Porth's Essentials of Pathophysiology, 4e

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Respiratory Tract Infections, Neoplasms, and Childhood Disorders

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Perfectly healthy people can be colonized and carry the organism without evidence of infection. The spread of particular strains of pneumococci, particularly anti- biotic-resistant strains, is largely by healthy, colonized individuals. The signs and symptoms of pneumococcal pneumo- nia vary widely, depending on the age and health status of the infected person. 14,26,27 In previously healthy per- sons, the onset usually is sudden and is characterized by malaise; severe, shaking chills; and fever. The tem- perature may go as high as 106°F (41°C). During the initial or congestive stage, coughing brings up watery sputum and breath sounds are limited, with fine crack- les. As the disease progresses, the character of the spu- tum changes; it may be blood tinged or rust colored to purulent. Pleuritic pain, a sharp pain that is more severe with respiratory movements, is common. With antibi- otic therapy, fever usually subsides in approximately 48 to 72 hours, and recovery is uneventful. Elderly persons are less likely to experience marked elevations in tem- perature; in these persons, the only sign of pneumonia may be a loss of appetite and deterioration in mental status. Treatment includes the use of antibiotics that are effec- tive against S. pneumoniae. In the past, S. pneumoniae was uniformly susceptible to penicillin. However, peni- cillin-resistant and multidrug-resistant strains have been emerging in the United States and other countries. The prevalence and intrinsic virulence of the pneu- mococci and their resistance to antimicrobial therapy has emphasized the need for vaccination. Two vaccine formulations are currently available: the pneumococ- cal conjugate vaccine (PCV13) and the pneumococcal polysaccharide vaccine (PPSV23). 28 The PCV13 protects against 13 types of pneumococcal bacteria. It is recom- mended for use in infants and young children and for all adults 50 years of age and older who have conditions that weaken the immune system such as HIV infection, organ transplantation, leukemia, lymphoma, and severe kidney disease. 28 The PPSV23 vaccine consists of the 23 most common capsular serotypes that cause the most common invasive pneumococcal disease. 27 It is recom- mended for all adults 65 years of age and older and for those 2 years of age and older who are at high risk for the disease. It is also recommended for adults who smoke or have asthma. 28 Legionnaires’ Disease. Legionnaires’ disease is a form of bronchopneumonia caused by a gram-negative rod, Legionella pneumophila . 14,26.29 Transmission from per- son to person has not been documented; instead, the infection typically occurs when water that contains the pathogen is aerosolized into appropriately sized drop- lets and is inhaled or aspirated by a susceptible host. Although healthy persons can contract the infection, the risk is greater among persons with chronic diseases and those with impaired cell-mediated immunity. Legionella pneumonia may present subacutely for days or a week, but more typically presents acutely with malaise, weakness, lethargy, fever, and dry cough. 29 Other manifestations include disturbances of central

nervous system function, gastrointestinal tract involve- ment, arthralgias, and elevation in body temperature, sometimes to more than 40°C (104°F). The presence of pneumonia along with diarrhea, hyponatremia, and confusion is characteristic of Legionella pneumonia. The disease causes consolidation of lung tissues and impairs gas exchange. Another characteristic of the dis- ease is a lack of a normal pulse-temperature relationship in which a fever is not accompanied by an appropri- ate rise in heart rate. 28 For example, a temperature of 102ºF is normally accompanied by a heart rate of 110 beats/min; in Legionella pneumonia it is often less than 100 beats/min. 29 Diagnosis is based on clinical manifestations, radio- logic studies, and specialized laboratory tests to detect the presence of the organism. Urine antigen tests and sputum fluorescent antibody tests allow for rapid detection of L. pneumophila serotype 1, but are less sensitive than culture for identifying other serotypes. Treatment consists of administration of antibiotics that are known to be effective against L. pneumoph- ila. Delay in instituting antibiotic therapy significantly increases mortality rates; therefore, antibiotics known to be effective against L. pneumophila should be included in the treatment regimen for severe community- acquired pneumonia. 29 Primary Atypical Pneumonia The atypical pneumonias are characterized by patchy involvement of the lung, largely confined to the alve- olar septum and pulmonary interstitium. The term atypical denotes a lack of lung consolidation, produc- tion of moderate amounts of sputum, moderate eleva- tion of white blood cell count, and lack of alveolar exudate. 14 These pneumonias are caused by a vari- ety of agents, the most common being Mycoplasma pneumoniae. Mycoplasma infections are particularly common among children and young adults. Other etiologic agents include viruses (e.g., influenza virus, respiratory syncytial virus, adenoviruses, rhinoviruses, rubella [measles] and varicella [chickenpox] viruses) and Chlamydia pneumoniae. 14 In some cases, the cause is unknown. The agents that cause atypical pneumonias damage the respiratory tract epithelium and impair respiratory tract defenses, thereby predisposing to secondary bacte- rial infections. The sporadic form of atypical pneumo- nia is usually mild with a low mortality rate. It may, however, assume epidemic proportions with intensified severity and greater mortality, as occurred in the influ- enza pandemic of 1918. The clinical course among persons with mycoplasma and viral pneumonias varies widely from a mild infec- tion that masquerades as a chest cold to a more serious and even fatal outcome. The symptoms may remain confined to fever, headache, and muscle aches and pains. Cough, when present, is characteristically dry, hacking, and nonproductive. The diagnosis is usually made based on history, physical findings, and chest radiographs.