Microscopic and baceriologic analysis of expectorated sputum

Area of Science:

• Microbiology
• Clinical Diagnostics
• Respiratory Medicine

Background:

• Sputum analysis is crucial for diagnosing respiratory infections.
• Microscopic assessment of sputum quality is essential before bacterial culture.
• Contamination with oral flora can affect culture results.

Purpose of the Study:

• To evaluate the microscopic criteria for assessing sputum suitability for bacterial culture.
• To correlate the number of squamous epithelial cells (SEC) with bacterial load and contamination.
• To compare sputum culture results with transtracheal aspirates.

Main Methods:

• Gross and microscopic examination of expectorated sputum samples.
• Categorization of specimens based on leukocyte and squamous epithelial cell (SEC) counts under low-power microscopy (100x).
• Gram staining of smears to assess cellular content and bacterial flora.

Main Results:

• Specimens with >10 SEC/field yielded a mean of >4 bacterial species, often with oropharyngeal flora.
• Specimens with <10 SEC/field yielded a mean of 2.7 species and resembled transtracheal aspirates.
• Potential pathogens were found in <15% of specimens with >10 SEC/field.

Conclusions:

• Microscopic assessment of SEC count is a reliable indicator of sputum sample quality.
• Sputum with <10 SEC/field is more representative of lower respiratory tract bacterial flora.
• High SEC counts suggest oropharyngeal contamination, potentially masking true pathogens.