Chapter 5-4: Bacterial Pneumonia

TEXTBOOK PRESENTATION

Typical onset is acute (< 1 week) with productive cough and fever. Patients may produce purulent sputum and complain of pleuritic chest pain. Presentation is similar to bacterial pneumonia in HIV-negative patients.

DISEASE HIGHLIGHTS

1. Bacterial infection is the most common cause of pneumonia associated with HIV and AIDS. HIV should therefore be considered in any patient with severe or recurrent community-­acquired pneumonia.

2. Recurrent bacterial pneumonia (> 2 episodes within 1 year) is an AIDS-defining condition.

3. May occur at any time during course of HIV infection

4. Risk of bacterial pneumonia increases as CD4TL count falls. IDU further increases the risk.

   1. CD4TL count

      1. Rate of bacterial pneumonia in HIV-negative patients: 0.9%/year

      2. Rate of bacterial pneumonia in HIV-positive patients

         1. CD4TL > 500 cells/mcL: 2.3%/year

         2. CD4TL 200–500 cells/mcL: 6.8%/year

         3. CD4TL < 200 cells/mcL: 10.8%/year

         4. Two-thirds of cases in HIV-infected patients developed in those with CD4TL < 200 cells/mcL.

   2. IDU

      1. Pneumonia incidence in HIV-infected patients who are IDUs is twice that in HIV-infected patients who are not IDUs.

      2. Increased rate of septic emboli from infective endocarditis contribute to the increased risk of pneumonia.

   3. ART significantly reduces the risk of bacterial pneumonia (45%).

5. Etiology

   1. S pneumoniae is the most common cause of bacterial pneumonia. Other common bacterial etiologies are H influenzae; Mycoplasma pneumoniae; Legionella; S aureus, including community-acquired methicillin-resistant S aureus; and Pseudomonas aeruginosa.

   2. S pneumoniae is associated with higher WBC than P aeruginosa (12,400/mcL vs 5000/mcL) and higher average CD4TL count (106 cells/mcL vs 19 cells/mcL).

   3. P aeruginosa is the reported causative pathogen in up to 38% of hospital-acquired pneumonias and 3–25% of community-acquired pneumonias; it is associated with 33% in-hospital mortality rate.

   4. Concomitant PJP is present in 13% of patients with bacterial pneumonia.

6. Complications and prognosis

   1. Bacterial pneumonia progresses more rapidly and is more often complicated in HIV-infected persons than in Non-HIV infected persons.

   2. 30% of bacterial pneumonias are associated with bacteremia; bacteremia is more common with S pneumoniae.

   3. Among hospitalized patients, overall mortality is 9.3–27%.

      1. 6–13 times higher mortality than general US population (and 1.2–2.4 times higher than population > 65 years)

      2. 5 predictors of mortality include septic shock, CD4TL count < 100 cells/mcL, significant pleural effusion (extending beyond costophrenic angle), cavities and multilobar infiltrates. Mortality is proportional to number of risk factors (Table 5-6).

      3. Mortality increases during influenza season. Influenza infection may result in either severe influenza virus pneumonia or bacterial pneumonia, most often due to S pneumoniae or S aureus.

7. Pyogenic bacterial bronchitis with productive cough, fever, and absence of infiltrates is more common in HIV-infected patients.