positive cultures during the course of appropriate antituberculous therapy. After three months of a regimen containing isoniazid (INH) and rifampin (RIF) for pulmonary tuberculosis caused by drug-susceptible organisms, 90 to 95 percent of patients have negative cultures and demonstrate clinical improvement.