Experience with a microscopic screening program for sputum specimens

Area of Science:

• Clinical Microbiology
• Respiratory Diagnostics

Background:

• Sputum specimen quality is crucial for accurate bacterial identification and antimicrobial susceptibility testing.
• High levels of squamous epithelial cells (SEC's) often indicate oropharyngeal contamination, potentially leading to misleading results.
• Leukocyte (polymorphonuclear leukocyte - PMN) counts can suggest inflammation and infection.

Purpose of the Study:

• To evaluate the impact of microscopic sputum specimen screening on the rate of acceptable samples for culture.
• To determine the correlation between microscopic cell counts (PMNs and SECs) and the likelihood of identifying pathogens.

Main Methods:

• Microscopic examination of nearly 2,000 sputum specimens at low magnification (X100).
• Categorization of specimens into 6 groups based on leukocyte (PMN) and squamous epithelial cell (SEC) counts.
• Bacteriologic evaluation including pathogen identification and antimicrobial susceptibility testing.
• Implementation of a screening program rejecting specimens with >25 SECs.

Main Results:

• Specimens with >25 PMNs and <25 SECs yielded potential pathogens in 51% of cases.
• Specimens with >25 SECs showed pathogen identification rates of only 19%.
• Specimens with <25 PMNs and <25 SECs had a 13% pathogen identification rate.
• The percentage of acceptable specimens nearly doubled after implementing the >25 SECs rejection criterion.

Conclusions:

• Microscopic screening of sputum for SECs is an effective method to improve specimen quality for culture.
• Implementing a threshold for SECs significantly increases the yield of relevant pathogens.
• This quality control measure enhances laboratory efficiency and diagnostic accuracy for respiratory infections.