Although chronic bronchitis (CB) can be present in individuals with no known lung disease, up to three-quarters of patients with chronic obstructive pulmonary (COPD) can have CB, explains Spyridon Fortis, MD. “CB, accompanied by a chronic productive cough, results in increased mortality even in individuals with normal lung function,” he says, adding that “the association of CB and mortality seems to be present only in people with a history of smoking.”
In patients with COPD, CB is linked with poor HRQOL and accelerates decline in lung function, Dr. Fortis adds. “Patients with both COPD and CB also experience more frequent exacerbations and hospitalizations and have higher mortality relative to patients with COPD without CB,” he says.
For a study published in CHEST, Dr. Fortis and colleagues sought to clarify this correlation and determine if CB is linked with all-cause mortality. They conducted a systematic literature review and meta-analysis through a search of published articles.
Smoking Status of All Participants Assessed
A study was excluded if it included participants who demonstrated obstructive spirometry findings, was a duplicate report, did not define CB or mortality, included only participants with abnormal spirometry, did not report separately an association of CB and mortality in patients with non-obstructive CB, included participants with lung diseases such as COPD (not including asthma), had a less than 6 months follow-up date, was in a language other than English, or was a review, letter, or editorial. Of the 5,014 titles initially identified, eight fulfilled the criteria for inclusion (Table).
In addition to assessing the association between non-obstructive CB and all-cause mortality, Dr. Fortis and colleagues examined the association more specifically in persons who have never smoked (ie, never smokers) and those who currently smoke, formerly smoked, or both (ie, ever smokers).
Hazards ratios (HRs) within the included articles were pooled for non-obstructive CB and the study team used the random effects model and inverse variance weighting to obtain the summary effect estimate. Since some reports used a broad definition of CB that included dyspnea and wheezing, a stratified analysis was done.
A significant association was found between non-obstructive CB and all-cause mortality (HR, 1.37; 95% CI, 1.26 1.50). Statistically significant heterogeneity was not found (P=0.14; I2= 29%). In the studies that applied a broader definition of CB, non-obstructive CB was associated with increased mortality (HR, 1.28; 95% CI, 1.10- 1.48; I2 = 0%). In studies that applied a more specific definition of CB, non-obstructive CB was linked with increased mortality (HR, 1.40; 95% CI, 1.26-1.56), and moderate heterogeneity was identified (P=0.11; I2 =37%).
Non-Obstructive Chronic Bronchitis Linked With Higher Mortality in Smokers
In those identified as ever smokers, nonobstructive CB was associated with increased mortality (HR, 1.49; 95% CI, 1.35-1.64), and no heterogeneity was found (P=0.70; I2=0%). In those identified as never smokers, nonobstructive CB was not linked with increased mortality (HR, 1.22; 95% CI, 0.90-1.66), and moderate heterogeneity was found (P=0.10; I2=49%).
“Future research should investigate whether intervention in this population can reduce the increased mortality,” Dr. Fortis wrote. Another question that he hopes will be researched is: “Is the increased mortality in people with chronic
bronchitis and history of smoking due to progression to COPD?”
