tuberculosis Flashcards
what is tuberculosis?
Tuberculosis8 (TB) is an important human disease caused by an infectious and communicable organism, Mycobac- terium tuberculosis. TB represents a major global health problem that is responsible for illness and deaths in large segments of the world’s population. The disease is spread by inhalation of infected droplets and usually demon- strates a prolonged quiescent period. M. tuberculosis replication leads to an in ammatory and granulomatous response in the host, with consequent development of classic pulmonary and systemic symptoms.
what causes tuberculosis?
In most cases of human TB, the causative agent is M. tuberculosis, an acid-fast, nonmotile, intracellular rod that is an obligate aerobe. As an aerobe, this organism exists best in an atmosphere of high oxygen tension; therefore, it most commonly infects the lung.
M. tuberculosis typically is transmitted by way of infected airborne droplets of mucus or saliva that are forcefully expelled from the lungs, most commonly through coughing but also by sneezing and during talking. The quantity and size of expelled droplets in u- ence transmission. Smaller droplets evaporate readily, leaving bacteria and other solid material as oating par- ticles that are easily inhaled. Larger droplets quickly settle to the ground. Transmission by way of fomites rarely occurs.47,55 Transmission by ingestion (e.g., of con- taminated milk) occurs but is rare because of the use of pasteurized milk. A secondary mode of transmission—by ingestion—is possible when a patient coughs up infected sputum, thereby inoculating oral tissues. Oral lesions of TB may be initiated through this mechanism.
what is the pathophysiology of tuberculosis?
TB can involve virtually any organ of the body, although the lung is the most common site of infection. The typical infection of primary pulmonary TB begins with inhala- tion of infected droplets. These droplets are carried into the alveoli, where bacteria are engulfed by macrophages.Replication occurs within alveolar macrophages, and spread of infection occurs locally to regional (hilar) lymph nodes. The combination of a primary granuloma- tous lung lesion and an infected hilar lymph node is known as a Ghon complex. If the infection is not controlled locally, distant dissemination through the bloodstream may occur. However, the vast majority of disseminated bacteria are destroyed by natural host defenses. At approximately 2 to 8 weeks after onset, delayed hypersensitivity to the bacteria develops that is mediated by T (CD4+) helper lymphocytes. This condi- tion manifests as conversion of the tuberculin skin testing (using puri ed protein derivative [PPD], as described later on) from negative to positive. Subsequently, a chronic granulomatous in ammatory reaction develops that involves activated epithelioid macrophages and formation of granulomas. These natural host defenses usually control and contain the primary pulmonary TB infection, resulting in latent tuberculosis infection (LTBI). If not contained, the nidus of infection (granuloma) may become a productive tubercle with central necrosis and caseation. Cavitation may occur (Figure 7-9), resulting in the dumping of organisms into the airway for further dissemination into other lung tissue or the exhaled air.
Limitation and local containment of infection may be influenced by a variety of factors, including host resis- tance, host immune capabilities, and virulence of the mycobacterium. Once the infection has been successfully interrupted, the lesion heals spontaneously and then undergoes inspissation, hardening, encapsulation, and calci cation. Although the lesion “heals,” some bacteria may remain dormant. If infection is not interrupted, dissemination of bacilli may occur through the lung parenchyma, resulting in extensive pulmonary lesions and lymphohematogenous spread. Widespread infection with multiple organ involvement is called miliary tuberculosis.
what’s the difference between primary and secondary tuberculosis?
Primary pulmonary TB is seen most often in infants and children; however, cavitation is rare in these age groups, and children generally do not actively produce or expectorate sputum; they instead usually swallow any pulmonary secretions. Expression of the disease differs somewhat in teenagers and adults in that lymph node involvement and lymphohematogenous spread are not prominent features. However, cavitation commonly occurs. The usual form of disease found in adults is called secondary or reinfection TB, which occurs with delayed reactivation of persistent dormant viable bacilli and probably represents relapse of a previous infection. This form of the disease usually is con ned to the lungs, and cavitation is common. Reasons for relapse include inadequate treatment of the primary infection and the in uences of illness, immunosuppressive agents, immu- node ciency disease (as in AIDS), and age.
who are the persons at increased risk for progression of infection to active tuberculosis?
Persons with human immunode ciency virus infection
• Infants and children younger than 5 years of age
• Persons who are receiving immunosuppressive therapy such as
with tumor necrosis factor-α (TNF-α) antagonists, or systemic corticosteroids equivalent to 15 mg or more of prednisone per day, or immunosuppressive drug therapy after organ transplantation
• Persons who were recently infected with M. tuberculosis (within the past 2 years)
• Persons with a history of untreated or inadequately treated active tuberculosis, including persons with brotic changes on chest radiograph consistent with previous active tuberculosis
• Persons with silicosis, diabetes mellitus, chronic renal failure, leukemia, lymphoma, solid organ transplant, or cancer of the head, neck, or lung
• Persons who have had a gastrectomy or jejunoileal bypass
• Persons who are underweight (weigh less than 90% of their
ideal body weight) or malnourished
• Cigarette smokers and persons who abuse drugs or alcohol
• Populations de ned locally as having an increased incidence of
active tuberculosis, possibly including medically underserved or low-income populations
When is it safe to treat a patient on TB medications?
· Main concern of treating those with TB is spread of infection
· Tx for those who have been recently diagnosed, have clinically active TB and positive sputum cultures should not be treated on an outpatient bases
o Best done in a hospital setting with appropriate isolation, sterilization, engineered control (e.g. ventilation) systems and filtered masks
o Tx should be limited to urgent dental care
o A rubber dam should be used to minimize aerosolization of oropharyngeal microbes
· Tx can be given to outpatients when:
o They’ve taken chemotherapy for 2 to 3 weeks and after receiving confirmation from the physician the he or she is noninfectious and lacks any complicating factors
o Guidelines for determining when a patient with TB is noninfectious during therapy include:
§ Likelihood of multidrug-resistant TB has been determined to be negligible
§ Pt has received standard multidrug anti-TB therapy for 2 to 3 weeks
§ Patient has demonstrated compliance with standard multidrug anti-TB treatment
§ Patient exhibits clinical improvement
§ Results of AFB testing on three consecutive sputum smears are negative
§ All close contacts of the patient have been identified, evaluated, advised, and, if indicated, started on trx for latent TB infection
o Pt is then treated as normal
o Children with active TB but who are receiving chemotherapy usually can be treated as an outpatient (
