Recent observations have clearly shown that therapeutic interventionscan, to some extent, prevent exacerbations as well as modify their course. This has created boththe opportunity and the imperative to develop more effective interventions to mitigate theburden of acute exacerbations, which, in turn, has created a need for precise and opera-tionally tractable definitions.

Short-termexposure to fine (PM2.5) and coarse (PM10) particulate matter is associated with increased hospitalizations, ER visits,and outpatient visits,(16) as well as increased mortality of COPD exacerbations.(15,17,18)

Exacerbations of COPD are important events in the management of COPD because they negatively impact healthstatus, rates of hospitalization and readmission, and disease progression.(2,3)

The SGRQ is the most widely documented comprehensive measure; scores < 25 are uncommon in diagnosed COPDpatients(43) and scores ≥ 25 are very uncommon in healthy persons.(44,45) Therefore, it is recommended that a symptomscore equivalent to SGRQ score ≥ 25 should be used as the threshold for considering regular treatment for symptomsincluding breathlessness, particularly since this corresponds to the range of severity seen in patients recruited to thetrials that have provided the evidence base for treatment recommendations.

The CAT™† is an 8-item questionnaire that assesses health status in patients with COPD (Figure).(41) It was developedto be applicable worldwide and validated translations are available in a wide range of languages. The score rangesfrom 0 to 40, correlates very closely with the SGRQ, and has been extensively documented in numerouspublications.(42)

The onset, or prodrome,of COPD exacerbations is a subject that has received very littlestudy to date.

In contrast, in this study,we focused on exacerbation risk prediction for discharged COPDpatients, because their health condition is likely to be lessaccessible.

These resultsshowed that physiological and environmental data are morepowerful predictors than questionnaire data.

However, when predicting risk of fu-ture exacerbations based on previousevents, the positive predictive value re-mains low,9 indicating that additionaldeterminants of exacerbation suscep-tibility remain to be identified

COPD exacerbations are more common in females, patients with car-diometabolic or psychiatric comorbidities—in particular depression—and at the mostsevere spectrum of the disease. A history of prior exacerbations has been demonstrated tohave by far the strongest association with the risk of future exacerbations [7,8]

Seasonality isknown to affect COPD exacerbations, most frequently occur-ring in the winter months,37–39 which is likely to reflect anincreased prevalence of respiratory infections, reduced immu-nity, altered environmental conditions, and physiologicalresponses during these months.40,41

Neither the developmental nor the validation datasetsincluded patients with mild (GOLD 1) severity and, assuch, we could not establish the accuracy of predictionsfor this subgroup.

Azithromycin reduces annual exacer-bation rate by 27%.8

Severe exacerbations are especially important asthey are associated with rapid decline of lung functionand 50% of patients die within 2 years after admissionto hospital.

Prevention, early detection, and appropriate treatment ofexacerbations are a focal point of attention in COPD careand research.