Bacterial tracheitis, also known as "bacterial croup," "acute laryngotracheobronchitis," or "membranous croup," is a potentially lethal infection of the subglottic trachea. It is often a secondary bacterial infection preceded by a viral infection affecting children most commonly under age six. Concern for airway protection is the mainstay of treatment as thick, mucopurulent secretions can cause airway narrowing. Treatment is aimed at protection of the airway, assessing the need for endoscopy for therapeutic and/or diagnostic reasons, and antimicrobial therapy.
Bacterial tracheitis is a bacterial infection of the trachea often preceded by a viral upper respiratory infection. Most common viruses implicated include Influenza A and B (with type A being the most common), respiratory syncytial virus (RSV), parainfluenza virus, measles virus, and enterovirus. These viruses cause airway mucosal damage via a local immune response which predisposes the trachea to the seeding of bacterial infections. Children affected are usually healthy. However, at-risk populations including immunocompromised individuals are prone to severe sequelae. Implicated bacteria include Staphylococcus aureus (most common, including MRSA), Streptococcus pneumoniae, Streptococcus pyogenes, Moraxella catarrhalis, Haemophilus influenzae type B, and less commonly, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia, and anaerobic organisms.
Bacterial tracheitis has a peak incidence between the ages of three to eight years, although it has been described less commonly in infants and adults. Males have a slight predominance over females with a 1.3:1 prevalence ratio. Annual incidence is rare with an estimated incidence of 0.1 cases per 100,000 children. Incidences are more common in fall and winter months than in summer or spring. This coincides with the typical seasonal viral epidemics of influenza, parainfluenza, and respiratory syncytial virus (RSV).
In bacterial tracheitis, opportunistic bacteria invade damaged tracheal mucosa and stimulate local and systemic inflammatory responses. Local responses cause edema, thick mucopurulent secretions, ulceration, and mucosal sloughing, which can predispose to subglottic narrowing. Systemic inflammation leading to sepsis is rare but can occur in immunocompromised children. S. aureus has been the most commonly implicated pathogen, although reports suggest Moraxella catarrhalis is becoming more common especially in younger children.
Microscopic Gram stain analysis of tracheal secretions usually reveals neutrophilia and bacteria identification. Often, bacterial tracheitis is polymicrobial. Infection of the tracheal mucosa causes local inflammation, swelling, thick exudates, pseudomembranes, and necrosis of the larynx, trachea, and mainstem bronchi.
Bacterial tracheitis was first described in medical literature in the 1920s despite the name not being coined until much later. The disease was initially referred to as acute laryngotracheobronchitis. Presentation occurs in two primary ways including a more insidious development with prodromal symptoms that suggest a viral respiratory tract infection. These are present for 1 to 3 days until the more severe development of airway deterioration occurs due to an overlapping bacterial infection. Less commonly, fulminant respiratory distress with less than 24 hours of symptoms can occur. These children tend to be more toxic appearing. Signs and symptoms include stridor (inspiratory or expiratory), fever, exudative cough, and respiratory distress. Drooling and tripoding are less common and suggest an alternative diagnosis such as epiglottitis, as children with bacterial tracheitis do not have difficulty swallowing their oral secretions. Patients with severe subglottic obstruction may have cyanosis, appear lethargic or can be combative suggesting hypoxemia and/or hypercarbia.
The diagnosis of bacterial tracheitis is clinical with a thorough history and physical examination. Children may appear febrile, toxic-appearing, and in respiratory distress. Trial with nebulized epinephrine and glucocorticoids will fail to show improvement in the patient's clinical course. Laboratory investigation with white blood cell count is variable and nonspecific. Leukocytosis, as well as mild leukopenia, are commonly seen. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are also nonspecific but are estimated to be elevated in 68% of patients. Blood cultures are rarely positive, however, should be obtained with suspicion for sepsis or in the immunocompromised. Radiographic images of the lateral or anteroposterior neck show tracheal narrowing, typical of that seen with croup. Less commonly, irregularity or haziness of the tracheal mucosal wall can also be seen on lateral neck radiographs. This has been referred to as the "candle dripping" sign. The epiglottis should appear normal. The tracheal air column can sometimes be visualized with atypical clouding. Airway stabilization should be a priority before obtaining imaging in patients with severe respiratory compromise. Chest radiographs commonly show findings suggestive of pneumonia, reported in roughly 50% of cases. Presence of concomitant pneumonia increases the severity of disease and the probability of endotracheal intubation.
