Secondary bacterial pneumonia in flu

Tuesday 18th August 2009:HCFI New Delhi:  Secondary bacterial pneumonia is an important complication of flu and contributes to about 25 percent of all flu -associated deaths said   Dr KK Aggarwal President, Heart Care Foundation of India, BSNL Dil Ka Darbar, MTNL Perfect Health Mela and Director, IMA AKN Sinha Institute.

The hallmark of the clinical presentation in patients with secondary bacterial pneumonia is the exacerbation of fever and respiratory symptoms after initial improvement in the symptoms of acute flu. Fever may abate for one day or more after two to three days of acute flu, but, instead of continuing to improve, the patient with secondary bacterial pneumonia relapses with higher fevers, cough, production of purulent sputum, and x ray evidence of pulmonary infiltrates.

Flu virus affects tracheobronchial epithelium, directly leading to a decrease in the size of the cells and loss of cilia. These events may predispose to bacterial infection of the lung (secondary bacterial pneumonia) and increased mortality.

The most common bacterial pathogen is Streptococcus pneumoniae (48 percent of cases). Staphylococcus aureus, which is an unusual cause of community-acquired pneumonia, is the second most common organism (19 percent), and Haemophilus influenzae pneumonia also may complicate influenza. Community-associated methicillin-resistant Staphylococcus aureus has been identified in outbreaks of severe pneumonia with a high mortality rate in patients with influenza.

Primary influenza pneumonia — Primary influenza pneumonia occurs when influenza virus infection directly involves the lung, typically producing a severe pneumonia. Clinical suspicion for primary influenza pneumonia should be raised when symptoms persist and increase instead of resolving in a patient with acute influenza. High fever, dyspnea, and even progression to cyanosis can be seen.

Primary viral pneumonia is the most severe, although the least common, of the pneumonic complications of influenza. It has an apparent predilection for individuals who have elevated left atrial pressures, although it has also been described in patients with chronic pulmonary disorders, and rarely in apparently otherwise healthy young adults.

It is common for patients with influenza and a complicating pneumonia to have features of both viral and bacterial pneumonia. In these cases, patients may have either a gradual progression of illness or a transient improvement followed by worsening. Influenza virus as well as bacterial pathogens are usually present in the sputum. Pulmonary infiltrates, including areas of frank consolidation, may be noted by physical examination or chest radiograph.