This description is based on limited data, largely derived from clinical experience, published data, unpublished data from review of Mexican cases, and descriptions from WHO teleconference calls. Although several patient groups have been described (eg. COPD/asthma exacerbation, mild respiratory illness), this report describes the patient with acute pneumonitis.

Key features

• Patients may include younger, previously well adults, as well as the immunocompromised patient and pregnant women.
• Obesity appears to be a risk factor for respiratory failure
• Relatively rapid onset of disease, with a short duration from hospital admission to respiratory failure. This may depend on delay in presenting to hospital.
• Negative initial nasopharyngeal swabs have been reported, with diagnosis subsequently made on viral analysis of sputum, ET aspirate, or BAL
• Chest X-ray demonstrates bilateral patchy airspace disease, with rapid onset.
• Autopsy reports have described diffuse alveolar damage, pulmonary hemorrhage as well as multiple pulmonary emboli
• Patients have been very difficult to ventilate, with marked hypoxemia. Alternative forms of ventilation are often required, including APRV, HFO and iNO administration. ECMO has been used successfully.
• One group has reported patients to have little response of hypoxemia to PEEP, with a response to aggressive diuresis.
• Septic shock is uncommon, although many patients have required inotropic support and renal failure may occur.
• Improvement in pulmonary function has been slow, with many patients requiring ventilatory support for 3 weeks or more.
• Persistent viral excretion may occur despite treatment with antiviral agents, requiring prolonged therapy.
• Antiviral treatment has included oseltamivir PO and zanamavir by inhalation and IV.
• Secondary bacterial infection has not been common
• No significant reports of the use/effect of steroids.
• Death has occurred predominantly due to respiratory failure with progressive hypoxemia, unlike conventional ARDS.
• Mortality of patients requiring mechanical ventilation is in the range of 30 - 40%.