Diagnosis of Bacterial Tracheitis Direct laryngoscopy Characteristic x-ray findings Diagnosis of bacterial tracheitis is suspected clinically and can be confirmed by direct laryngoscopy, which reveals purulent secretions and inflammation in the subglottic area with a shaggy, purulent membrane, or by lateral neck x-ray, which reveals subglottic narrowing that may be irregular as opposed to the symmetric tapering typical of croup.