Sinusitis after radiation is caused by resistant bacteria

Plain x-ray showing opacification of right maxillary sinus

Patients who undergo radiotherapy for nasopharyngeal carcinoma tend to suffer from sinusitis because irradiation causes damage to sinonasal tissue. There is very little information about the organisms causing sinusitis after radiation therapy. Two recent studies from China provided important information about the unique microbiology of sinusitis in these patients.

Huang et al (Am J Rhinol. 2007) endoscopically obtained specimens from 25 patients with acute sinusitis that developed sinusitis after irradiation therapy. Staphylococcus aureus comprised 42% and Gram-negative bacilli 36% of all aerobic isolates. The main anaerobic isolates were Peptostreptococcus and Veillonella spp. Polymicrobial infections and beta-lactamase-producing pathogens were highly prevalent.

A study by Deng and Tang ( Eur. Arch.Otolaryngolog, 2009) compared the bacteriology of chronic maxillary sinusitis that developed after radiation therapy to chronic sinusitis in non irradiated individuals. Thirty people with each condition were evaluated using cultures for aerobic bacteria.

The most common isolates in the post irradiation chronic sinusitis group was S. aureus while those in the other group were Haemophilus influenzae, and Pseudomonas aeruginosa. The isolation rate of gram-positive cocci in the post irradiation group was higher than in the non irradiated patients. (62.5% compared with 30%, respectively; P < 0.05). In contrast the isolation rate of gram-negative bacilli in the irradiated patients was lower than in non-irradiated patients (31% compared with 70%, respectively; P < 0.05).

The findings of both studies illustrate the high rate of recovery of S. aureus from sinus aspirates of individual who were irradiated for head and neck cancer. Because of the high prevalence of methicillin resistant S. aureus (MRSA) these individuals may need to be treated with antimicrobials effective against these organisms.

These studies underscore the need to obtain appropriate cultures from patients with chronic sinusitis who were irradiated so that proper antimicrobials can be administered to them.