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Anatomic Alterations of the Lungs

Pneumonia, or pneumonitis with consolidation, is the result of an inflammatory process that primarily affects the gas exchange area of the lung. In response to the inflammation, fluid (serum) and some red blood cells (RBCs) from adjacent pulmonary capillaries pour into the alveoli. This process of fluid transfer is called effusion. Polymorphonuclear leukocytes move into the infected area to engulf and kill invading bacteria on the alveolar walls. This process has been termed surface phagocytosis. Increased numbers of macrophages also appear in the infected area to remove cellular and bacterial debris. If the infection is overwhelming, the alveoli become filled with fluid, RBCs, polymorphonuclear leukocytes, and macrophages. When this occurs, the lungs are said to be consolidated (Figure 15-1). Atelectasis is often associated with patients who have aspiration pneumonia.

The major pathologic or structural changes associated with pneumonia are as follows:

Etiology and Epidemidogy

Pneumonia and influenza combined are the eighth leading cause of death among all Americans and the sixth leading cause of death among all Americans over the age of 65. It is estimated that more than 60,000 Americans die of pneumonia each year. Pneumonia and influenza are especially life threatening in individuals whose lungs are already damaged by chronic obstructive pulmonary disease (COPD), asthma, or smoking. The risk of death from pneumonia or influenza is also higher among people with heart disease, diabetes, or a weakened immune system. As discussed in further detail later, causes of pneumonia include bacteria, viruses, fungi, tuberculosis, anaerobic organisms, aspiration, and the inhalation of irritating chemicals such as chlorine.

Pneumonia involving an entire lobe of the lung is called lobar pneumonia. When both lungs are involved, the condition is called double pneumonia. Although the term “walking pneumonia” has no clinical significance, it is often used to describe a mild case of pneumonia. For example, patients infected with Mycoplasma pneumoniae, who generally have mild symptoms and remain ambulatory, are sometimes told that they have “walking pneumonia”. Initially, pneumonia often mimics a common cold or the flu (e.g., the signs and symptoms develop quickly). For example, the patient suddenly experiences chills, shivering, high fever, sweating, chest pain (pleurisy), and a dry and nonproductive cough.

Pneumonia is an insidious disease because its symptoms vary greatly depending on the patient’s specific underlying condition and the type of organism causing the pneumonia. Often what is initially thought to be a cold or the flu can in fact be a much more serious pulmonary infection. The early recognition and treatment of pneumonia provide the best chance for a full recovery. There are over 30 causes of pneumonia. The major ones are listed in Box 15-1 and are discussed in the following paragraphs.

Bacterial Causes

Several types of bacteria can cause pneumonia. Bacterial pneumonia often occurs after an individual has had an upper respiratory infection such as a cold or the flu. Early signs and symptoms include shaking chills, shaking, a high fever, sweating, chest pain, an increased respiratory rate, and cough that produces yellow and green sputum. The patient may be confused or delirious. Bacterial pneumonia is often confined to just one lobe of the lung. This is called lobar pneumonia. Bacterial causes are divided into gram-positive organisms, gram-negative organisms, and anaerobic organisms. The most common are discussed in the following paragraphs.

Gram-Positive Organisms

Streptococcal pneumonia

Streptococcus pneumoniae accounts for more than 80% of all the bacterial pneumonias. The organism is a gram-positive, nonmotile coccus that is found singly, in pairs (called diplococci), and in short chains (Figure 15-2). The cocci are enclosed in a smooth, thick polysaccharide capsule that is essential for virulence. There are more than 80 different types of S. pneumoniae. Serotype 3 organisms are the most virulent. Streptococci are generally transmitted by aerosol from a cough or sneeze of an infected individual. Most strains of S. pneumoniae are sensitive to penicillin and its derivatives. S. pneumoniae also is commonly cultured from the sputum of patients having an acute exacerbation of chronic bronchitis.

Staphylococcal pneumonia

There are two major groups of Staphylococcus: (1) Staphylococcus aureus, which is responsible for most “staph” infections in humans, and (2) Staphylococcus albus and Staphylococcus epidermidis, which are part of the normal skin flora. The staphylococci are gram-positive cocci found singly, in pairs (called diplococci), and in irregular clusters (Figure 15-3). Staphylococcal pneumonia often follows a predisposing virus infection and is seen most often in children and immunosuppressed adults. S. aureus is commonly transmitted by aerosol from a cough or sneeze of an infected individual and indirectly via contact with contaminated floors, bedding, clothes, and the like. Staphylococci are a common cause of hospital-acquired pneumonia and are becoming increasingly antibiotic resistant—thus the term multiple drug–resistant S. aureus (MDRSA) organisms (some centers shorten this acronym to MRSA).

Gram-Negative Organisms

The major gram-negative organisms responsible for pneumonia are rod-shaped microorganisms called bacilli (Figure 15-4). The bacilli described in the following sections are frequently seen in the clinical setting.

