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29 Acute bronchitis and acute exacerbations of chronic airways disease
Bronchial infections with viral and bacterial microorganisms cause considerable morbidity, as well as economic costs incurred through health care and loss of productivity. These infections affect all age groups. An important consideration is whether or not an individual has underlying chronic lung disease, as that alters the etiology, clinical presentation, laboratory findings, and indications for therapy. In this chapter, we discuss acute infectious bronchitis in individuals without underlying chronic lung disease, before outlining approaches when an individual has an acute exacerbation of a chronic lung disease such as asthma, chronic obstructive pulmonary disease (COPD), or non-cystic fibrosis bronchiectasis.
Acute bronchitis
Acute bronchitis is a common condition in both children and adults. It has been defined as “an acute illness, occurring in a patient without chronic lung disease, with symptoms including cough, which may or may not be productive and associated with other symptoms or clinical signs that suggest LRTI [lower respiratory tract infection] and no alternative explanation (e.g., sinusitis or asthma).” Most people will experience this at some time during their lives, and in most cases it is self-limiting and will not result in those affected seeking medical attention.
Nonetheless, this condition is a frequent cause of attendance to primary care providers and has been identified as a potential target for reducing unnecessary antibiotic prescribing in the community. Additionally, those who seek medical care for acute bronchitis, especially if this is frequent, should be considered for investigation as to whether or not they have an underlying chronic airways disease.
Typical symptoms of acute bronchitis are the acute onset of cough with or without sputum production or discoloration, often preceded by or associated with upper respiratory tract symptoms such as sneezing, a runny nose, or a sore throat. The cough often lasts for 7 to 10 days but may persist for several weeks. Fever and wheezing are frequently associated, as is a burning sensation in the tracheal area. Some patients may have focal signs on chest auscultation. Abnormality of vital signs or the presence of focal chest signs suggesting consolidation should prompt consideration of a chest radiograph to exclude pneumonia.
Young infants may present with the syndrome of bronchiolitis. In addition to symptoms and signs above they may be off their food, and in severe cases, develop cyanosis or apnoea. Treatment may involve the use of nebulized adrenaline or hypertonic saline.
Acute bronchitis is usually a viral illness but it may also be caused by bacterial species including Mycoplasma pneumoniae, Chlamydia pneumoniae, or Bordetella pertussis amongst others. The relative frequency of implicated viral species varies with time, place, and patient age, with agents circulating in the community with epidemic-like characteristics. Common species include influenza, rhinovirus, coronavirus, and common pediatric pathogens such as respiratory syncytial virus, human metapneumovirus and parainfluenza virus.
Extensive investigation for a cause of acute bronchitis is not usually necessary or beneficial. While molecular testing (PCR) of upper respiratory tract secretions will often identify a viral pathogen, this finding seldom alters management. Limited investigation for specific pathogens may be of use in selected cases, such as for public or occupational health reasons during a whooping cough outbreak, or to decide on whether or not to offer influenza treatment in a suspected case.
Antibiotic treatment is commonly requested by patients with acute bronchitis, with wide variation in prescribing practice for this condition. There is observational evidence that antibiotic use may lead to a statistically significant but clinically nonsignificant reduction in symptom duration. Given the typically benign, self-limited course of the illness and increasing rates of antibiotic resistance in common bacterial pathogens, antibiotic use for this condition should be avoided. Unnecessary treatment also undermines the patient’s ability to self-manage this common condition in the future. Several methods exist for dealing with patients’ expectations of receiving antibiotics. These include education or printed information outlining the uncertainties involved, or the use of delayed prescriptions. This is where a prescription is given, to be used only under specific criteria which point to bacterial infection. Symptomatic treatment may be offered, but there is little evidence it alters any outcomes.
Treatment for influenza with a neuraminidase inhibitor may be appropriate in patients with a consistent illness during an epidemic, if the circulating strain is known to be susceptible to the available treatments and the patient has presented early enough in the course of their illness to derive a meaningful benefit. These medicines reduce the duration of symptoms by about 1 day but do not reduce rates of hospitalization or death.
Postviral bacterial pneumonia may occur following an episode of bronchitis, and may be severe. Investigation for this with a chest radiograph should be considered in patients who have deteriorated or failed to settle as expected. If pneumonia is confirmed, antibiotic treatment is appropriate and further microbiologic investigation may be required. Consideration should be given to specific cover for Staphylococcus aureus in patients with postinfluenza pneumonia.
Acute exacerbations of chronic airways disease
Disease definitions
The airways diseases asthma and COPD are relatively common, with each affecting 5% to 10% of people worldwide. By definition, asthma is a reversible airways disease characterized by steroid-responsive airways inflammation. It occurs in people with a genetic predisposition to develop allergic reactions to aeroallergens. In contrast, COPD is a persistent and progressive disease with an enhanced inflammatory response in the airways and the lungs to noxious particles and gases, such as smoke from cigarettes or fires. COPD as a disease entity encompasses patients with emphysema or chronic bronchitis. The latter term describes a clinical syndrome of chronic cough or sputum for 3 months in 2 consecutive years and should not be considered indicative of chronic infection. Instead, excess mucus is produced by goblet cells which have become hypertrophic due to the abnormal inflammatory response.
Bronchiectasis (BX) is a rarer condition which results in daily production of large amounts of sputum. It has a number of causes, including infection. BX is characterized by irreversible dilation of parts of the bronchial tree, resulting from destruction of the muscle and elastic tissue. The prevalence of BX is unknown but the condition is increasingly recognized in part because of greater use of chest CT scans.
It is increasingly recognized that chronic airways diseases may occur together: bronchial hyperreactivity may be a risk factor for COPD; COPD occurs in asthmatics who smoke; and BX may complicate severe asthma or COPD.
Common features of acute exacerbations
The role of infection in these three chronic airways diseases is discussed further below. All three are characterized by the occurrence of acute exacerbations (AEs) which may or may not be infective in origin. There are various definitions of AEs, but most are clinical, such as an acute worsening in the patient’s shortness of breath, and/or cough, and/or sputum beyond the baseline, sufficient to warrant a change in management. AEs are more frequent in the winter months, suggesting viruses play an important role.
The frequency of AEs increases with disease severity and correlates with poorer quality of life. In turn, AEs may have a role in accelerating decline in lung function and thus contribute to morbidity and premature mortality. In economic terms, the cost of AEs, especially hospitalizations, far exceeds that of stable chronic disease management; amounting to billions of dollars annually in the United States alone.
The pathologic and physiologic abnormalities of airways that predispose patients with chronic airways disease to bacterial infection include impaired mucociliary clearance, bronchial obstruction by abnormal secretions, and bronchoconstriction. In patients with COPD or BX, there are colonizing bacteria in the bronchial epithelium which may become pathogenic, as well as impaired host defenses. For example, there is reduction in bacterial phagocytosis, intracellular bactericidal activity by polymorphonuclear neutrophils, macrophage recruitment, and sputum immunoglobulin levels.
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