Evaluation of three methods for culturing alginate throat swabs from cystic fibrosis patients

Deep throat swabs are usually cultured for potential respiratory pathogens in patients with cystic fibrosis (CF) who do not produce sputum. Using alginate swabs, three methods were examined in the present study: (i) semiquantitative processing (direct plating); (ii) mere elution of swabs in Ringer's lactate followed by plating of the eluate; and (iii) complete quantitative processing (elution plus two-step dilution series). Throat swabs from 56 CF patients yielded 122 isolates of potential respiratory pathogens. Semiquantitative processing (n = 101 isolates) was not significantly inferior to elution (n = 104) and quantitative processing (n = 113; p > 0.05). Since semiquantitative processing is the simplest method, it is to be preferred, provided that alginate swabs are used.