Haemophilus influenzae

Haemophilus influenzae is a common inhabitant of human pharyngeal flora. H. influenzae is one of the smallest gram-negative bacilli, measuring about 1.5 mm in length and 0.3 mm in width. It appears as coccobacilli on Gram stain. There are six types of H. influenzae, designated A to F, but only type B is commonly pathogenic. Pneumonia caused by H. influenzae type B is seen most often in children aged 1 month to 6 years old. H. influenzae type B is almost always the cause of acute epiglottitis. The organism is transmitted via aerosol or contact with contaminated objects. It is sensitive to cold and does not survive long after expectoration. H. influenzae is commonly cultured from the sputum of patients having an acute exacerbation of chronic bronchitis. Additional risk factors for H. influenzae infection include COPD, defects in B-cell function, functional and anatomic asplenia, and human immunodeficiency virus (HIV) infection.

Pseudomonas aeruginosa (Bacillus Pyocyaneus)

P. aeruginosa is a highly motile, gram-negative bacillus. It colonizes the gastrointestinal tract, burns, and catheterized urinary tract and is a contaminant in many aqueous solutions. Risk factors include neutropenia, HIV infection, preexisting lung disease, endotracheal intubation, and prior antibiotic use. P. aeruginosa frequently is cultured from the respiratory tract of chronically ill, tracheostomized patients and is a leading cause of hospital-acquired pneumonia. This makes P. aeruginosa a particular problem for the respiratory care practitioner. Because the Pseudomonas organism thrives in dampness, it is frequently cultured from contaminated respiratory therapy equipment. The organism is commonly transmitted by aerosol or by direct contact with freshly contaminated articles. The sputum from patients with Pseudomonas infection is frequently green and sweet-smelling.

Atypical Organisms

Mycoplasma pneumoniae

M. pneumoniae is a common cause of mild pneumonia. These organisms cause symptoms similar to both bacterial and viral pneumonia, although the symptoms develop more gradually and are often milder. A common symptom of mycoplasma pneumonia is a cough that tends to come in violent attacks, producing only a small amount of white mucus. Chills and fever are early symptoms. Some patients experience nausea or vomiting. Some patients may experience a profound weakness that lasts for a long time.

The mycoplasma are tiny, cell wall–deficient organisms. They are smaller than bacteria but larger than viruses. The pneumonia caused by the mycoplasmal organism is described as primary atypical pneumonia—atypical because the organism escapes identification by standard bacteriologic tests. M. pneumoniae is most frequently seen in people younger than 40 years of age during the late summer and early fall months. This type of pneumonia spreads easily in areas where people congregate, such as child-care centers, schools, and homeless shelters. Patients with M. pneumoniae often are said to have “walking pneumonia” because the condition is mild (i.e., slight fever, fatigue, and a characteristic dry, hacking cough) and the patient is usually ambulatory.

Legionella pneumophila

In July 1976, a severe pneumonia-like disease outbreak occurred at an American Legion convention in Philadelphia. The causative agent eluded identification for many months, despite the concerted efforts of the nation’s top epidemiologic experts. When the organism finally was recovered from a patient, it was found to be an unusual and fastidious gram-negative bacillus with atypical concentrations of certain branched-chain lipids. The initial isolate was designated as Legionella pneumophila. More than 20 Legionella species have now been identified.

Most of the species are free-living in soil and water, where they act as decomposer organisms. The organism also multiplies in standing water such as contaminated mud puddles, large air-conditioning systems, and water tanks. The organism is transmitted when it becomes airborne and enters the patient’s lungs as an aerosol. No convincing evidence suggests that the organism is transmitted from person to person. The organism can be detected in pleural fluid, sputum, or lung tissue by direct fluorescent antibody microscopy. Although it is rarely found outside the lungs, the organism may be found in other tissues. The disease is most commonly seen in middle-aged men who smoke.

Viral Causes

Approximately half of all pneumonias are caused by viruses. More and more viruses are being identified as the cause of respiratory infections. Although most viruses attack the upper airways, some can produce pneumonia. Most of these pneumonias are not life threatening and last only a short time. Viral pneumonia tends to start with flulike signs and symptoms. The early symptoms are a dry (nonproductive) cough, headache, fever, muscle pain, and fatigue. As the disease progresses, the patient may become short of breath, cough, and produce a small amount of clear or white sputum. Viral pneumonia always carries the risk of development of a secondary bacterial pneumonia.

Viruses are minute organisms not visible by ordinary light microscopy. They are parasitic and depend on nutrients inside cells for their metabolic and reproductive needs. Approximately 90% of acute upper respiratory tract infections and 50% of lower respiratory tract infections are caused by viruses. Respiratory viruses are the most common cause of pneumonia in young children, peaking between the ages of 2 and 3. By school age, M. pneumoniae become more prevalent (see previous section). The most common viruses that cause respiratory infections are described in the following paragraphs.

Influenza Virus

Although the influenza virus has several subtypes, influenza A and B are the most common causes of viral respiratory tract infections. In the United States, influenza A and B commonly occur in epidemics during the winter months. Children, young adults, and older individuals are most at risk. Influenza is transmitted from person to person by aerosol droplets. Often the first sign of an epidemic is an increase in school absenteeism. The virus survives well in conditions of low temperatures and low humidity. It also has been found in horses, swine, and birds. Influenza viruses have an incubation period of 1 to 3 days and usually cause upper respiratory tract infections. Epidemiologists fear a pandemic of influenza, stating it is an issue of “when” and “where” rather than “if.” The recent epidemic of H1N1 (“swine flu”) is a case in point.

Respiratory Syncytial Virus

The respiratory syncytial virus (RSV) (see Chapter 36) is a member of the paramyxovirus group. Parainfluenza, mumps, and rubella

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