Paranasal sinuses including antral washings

Sinus samples are obtained by surgery. One of the most common samples is “antral washings” from the maxillary sinus where volumes of saline are used to wash out sinus contents.

Acute sinusitis commonly involves upper respiratory tract organisms such as S. pneumoniae, H. influenzae, M. catarrhalis and Group A streptococcus. S. aureus, B. cepacia and P. aeruginosa are also potential pathogens especially in immunocompromised patients. Anaerobic and fungal cultures are done on request only.

Nasal and nasopharyngeal specimens are unacceptable for diagnosis of sinusitis and are cultured for Staphylococcus aureus colonization only.

Setup Most sinus samples are saline washings and very thin in consistency. These are centrifuged for 10 minutes at 3000 RPMs and resultant sediment used for smears and media inoculation.

Direct examination

Gram stain


Media Incubation
Blood Agar (BA) CO2, 35°C x 48 hours
Chocolate Agar (CHOC) CO2, 35°C x 48 hours
MacConkey Agar (MAC) O2, 35°C x 48 hours

If fungi requested, add:

Sabouraud’s Heart Infusion Agar (SABHI) O2, 30°C x 4 weeks
SABHI with Chloramphenicol (SABHI-C) O2, 30°C x 4 weeks

If anaerobes are requested, add:

Wilkins Chalgren Agar (WC) AnO2, 35°C x 48 hours
WC Nalidixic acid – Tween 80 (NAT) AnO2, 35°C x 48 hours
WC Nalidixic acid – Vancomycin (NAV) AnO2, 35°C x 48 hours

Interpretation Examine the BA, CHOC and MAC plates after 24 and 48 hours incubation and, if applicable the WC, NAT and NAV after 48 hours incubation and identify all usual pathogens.

A wide array of unusual organisms have been occasionally isolated so a moderate to heavy pure growth of any organism should raise suspicion and prompt consultation with the lead technologist or microbiologist.


Gram stain

Report with quantitation the presence of pus cells and organisms.


Negative report
“Normal oral flora” or “No growth”.
“No anaerobes isolated” if anaerobic culture is requested.

Positive report
Quantitate and report significant isolates with appropriate sensitivities. Report “Normal oral flora” if also present.

References P.R. Murray, E.J. Baron, M.A. Pfaller, R.H. Yolken. 2003. Manual of Clinical Microbiology, 8th ed. ASM Press, Washington, D.C.

H.D. Izenberg. 2003. Nasal Sinus Cultures, in Clinical Microbiology Procedures Handbook, 2nd ed. Vol.1 ASM Press, Washington, D.C.