The general symptoms cough for more than 10 days and fever for more than 3 days can indicate the presence of occult pneumonia, just as a temperature of 39 °C or higher and a high white blood cell count. 
Administration of a pneumococcal vaccine decreases the incidence of occult pneumonia, which suggests that Streptococcus pneumoniae is a cause of occult pneumonia. Occult pneumonia, however, can also be the result of atypical pneumonia. 
- C.G. Murphy et al. Clinical predictors of occult pneumonia in the febrile child. Acad. Emerg. Med. 14(3), 243–249 (2007) PMID 17242382.
- Commission on Acute Respiratory Diseases, Fort Bragg, North Carolina Primary Atypical Pneumonia American J. of Public Health, April, 1944; Vol. 34
- M.S. Rutman, R. Bachur, M.B. Harper Radiographic pneumonia in young, highly febrile children with leukocytosis before and after universal conjugate pneumococcal vaccination. Pediatr Emerg Care. 2009 Jan;25(1):1-7
- Ioanna Ramoutsaki, Ioannis Ramoutsakis and Demosthenes Bouros Pneumonology or Pneumology? PDF  CHEST, May 2002 vol. 121 no. 5 1385-1387; doi:10.1378/chest.121.5.1385
- van Dale, Etymologisch woordenboek; 1ste dr., 1989