Is Bronchitis Contagious?
Yes, acute bronchitis is contagious because it is caused by infectious agents—primarily respiratory viruses in over 90% of cases—that spread from person to person through respiratory droplets. 1
Understanding the Infectious Nature of Acute Bronchitis
Viral Causes (Highly Contagious)
The vast majority of acute bronchitis cases (≥90%) have a viral etiology, making them inherently contagious: 1
- Lower respiratory tract viruses include influenza A and B, parainfluenza, and respiratory syncytial virus (RSV), which spread rapidly through communities 1
- Upper respiratory tract viruses such as rhinovirus, coronavirus, and adenovirus also cause acute bronchitis and are easily transmitted 1
- RSV shows particularly high attack rates in households with small children and institutional settings, with clinical attack rates reaching 61.2% and serologic rates of 75% 1
- Influenza occurs in distinct yearly outbreaks with rapid community spread, causing considerable morbidity 1
Bacterial Causes (Less Common but Still Contagious)
Only 5-10% of acute bronchitis cases have bacterial causes, but these organisms are also transmissible: 1
- Bordetella pertussis (whooping cough) is highly contagious and accounts for up to 25% of adults with nonspecific lower respiratory symptoms 2
- Mycoplasma pneumoniae and Chlamydophila pneumoniae cause outbreaks in close-contact settings like military barracks and college campuses, with mixed viral-bacterial infections occurring in up to 36% of outbreak cases 1
Transmission Patterns and Contagious Period
The contagious period typically aligns with the acute symptomatic phase, particularly when cough is most prominent: 1
- Patients are most contagious during the first week of illness, when 66% seek medical care 1
- Viral shedding occurs primarily through coughing, which is present in 83-93% of cases within the first 2 days 1
- The infection spreads through respiratory droplets generated by coughing and sneezing 1
Important Clinical Distinction: Chronic Bronchitis is NOT Contagious
Chronic bronchitis itself is not an infectious or contagious condition—it results from prolonged exposure to pulmonary irritants, primarily cigarette smoke: 1
- Chronic bronchitis is defined as cough with mucus production on most days for 3 consecutive months over 2 successive years 1
- However, patients with chronic bronchitis frequently experience acute infectious exacerbations superimposed on their chronic condition, and these exacerbations can be contagious if caused by viral or bacterial pathogens 1
Key Clinical Pitfalls
Do not confuse acute bronchitis with non-infectious conditions that present similarly but are not contagious: 1
- Asthma is misdiagnosed as acute bronchitis in approximately one-third of patients presenting with acute cough 1
- The common cold shares many symptoms with acute bronchitis, making clinical distinction difficult or impossible at times 1
- Patients with recurrent "acute bronchitis" episodes (≥2 in 5 years) have a 65% probability of actually having mild asthma, which is not contagious 1
Practical Implications for Infection Control
Given the highly contagious nature of acute bronchitis: 1
- Respiratory precautions are appropriate during the acute symptomatic phase
- Hand hygiene and covering coughs reduce transmission of viral and bacterial pathogens 1
- Isolation considerations are particularly important for healthcare workers and those in contact with vulnerable populations (elderly, infants, immunocompromised) 1, 2
- Pertussis treatment with erythromycin may be indicated for patients in frequent contact with unimmunized infants to reduce transmission 2