The Proportional Venn Diagram of Obstructive Lung Disease. Part 6
In the subpopulation of participants aged > 50 years, the prevalence of current asthma was 5.1%, the prevalence of current chronic bronchitis was 5.8%, and the prevalence of ever having had emphysema was 5.0% in the US NHANES III survey. In the UK GPRD subpopulation of participants aged > 50 years, the prevalence of current asthma was 1.6%, the prevalence of current chronic bronchitis was 1.1%, and the prevalence of current emphysema was 1.1% (data not shown). The seven mutually exclusive disease groups of this proportional Venn diagram also can be displayed as stacked bars, for comparison by gender and age (Fig 3). The relative size of the asthma-only group decreased with increasing age, both in women and men in the United States and the United Kingdom. In the NHANES III data, probably because acute bronchitis could have been misclassified as chronic bronchitis in some cases via the self-reported questionnaire, combinations of chronic bronchitis with asthma or chronic bronchitis alone appeared at very young ages. Emphysema was reported consistently from age 50 years onward. Combinations of two of the three OLD conditions occurred among 21.2%, 31.4%, and 14.4%, in those patients in the age groups of 60 to 69 years, 70 to 79 years, and > 80 years, respectively.
By contrast, in the UK GPRD, emphysema and chronic bronchitis are virtually nonexistent diagnoses before 50 years of age. After age 50 years, the frequent diagnoses of chronic bronchitis and emphysema together as COPD gave little room for chronic bronchitis-only or emphysema-only diagnoses. Therefore, combinations of two of the three OLD conditions occurred among 41.5%, 58.8%, and 65.5% of patients in the age groups of 60 to 69 years, 70 to 79 years, and > 80 years, respectively.
Finally, according to the spirometry data of NHANES III, US OLD participants with chronic bronchitis or emphysema, with or without a concomitant diagnosis of asthma, differed widely regarding the prevalence of airflow obstruction among patients with a diagnosis of emphysema only, with only 37.4% of patients having airflow obstruction confirmed by spirometry. The prevalence of airflow obstruction was significantly higher among participants with combinations of emphysema and chronic bronchitis (57.7%), with emphysema and asthma (51.9%), and with all three OLD diseases concomitantly (52.0%). Among all NHANES III participants with airflow obstruction, accounting for 4.8% of the general population, 58.3% reported no diagnosis of any of the three OLD conditions (Fig 4). The patterns of airflow obstruction prevalence were confirmed when the analysis was restricted to participants aged > 50 years (Fig 5). The prevalence of airflow obstruction in the seven mutually exclusive areas were as follows: asthma only, 26.5%; chronic bronchitis only, 29.6%; emphysema only, 45.5%; asthma plus chronic bronchitis, 55.8%; asthma plus emphysema, 48.7%; chronic bronchitis plus emphysema, 59.7%; and asthma plus chronic bronchitis plus emphysema, 49.0%. Still, 9.3% of the NHANES III population who were > 50 years of age had objective airflow obstruction without any respiratory diagnoses.
The Proportional Venn Diagram of Obstructive Lung Disease. Part 5
Before testing, screening questions were asked to determine medical safety exclusions (ie, those who had undergone chest or abdominal surgery within 3 weeks or had experienced heart problems [myocardial infarction or heart attack, angina or chest pain, and congestive heart failure]) within 6 weeks before attending the MEC. Airflow obstruction was defined as stage 1 according to the following Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines: FEV1, < 80% of predicted (based on gender, age, and height); FEVj/FVC ratio, < 70%.4 As children aged < 7 years did not have spirometry measurements recorded in NHANES III, estimates of airflow obstruction were weighted to the sample of participants aged > 8 years for whom spirometry had been measured.
