Respiratory tract infection Unusual infection by anatomical site Unusual lower respiratory tract infection Recurrent lower respiratory tract infections, including bronchiectasis, are characteristic of antibody deficiencies and combined immunodeficiencies. Increased susceptibility to infection of the lower respiratory tract, as manifested by recurrent or severe infection of the trachea, bronchi, bronchioles, or lung parenchyma, or by infection caused by an atypical or opportunistic organism.