A positive culture, sputum means that pathogenic organisms are present. Clinically, the signs and symptoms of lower respiratory tract infections are also correlated. The result is considered negative if there is no growth of pathogenic organisms for 24 or 48 hours. The reason for negative results could be the absence of sufficient quantity of pathogen in the sample. It is also possible that other tests may be required for the detection of pathogenic organisms such as Sputum or Smear AFB or Culture fungus.