Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1431 page)

THROAT AND PHARYNGEAL CULTURE, PATIENTS WITH CYSTIC FIBROSIS

   Use

   This culture is used to screen for the bacterial pathogens that commonly cause lower respiratory tract infections in patients with CF. Pharyngeal specimens are most useful to document carriage/chronic infection, whereas lower respiratory specimens are recommended for the evaluation of clinically evident, acute infection.

   Pneumonia is a cause of significant morbidity and mortality in patients with CF. The etiology of these infections is different than that seen in other patient groups.
P
.
aeruginosa
(including mucoid variants),
Burkholderia cepacia
complex organisms,
Stenotrophomonas maltophilia
,
H
.
influenzae
, and other glucose-fermenting and nonfermenting gram-negative bacilli, as well as mycobacteria,
S
.
aureus
, and
S
.
pneumoniae
, are commonly isolated from lower and upper respiratory tract specimens submitted from patients with CF.

   Sputum from patients with CF should not be screened by Gram stain, as recommended for routine sputum cultures submitted from patients without CF.

   
Special collection and transport instructions:

   Posterior pharyngeal swabs may be submitted.

   Expectorated sputum or invasively obtained lower respiratory specimens are recommended for evaluation of chronic carriage/infection and acute exacerbation of pulmonary infection.

   Specimens are transported as for routine sputum specimens.

   Method:

   A variety of supportive, selective, and differential agar media are inoculated. Commonly inoculated media include

   SBA as a supportive medium capable of supporting the growth of many pathogens, including
S
.
pneumoniae
.

   CNA agar for gram-positive pathogens; mannitol–salt agar for isolation of
S
.
aureus
.