Table 2.

Clinical presentations and diagnostic features of severe influenza A pneumonia

	Influenza Pneumonia	Influenza withSimultaneous Bacterial CAP	Influenza Followed by Sequential Bacterial CAP
Usual pathogen	Influenza Aa	Influenza A withStaphylococcus aureus (MSSA/CA-MRSA) CAP	Influenza A followed byStreptococcus pneumoniae or Haemophilus influenzae CAP
Presentation of CAP	Subacute/acute	Acute	Influenza then an interval of clinical improvement (5–7 days) followed by CAP
Symptoms	Severe myalgias (neck/back)Debilatating fatigueRetro-orbital painDry cough (± mild hemoptysis)Shortness of breath ± pleuritic chest pain	Same as influenza A plus hemoptysis, productive cough/purulent sputum ± pleuritic chest pain	After 5–7 days following influenza, new fevers and productive cough/purulent sputum ± pleuritic chest pain
Signs	FeverConjunctival suffusion Dyspnea (± cyanosis) No rales	Same as influenza plus localized rales ± consolidation	Localized rales ± consolidation
Laboratory tests	Hypoxemia (A-a gradient >35)Relative lymphopenia Thrombocytopenia± Leukopenia Sputum: WBC with normal/or no flora	Same as influenza plus LeukocytosisSputum: WBCs with Gram + cocci (in clusters)	Minimal/no hypoxemia (A-a gradient <35)LeukocytosisSputum: WBCs with Gram + cocci (in pairs) or GNBs
Chest radiograph	No infiltrates (early)Bilateral patchy interstitial infiltrates (later) No/small pleural effusion(s)	Focal segmental/lobar infiltrates with rapid cavitation <72 h	Focal segmental/lobar infiltrates without cavitation ± consolidation± pleural effusion
Mortality	+++	++++	+

Abbreviations: A-a, alveolar arterial gradient; CAP, community-acquired pneumonia; GNBs, gram-negative bacilli; MRSA, methicillin-resistant S aureus; MSSA, methicillin-sensitive S aureus; WBC, white blood cell count.

Data from Cunha BA. Pneumonia essentials. 3rd edition. Sudbury (MA): Jones & Bartlett; 2010.

^aUncomplicated influenza is a 3-day illness.