Statistical Analysis
The prevalence for each condition per gender and age group is presented for the United States and the United Kingdom separately. Values have been extrapolated to the total population in each country using the NHANES III sample weights for the United States and using the Office of National Statistics data for the United Kingdom. Each graphic representation in Figures 2 to 5 was calculated by applying simple proportional euclidean geometry, with the area of the circle representing the exact population size. The areas of intersection of circles represent the percentage of overlap of two or three OLD conditions. Analyses were conducted using a statistical software package (SAS, version 8.0; SAS Institute; Cary, NC).
Results
The descriptive characteristics of NHANES III and GPRD participants with OLD are presented in Table 1. Patients were stratified into seven mutually exclusive disease groups by age and sex for each study population. Patients with asthma, in whom diagnoses had been made with or without other OLD conditions, were younger than COPD patients. The combination of asthma with chronic bronchitis, but not with emphysema, was associated with younger age.
In the US NHANES III total population, the prevalence of current asthma was 5.5%, the prevalence of current chronic bronchitis was 3.2%, and the prevalence of ever having had emphysema was 1.5%. In the UK GPRD total population, the prevalence of current asthma was 2.3%, the prevalence of current chronic bronchitis was 0.5%, and the prevalence of current emphysema was 0.5% (Fig 2). The asthma-only group was the largest group of OLD patients, accounting for 4.3% and 2.2%, respectively, of the United States and United Kingdom general populations; that is, 50.3% and 79.4%, respectively, of all OLD patients. Seventeen percent of OLD patients in the United States had more than one OLD condition, and 2.8% had all three conditions simultaneously. The UK figures were 19.1% and 3.6%, respectively. The areas of intersection among the three OLD conditions differed by data source and country (Fig 2).
The Proportional Venn Diagram of Obstructive Lung Disease. Part 4
Such patients often are referred to in the United States as having asthmatic bronchitis or the asthmatic form of COPD. Persons with chronic bronchitis and/or emphysema without airflow obstruction (ie, subsets 1, 2, and 11) are not classified as having COPD. Patients with airway obstruction due to diseases with known etiology or specific pathology, such as cystic fibrosis or obliterative bronchiolitis (subset 10), are not included in this definition. Reprinted with permission from the American Thoracic Society. of a hospital or other specialist visit (ie, inpatient, outpatient, or in an accident and emergency unit) must be recorded when the GP is informed. The diagnosis, symptoms, procedure or investigation, referrals, and their outcome must be entered into the relevant sections of the medical record. In this report, estimates are presented for patients who attended their GP, were given a diagnosis of asthma or COPD, and were registered throughout 1998. Pulmonary function data are not systematically or routinely available.
Case Definitions
Definitions of OLD in each database differ. NHANES III was a survey, and the questionnaire part of the survey asked participants about self-reported physician-diagnosis of three conditions (ie, asthma, chronic bronchitis, and emphysema). A positive response to the single question “Has a doctor ever told you that you have emphysema?” was sufficient to define emphysema. But, for asthma and chronic bronchitis, positive responses to the following two questions were necessary to define a current condition: “Has the doctor ever told you that you have [asthma or chronic bronchitis]?” and ”Do you still have it?“ A participant could be classified as having ah three conditions.
The GPRD system uses the Oxford Medical Information System (OXMIS) and READ coding system (the first three digits of the OXMIS number corresponds, in most cases, to the first three digits of the International Classification of Diseases, eighth revision, codes). Physician-diagnosed asthma, chronic bronchitis, and emphysema were defined as any individual who was labeled with one or more of the OXMIS/READ codes that were compatible with their respective diagnoses during calendar year 1998. This permitted the use of terms like COPD without reference to chronic bronchitis or emphysema. Acute bronchitis was excluded from the algorithm. The choice of GPRD OXMIS/ READ codes was recorded by each individual GP without instructions or guidelines. Direct codes for COPD were defined as overlapping chronic bronchitis and emphysema in the Venn diagrams.
Spirometry in NHANES III
Lung function testing was conducted on participants aged > 8 years by a trained technician in a mobile examination center (MEC). Testing also was conducted at the home of participants aged > 60 years who were unwilling or unable to come to the MEC.
