Incidence rates of pneumonia
There were 443 QRESEARCH practices included in the analysis. Overall there were 34 098 incident cases of pneumonia arising from 29 605 328 patient-years, giving an overall incidence rate of 115 per 100 000 patient-years.
The incidence of pneumonia varied by year and age group, approximately doubling between 1996 and 2005 in all age groups and reaching an age–sex-standardised rate of 150 cases per 100 000 in 2005. The incidence rate was highest in patients aged ≥75 years, next highest in patients aged 0–4 years, and lowest in patients aged 15–44 years. Of all the cases of pneumonia, 25% had lobar or pneumococcal pneumonia. The distribution of specific diagnoses in all cases with pneumonia is presented in . There were 17 172 cases with at least 5 years of prior data, and these were included in the remaining analyses. Of these 4485 (26%) had lobar or pneumococcal pneumonia.
Distribution of diagnoses with the pneumonia outcome.
Baseline characteristics of pneumonia cases and controls
shows baseline characteristics for cases with pneumonia and their matched controls. Cases and controls were well balanced with respect to the length of longitudinal records available prior to the index date. Smoking was more common among cases than controls, and there was a slight tendency for cases to be from more deprived areas than controls. Uptake of influenza vaccination in the preceding 12 months was also marginally higher in cases than controls.
Characteristics of cases with pneumonia and age–sex–practice–calendar year-matched controls.
Risks of pneumonia according to disease risk groups
and show the number of cases and controls with diagnoses for diseases in the established risk groups, and in the potential new risk groups prior to the date of diagnosis of pneumonia in cases, and to the equivalent index date in controls. Almost half of the cases (46%) had been diagnosed with at least one of the diseases in the existing risk groups, compared to 29% of the controls. The unadjusted ORs for all of the current risk factor diseases were >1.5, apart from in the immunosuppressed patient group, where the unadjusted OR was 1.12 (95% CI = 1.03 to 1.21).
Risk of pneumonia in patients of all ages.
Characteristics of cases and matched controls and odds ratios for pneumonia for diseases currently and potentially considered as risk factors for pneumococcal disease, all patients.
For the new potential risk factors, the proportion of cases diagnosed with any of these diseases was significantly higher than among controls. Most of the unadjusted OR were >1.5. Among the cancer patients, those with lung cancer had the highest unadjusted OR for pneumonia (unadjusted OR: 4.73, 95% CI = 3.58 to 6.25). Multiple sclerosis showed the next highest risk of pneumonia (unadjusted OR: 3.20, 95% CI = 2.40 to 4.26). As the unadjusted OR for osteoarthritis was only 1.12 (95% CI = 1.06 to 1.18), it was excluded from further analysis. More than one-fifth of cases (21.2%) had been diagnosed with at least one of the potential risk factors (stroke or transient ischaemic attack [TIA], rheumatoid arthritis, Parkinson's disease, multiple sclerosis, dementia, osteoporosis, or any type of cancer) compared with 12.6% of controls.
Adjustment for a number of potential confounding variables tended to reduce the OR, with the exception of the immunosuppressed, multiple sclerosis, and dementia groups. The adjusted ORs for all current and potential risk groups were greater than 1.5, except for in the diabetes, immunosuppressed, and any cancer groups. The highest adjusted ORs were for multiple sclerosis, HIV/AIDS, and asplenia.
shows the numbers of patients diagnosed with only a current risk group disease, only a new potential risk group disease, and with diseases from both risk groups. Out of 7894 cases diagnosed with a current risk group disease, 2696 patients (34%) were also diagnosed with at least one of the new potential risk group diseases, and out of 20 985 controls with a current risk group disease, 5957 (28%) also had a new risk group disease. For example, most of the cancer patients (97.6% of cases with cancer and 97.0% of controls) fall into the immunosuppressed group. The adjusted risk of pneumonia in patients with one or more current risk factor conditions but no new risk factors was 2.3-fold increased (OR: 2.33, 95% CI = 2.23 to 2.44) compared with patients with no current or new risk factors. In patients with one or more new potential risk factor conditions (excluding osteoarthritis) and not diagnosed with diseases from the current risk group, the risk was almost 2.5-fold increased (OR: 2.44, 95% CI = 2.24 to 2.65) after adjusting for smoking, deprivation, use of influenza vaccine, use of pneumococcal vaccine, and years of medical records.
Online Table 4
Characteristics of cases and matched controls and odds ratios for pneumonia for a number of diseases currently and potentially considered as risk factors for pneumococcal disease, all patients and patients aged 5–64 years.
also show how multiple conditions affect the risk of pneumonia: patients with three or more conditions have a risk almost three times as high as patients with only one condition.
The analyses were repeated on patients aged 5–64 years. The results were similar to those in patients of all ages. The risk of pneumonia in those with one or more current risk factor diseases and no new risk factor disease adjusted for the confounding variables was twofold increased (OR: 1.96, 95% CI = 1.82 to 2.11), and in those with one or more diseases from the potential risk factor list (excluding osteoarthritis) and not diagnosed with any of the current risk group diseases, it was 2.3-fold increased (OR: 2.32, 95% CI = 1.91 to 2.82). These results are shown in and .
Risk of pneumonia in patients aged 5–64 years.
The analyses also showed similar results to the analyses performed for the whole sample when restricted to: patients aged ≥65 years; patients with pneumonia diagnosed before 2003; and patients with lobar or pneumococcal pneumonia. The increased risk of pneumonia for those patients with at least one of the diseases from the current risk factor list was approximately the same (OR ranged from 2.29 for patients with lobar pneumonia to 2.32 for patients with pneumonia diagnosed before 2003). The increased risk of pneumonia for patients with at least one disease from the new potential risk factor list and without diseases from the current risk factor group varied slightly (OR ranged from 1.94 for patients with lobar pneumonia to 2.50 for patients aged ≥65 years and patients diagnosed before 2003).
shows the number of cases and controls vaccinated with pneumococcal vaccine. Only 16.4% of cases and 14.4% of controls had records of pneumococcal vaccination in the last 5 years. Among the patients with at least 10 years of medical records, the proportion of cases who had been vaccinated in the last 10 years was 18.3%, and the proportion of controls was 14.3%. shows results from adjusted analyses for time since the last vaccination in individuals with at least 5 and 10 years of data. There was a significantly lower risk of pneumonia in patients who had been vaccinated between 15 and 365 days previously, compared with those not vaccinated in the last 5 years (OR 0.83, 95% CI = 0.76 to 0.92), but not in patients vaccinated more than 12 months earlier.
Timing of pneumococcal vaccination for all pneumonia cases and for cases with lobar or pneumococcal pneumonia and their matched controls.
also shows the results of the analysis regarding the use of pneumococcal vaccine, but restricted to patients with lobar or pneumococcal pneumonia. The adjusted OR were similar to those for all pneumonia cases, although they were not statistically significant at the 1% significance level.
All the analyses were performed assuming missing smoking status for children aged <15 years as non-smokers. Exactly the same results were obtained for all analyses, assuming smoking status for children as not recorded.