Microcheck 235

Pneumococcal pneumonia is typically acquired in the community and leads the list of pneumonias in adults requiring hospitalization. Pneumonia due to Klebsiella sp. and other Gram-negative rods is mainly nosocomial and leads the causes of death from nosocomial infections. Mycoplasmal pneumonia usually does not require hospitalization. Whooping cough (pertussis) is mainly a threat to infants; childhood immunization against the disease protects them, but immunity often does not persist to adulthood. Tuberculosis is a chronic disease spread from one person to another by coughing and singing. Most Mycobacterium tuberculosis infections become latent, posing the risk of reactivation throughout life. Legionella pneumophila, the bacterium that causes Legionnaires' disease, originates from waters containing other microorganisms, where it can grow within protozoa. In the human lung, the bacterium readily multiplies within macrophages.

Table 23.10 Legionnaires' Disease


Muscle aches, headache, fever, cough, shortness of breath, chest and abdominal pain, diarrhea

Incubation period

2 to 10 days

Causative agent

Legionella pneumophila, a Gram-negative bacterium that stains poorly in clinical specimens; member of the ^proteobacteria


Organism multiplies within phagocytes; released with death of the cell; necrosis of cells lining the alveoli; inflammation, and formation of microabscesses


Originates mainly from warm water contaminated with other microorganisms, such as found in air conditioning systems

Prevention and treatment

Avoidance of contaminated water aerosols; regular cleaning and disinfection of humidifying devices. Treatment: erythromycin and rifampin

Chapter 23 Respiratory System Infections

■ What feature of the S. pneumoniae cell is responsible for its virulence?

■ Why isn't pertussis toxin eliminated by the mucociliary escalator?

■ Why should people infected with M. tuberculosis react positively to a skin injection of PPD? Wouldn't a negative reaction seem more likely if the person is already infected?

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