Top Ten List in Ventilator-Associated Pneumonia (Part 5)
This study tested the potential value of routine microbiological cultures before VAP onset in predicting the causative pathogen of VAP and in anticipating the correct antibiotic choice. Authors cultured blood, respiratory secretions, catheter-tips, urine, and others substances, and found that there was no relationship between the colonization of tissues other than from the lungs and the etiology of VAP. High-quality distal bronchial samples obtained by BAL and protected-specimen brush, if cultured in the previous 72 h, had positive predictive values of 25% and 28%, respectively. Only distal respiratory secretions, when repeated at intervals between 48 and 72 h, might have a role in predicting the causative bacteria of VAP. Special attention is required for potentially drug-resistant bacteria like methicillin-resistant Staphylococcus aureus, P aeruginosa, and Acinetobacter baumannii with positive predictive values of 62%, 52%, and 24%, respectively. Previous colonization with any of these pathogens implies a high risk for subsequent pneumonia, allowing for an adequate empiric antibiotic selection.
The authors present the largest study performed in the United States, comprising 842 VAP patients and 2,243 control subjects. The mean interval between intubation and the identification of VAP was 3.3 ± 6.6 days. A crude incidence of 9.3% was found in ventilated patients. The authors also reported morbidity and economic variables resulting in an increase in mean ICU and hospital stays (6.1 days), mean period of mechanical ventilation (9.6 days), and a mean doubled increase in hospital charges ($41,294). P aeruginosa was isolated most frequently in patients with VAP, occurring > 4 days after the start of mechanical ventilation (19.7%), while S aureus was isolated most frequently in patients in whom VAP was diagnosed before the fourth day of onset of mechanical ventilation (23.7%). They found no attributable mortality at 30 days. An outstanding conclusion is that intermediate underlying illness severity is one of the independent risk factors for developing VAP, as reported previously for late-onset VAP episodes caused by P aeruginosa. The main goal of this study concerned the impact on the design of future studies aimed at VAP prevention.
Top Ten List in Ventilator-Associated Pneumonia (Part 4)
This expert group investigated the potential role of nonpathogenic microorganisms in VAP. Three hundred sixty-nine VAP patients were identified during the study period. Only 29 episodes were considered to have been caused by commensal pathogens. The percentage of pathogens of unknown etiology was not reported. Polymicrobial VAP was found in 77 patients, and these patients were excluded from the study. Most patients had risk factors for more virulent or resistant pathogens like COPD, glucocorticoid therapy, or immunosuppression. Although the onset of 10 cases occurred before the sixth ICU day, all Gram-negative commensal pathogens that were isolated were sensitive to therapy with a third-generation cephalosporin or amoxicillin/clavulanic acid. Seven of 29 patients did not receive adequate treatment, and mortality did not increase significantly. Although the authors attribute a pathogenic role to commensal bacteria, they did not find any difference in mortality rate between patients with or without VAP. In addition, besides the limited relevance to mortality, only 20% of patients who died had received histologic confirmation of a diagnosis of pneumonia. Commensal pathogens can produce fulminant infections in immunocompromised patients, but this is the first study that has suggested the need to treat commensal isolates in patients with VAP. Future investigations are needed to define the pathogenic role of commensal agents in these kinds of patients.
The occurrence of and effect on prognosis of delays in the beginning of the treatment of VAP have not been reported before, to our knowledge. Appropriate initial antibiotic treatment has been reported to reduce in-hospital mortality. Iregui et al have found an increase in the hospital mortality rate with delayed initial treatment. Adequate initial treatment usually has been defined as an antibiotic with in vitro susceptibility to the pathogen isolated in respiratory samples. This definition needs the addition of onset timing in antibiotic administration. The most common cause of inadequate initial treatment was a delay in writing the medical orders. The presence of a resistant organism accounted for < 20% of cases. It is important to note that diagnostic delays were not counted, although radiologic criteria included an infiltrate persistence of > 72 h. Inadequate clinical evaluation and waiting for microbiological results were reasons of delayed empiric treatments.