Broadly speaking, pneumonia is an inflammation of the lung, the alveoli in particular. The different types will be covered on the Physician Assistant Exam (PANCE). It’s typically caused by an infection, with bacteria as the most popular players. Pneumonia is highly treatable, but remains a leading killer in some areas of the Third World.
Community-acquired pneumonias
Community-acquired pneumonias are classified into typical and atypical types. A typical pneumonia causes fever, chills, rigors, and the classic toxic look. An atypical pneumonia doesn’t present with the features of typical pneumonia.
The bacterial causes of CAP that you need to know for the PANCE include Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Legionella pneumophila, Chlamydophila pneumoniae, and Mycoplasma pneumoniae.
Streptococcal pneumonia
A common cause of CAP is Streptococcus pneumoniae. The usual presentation is productive cough with rust-colored sputum, fever, chills, rigors, and a toxic look. Here are the key points about streptococcal pneumonia:
Lung examination shows dry rales and increased tactile fremitus along the area.
Labs can show an elevated white count +/– a left shift or significant bandemia. Bandemia refers to production of immature neutrophils by the bone marrow. A sputum Gram stain and culture should be collected. Often, getting a good sputum sample is impossible. With streptoccocal pneumonia, the Gram stain shows the presence of Gram-positive cocci in pairs and/or chains. Hyponatremia, defined by a low serum sodium, can also be present.
A urinary pneumococcal antigen can be ordered. Even if this test is negative, it doesn’t rule out the presence of streptococcal pneumonia.
A chest radiograph may show a lobar infiltrate.
The usual initial antibiotic choices are fluoroquinolones, including levofloxacin, and a third-generation cephalosporin such as ceftriaxone plus a macrolide antibiotic such as azithromycin.
Hemophilus influenzae and Moraxella catarrhalis are two other causes of CAP. They are also two very common pathogens in patients with COPD. The antibiotic coverage is the same as in streptococcal pneumonia.
Legionnaires’ disease
Legionnaires’ disease is generally caused by Legionella pneumophila, although there are other serotypes as well. This organism is thought of as an atypical cause of CAP.
Concerning labs, a leukocytosis with bandemia may or may not be present. You can check for a urinary Legionella antigen as well. Affected patients may have nausea, vomiting, and/or diarrhea. They can also have a relative bradycardia as well. On lab tests, hyponatremia may be present.
The treatment is usually a fluoroquinolone such as levofloxacin, although the macrolide class of antibiotics can be prescribed as well.
Mycoplasma pneumonia
Like Legionnaires’, mycoplasma pneumonia is an atypical type of CAP. The bacterium Mycoplasma pneumoniae is a common etiology of pneumonia. The chest radiograph findings can be variable, although you can see opacification of certain segments of the lungs’ lower lobes. Here are a couple of points about mycoplasma pneumonia:
Getting a sputum culture for mycoplasma can be difficult if not impossible. A serologic test for cold agglutinins can be used to diagnose mycoplasma.
Mycoplasma lacks a cell wall, so you can use the macrolide class of antibiotics or the fluoroquinolones to treat this pneumonia. Tetracycline derivatives, including doxycycline, have also been used.
Chlamydial pneumonia
Chlamydophila pneumoniae is a common cause of pneumonia in kids and young people. The chest radiograph findings are similar to other atypical CAP. Because this bacterium can be difficult to isolate in sputum, you need blood antibody testing to identify the organism. Both macrolide antibiotics and tetracycline derivatives can be used to treat.
Chlamydophila psittaci is a cause of pneumonia for people who work with sick birds, usually parrots. People working in a vet’s office or pet shop are at risk. Patients can be very sick, with high fever and gastrointestinal symptoms. On physical examination, splenomegaly may be present.
Healthcare-associated pneumonias
Healthcare-associated pneumonias can affect people living in nursing homes or rehabilitation centers or people who’ve spent more than a few days in the hospital.
Gram-negative bacteria
The organisms responsible for healthcare-associated pneumonias are different from CAP organisms, tending to be more Gram-negative in scope. Examples include Pseudomonas aeruginosa and Klebsiella pneumoniae.
Treatment needs to reflect more Gram-negative coverage, including the use of third- or fourth-generation cephalosporins. Fluoroquinolones do have some Gram-negative coverage. If the person has been in the critical care unit for a while, the big Gram-negative guns can be prescribed, including the carbapenem class of beta-lactam antibiotics and monobactam aztreonam.
Staphylococcus aureus
Staph aureus pneumonia can be a superimposed bacterial infection if the person has influenza. You also find it in nursing homes, residential care facilities, and hospitals. If someone has any type of indwelling lines or catheters, he or she is at higher risk of getting a staph infection.
Classically, the pneumonia associated with Staphylococcus aureus is a cavitary pneumonia. A chest radiograph can show multiple cavitary lesions called pneumatoceles.
The treatment depends on which kind of staph infection you’re dealing with. Is it methicillin-sensitive staph aureus or methicillin-resistant staph aureus? For MSSA, penicillin antibiotics like piperacillin-tazobactam can be used. For MRSA, first-line agents can include vancomycin, although with increasing MRSA resistance, other agents like linezolid have been used.
Pneumonias in the immunocompromised patient
Many types of pneumonia can affect people who are immunocompromised. One such type of pneumonia is pneumocystis pneumonia. It’s also called pneumocystis jirovecii pneumonia and was formerly called pneumocystis carinii pneumonia. Here are the main points concerning this fungal pneumonia:
It tends to occur in immunocompromised hosts, including people with HIV whose CD4 count is < 200 and people receiving chemotherapy.
It can be a very destructive pneumonia, actually destroying the parenchyma of the lung. Serum LDH levels can be high, reflecting this destruction.
A chest radiograph can show opacification of both lung fields.
An arterial blood gas has special significance for this pneumonia. If the pO2 is < 60 mmHg, signifying hypoxemia, then steroids are given in addition to trimethoprim/sulfamethoxazole. Trimethoprim/sulfamethoxazole is often given for 21 days of therapy.