Table 2– Aetiologies of rapid deterioration (RD; first episode)
AetiologyCases n (%)#Documented organisms (n)
Total RD163 (35.4)
Bilateral lesions140 (30.4)
 AE90 (19.5)
  Definite57 (12.4)
  Suspected33 (7.2)
 Infection37 (8.0)
  Definite21 (4.6)
   Bacterial9 (2.0)Streptococcus pneumoniae (2)MRSA (1)Haemophilus influenzae (4)Legionella spp. (1)Klebsiella pneumoniae (1)
   Viral7 (1.5)CMV (7; 2 mixed infections with RSV or Pneumocystis jiroveci)Influenza virus (1)RSV (1)
   Fungal2 (0.4)Candida spp. (1)Aspergillus spp. (1)
   Parasitic2 (0.4)Pneumocystis jiroveci (2)
   Mycobacterial1 (0.2)Mycobacterium tuberculosis (1)
  Suspected+16 (3.5)
 Heart failure5 (1.1)
 PTE2 (0.4)
 AEP1 (0.2)
 Uncertain§5 (1.1)
Focal lesion23 (5.0)
 Pneumothorax9 (2.0)
 Infection14 (3.0)Klebsiella pneumoniae (1)Klebsiella oxytoca (1)Streptococcus pneumoniae (1)
  • AE: acute exacerbation; PTE: pulmonary thromboembolism; AEP: acute eosinophilic pneumonia; MRSA: methicillin-resistant Staphylococcus aureus; CMV: cytomegalovirus; RSV: respiratory syncytial virus. #: percentage of total subjects (n = 461); : identified by culture, antigen test (for S. pneumoniae and Legionella), or direct fluorescence monoclonal antibody stain (for P. jiroveci); +: cases in which no organism was identified, but infection was clinically suspected due to symptoms such as grossly purulent sputum and rapid resolution of symptoms in response to antibiotics alone; §: cases in which no organism was identified, but the criteria for AE were not completely satisfied due to incomplete study.