What is the most common type of pneumonia following influenza (flu)?

From the Guidelines

The most common pneumonia following influenza is caused by Streptococcus pneumoniae, though Staphylococcus aureus is also a common cause, particularly in severe cases. This typically occurs as a secondary bacterial infection after the flu virus damages respiratory epithelium, impairs mucociliary clearance, and alters immune responses, creating an environment conducive to bacterial invasion 1. According to the American Thoracic Society and Infectious Diseases Society of America guidelines, bacterial pneumonia can occur concurrently with influenza virus infection or present later as a worsening of symptoms in patients who were recovering from their primary influenza virus infection 1.

Key points to consider in the management of post-influenza pneumonia include:

• The use of standard antibacterial treatment for adults with clinical and radiographic evidence of community-acquired pneumonia (CAP) who test positive for influenza 1
• The selection of appropriate antibiotic agents, such as amoxicillin, levofloxacin, or ceftriaxone, depending on the severity of the pneumonia and the suspected or confirmed pathogen 1
• The importance of monitoring for clinical stability and adjusting antibiotic therapy as needed to minimize the risk of treatment failure and complications 1
• The potential for shorter courses of antibiotic therapy, typically 5-7 days, in patients with CAP, including those with post-influenza pneumonia 1

It is essential to note that prevention strategies, such as annual influenza vaccination and pneumococcal vaccination for eligible individuals, can significantly reduce the risk of both primary viral infection and subsequent bacterial pneumonia complications 1. Patients should seek medical attention promptly if experiencing worsening symptoms after initial flu improvement, particularly persistent fever, increased shortness of breath, or productive cough with purulent sputum.

From the Research

Most Common Pneumonia Post Flu

• Streptococcus pneumoniae is one of the most common causes of bacterial community-acquired pneumonia (CAP) 2
• The pneumococcus is associated with a significant burden of disease, causing substantial morbidity and mortality worldwide, and generating considerable health-care costs 2
• Risk factors for pneumococcal infection include extremes of age, lifestyle factors, and various underlying comorbid conditions, including congenital and acquired immunodeficiencies 2

Treatment of Pneumococcal Pneumonia

• Beta-lactam antibiotics, such as penicillin G, amoxicillin, amoxicillin-clavulanate, cefuroxime, cefotaxime, or ceftriaxone, are recommended for the treatment of nonmeningeal pneumococcal infections 3
• Amoxicillin-clavulanate and ceftriaxone are equally safe and effective for the empirical treatment of acute bacterial pneumonia, including penicillin and cephalosporin-resistant pneumococcal pneumonia 4
• The use of appropriate beta-lactams in patients with pneumococcal pneumonia and in the overall CAP population is reliable at the current level of resistance 4

Antibiotic Resistance

• The incidence of penicillin resistance in strains of S. pneumoniae approaches 40% in some areas of the United States, and the incidence of high-level resistance has increased by 60-fold during the past 10 years 3
• The mechanism of beta-lactam resistance of S. pneumoniae involves genetic mutations which alter penicillin-binding protein structure, resulting in a decreased affinity for all beta-lactam antibiotics 3
• Antibiotic therapy does not directly increase the number of resistant strains in the population but, by eradicating susceptible strains, allows greater opportunity for carriage and spread of resistant strains 5