Definitive diagnosis is made by direct visualization, although is not necessary with strong clinical suspicion. Bronchoscopy allows visualization of the infected airway and will demonstrate a normal or mildly erythematous epiglottis and an erythematous, edematous trachea with thick mucopurulent exudates. Bronchoscopy is performed with either a rigid or flexible endoscope, with the former suggested for suctioning the exudations to provide transient relief of airway obstruction as well as obtain specimens for culture. The decision to undergo bronchoscopy is made on a clinical severity basis. More severe cases benefit from the therapeutic stripping of membranes or exudates to provide relief of secretion obstruction. Exudates can be thick secretions or pseudomembranous that adhere to the tracheal wall. Flexible bronchoscopy is an alternative for those patients with the less severe presentation. However, those patients without severe respiratory distress, hypoxia and with minimal tracheal abnormalities on radiograph can be managed without bronchoscopy. Exudative secretions can extend distally to the mainstem bronchi. If bronchoscopy is performed, specimens for gram stain and cultures should be obtained during this time. Less severe cases not requiring endoscopy or endotracheal intubation can obtain cultures via sputum sample.
Diagnosis of bacterial tracheitis can be difficult given its rarity, in addition to more prevalent diseases with similar presentations. Epiglottitis can also present with fever, upper airway obstruction, and toxic appearance. However, these patients often present with drooling and preference for the tripod position which is uncommon in bacterial tracheitis. Croup can also present with stridor and similar radiographic presentation with subglottic narrowing ("steeple" sign). Bacterial tracheitis can be a complication of croup and should be suspected if therapeutic interventions such as nebulized racemic epinephrine or steroids do not improve the clinical course. Peritonsillar or retropharyngeal abscesses will demonstrate fever, drooling, muffled voice changes and pharyngeal pain with limited mobility of the neck. Other diseases that can mimic bacterial tracheitis include foreign body aspiration, diphtheria, and severe bacterial pneumonia.
Treatment of bacterial tracheitis includes a prompt assessment for airway compromise. The need for intubation is common and is required in an estimated 72% to 75% of patients. This procedure can be difficult secondary to airway edema, and it is recommended to be performed in the operating room or intensive care unit setting by the most experienced provider available. Hypoxia, respiratory muscle retractions, fatigue, altered mental status and decreased breath sounds are signs indicative of impending airway failure. Younger children with smaller airways are at higher risk for the need for airway stabilization. If intubation is indicated, endotracheal tubes one or two sizes smaller should be selected due to airway narrowing. Placement into the ICU after intubation should serve to provide close monitoring and frequent suctioning of the endotracheal tube. In one case series, average intubation duration was reportedly 3.2 days. Extubation should be considered in those with clinical improvement, reduced tracheal secretions, and development of an air leak around the endotracheal tube. Other treatments in less severe cases include supplemental humidified oxygen, racemic epinephrine trial, and avoiding patient agitation which can worsen an already compromised airway.
Antibacterial management should be prompt and include broad coverage, including MRSA. Gram stain results, if obtained, can focus antibiotic selection but broad coverage should be initially chosen until culture results are obtained. Current guidelines recommend a 10-day to 14-day antibiotic course, although no formal studies have investigated the recommended time length of antimicrobial treatment. First-line treatment has been suggested to include ceftriaxone plus nafcillin or vancomycin or clindamycin plus a third-generation cephalosporin or ampicillin-sulbactam. For patients with beta-lactam antibiotic severe allergy, the recommended antibiotic treatment regimen includes vancomycin or clindamycin plus levofloxacin or ciprofloxacin. Glucocorticoids have not been shown to alter clinical course or patient outcomes. Antiviral therapy may be beneficial if a preceding viral etiology is determined to be influenza and symptoms have been present for less than 48 hours.
Mean duration of hospitalization is estimated to range from 3 to 12 days. Most children recover without debilitating sequelae with the tracheal mucosa fully healing without permanent damage. However, subglottic stenosis has been reported secondary to endotracheal intubation with an inflamed airway. Mortality has been estimated in 2% to 3% of patients due to primary respiratory failure with cardiac arrest, cerebral anoxia, acute respiratory distress syndrome (ARDS), pulmonary edema, pneumothorax, toxic shock syndrome, and septic shock. These incidences are rare with septic shock seen in 2% to 6%, cardiorespiratory arrest in 2% to 3%, ARDS in 1% to 3% and the remainder of complications listed in one percent or less of patients. Prevention is aimed at vaccination against viral syndromes (measles and influenza) and pneumococcus, especially in immunocompromised children.