What are the clinical forms of influenza pneumonia?

Updated: Mar 24, 2021
  • Author: Zab Mosenifar, MD, FACP, FCCP; Chief Editor: John J Oppenheimer, MD  more...
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Answer

The three clinical forms of influenza pneumonia are primary influenza pneumonia, secondary bacterial pneumonia, and mixed viral and bacterial pneumonia.

Primary influenza pneumonia manifests with persistent symptoms of cough, sore throat, headache, myalgia, and malaise for more than 3-5 days. The symptoms may worsen with time, and new respiratory symptoms, such as dyspnea and cyanosis, may appear. This form is the least common but the most severe in terms of pulmonary complications.

Secondary bacterial pneumonia is characterized by the relapse of high fever, cough with purulent sputum after initial improvement, and radiographic evidence of new pulmonary infiltrates. The most common pathogen is Streptococcus pneumoniae (48%), followed by Staphylococcus aureus, [58] Haemophilus influenzae, and Gram-negative pathogens.

Elderly persons may have a lower frequency of upper respiratory complaints. One study demonstrated that the triad of cough, fever, and acute onset had only a 30% positive predictive value, in contrast to 78% in young adults. Fever and altered mental status may be the only signs of influenza pneumonia in an older patient with chronic cognitive impairment. Gastrointestinal complaints and myalgia are more common in influenza than in RSV infection. [49, 59]

Avian influenza (H5N1) has an incubation period of 2-5 days, but symptoms may begin up to seven days after exposure. The primary initial symptom is fever, and symptoms of cough, malaise, myalgia, headache, sore throat, abdominal pain, vomiting, and diarrhea are also common. The gastrointestinal complaints may initially suggest gastroenteritis. When pneumonia develops, cough, followed by dyspnea, tachypnea, and chest pain, are reported. In severe cases, encephalitis/encephalopathy, cardiac failure, renal failure, multiorgan failure, and disseminated intravascular coagulation can occur. [60]

H1N1 influenza presents similarly to seasonal influenza. Fever and cough are almost universal symptoms. Shortness of breath (54%), fatigue/weakness (40%), chills (37%), myalgias (36%), rhinorrhea (36%), sore throat (31%), headache (31%), vomiting (29%), wheezing (24%), and diarrhea (24%) are the most common other symptoms.

Mixed viral and bacterial pneumonia is common and can manifest as a gradual progression of disease or as a transiently improving condition followed by a worsening one. Both bacterial pathogens and an influenza virus are isolated.


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