Adenovirus Type 7 causing severe lower respiratory tract infection in immunocompetent adults: a comparison of two contrasting cases from an intensive care unit in North West England

•Severe lower respiratory tract adenovirus infection requiring critical care admission is rare in immunocompetent adults.•Evidence concerning diagnosis and management of immunocompetent adults with adenovirus severe lower respiratory tract infection (sLRTI) is limited.•We present rare cases of severe lower respiratory tract adenovirus infection in immunocompetent adults, on a critical care unit.•Immunocompetent patients with adenovirus sLRTI may present with pneumonitis and acute respiratory distress syndrome (ARDS)•Clinical features of sLRTI are difficult to distinguish clinically and radiologically from other causes of pneumonitis, including severe influenza.