Hospital Admission For Community-acquired Pneumonia Research Articles

Malnutrition, Functional Decline, and Institutionalization in Older Adults after Hospital Discharge Following Community-Acquired Pneumonia.

Community-acquired pneumonia (CAP) is a major threat to older adults, but mid-term implications are poorly described. The aim was to analyze functional decline, institutionalization, malnutrition, and risk factors after hospital admission for CAP. This prospective observational study included patients over 65 years discharged after CAP between May 2019 and July 2021. We performed a comprehensive geriatric assessment and a general nutritional assessment 30-60 days after CAP. This included the MNA and blood test with trace elements and vitamins. The main outcomes were functional decline, institutionalization, and malnutrition. Multivariate logistic regression was used for the analyses. In total, 144 patients of 77.15 ± 7.91 years, 55.6% male, and 9% previously institutionalized were analyzed. At hospital admission, the Charlson Comorbidity Index (CCI) was 1.5 ± 1.6, the Pneumonia Severity Index was 98.1 ± 25.9, and the previous Barthel Index (BI) was 93.06 ± 17.13. Hospital stay was 9.72 ± 7.88 days. After 44.6 ± 14.4 days, 48.6% patients showed functional decline and 19.4% were institutionalized. Age (OR 1.17; CI 95% 1.09-1.26), previous institutionalization (29.1; 3.7-224.7), BI (1.09; 1.05-1.14), CCI (1.5; 1.1-2.1), and length of stay (1.1, 1.02-1.18) were independently associated with functional decline. The only predictors of new institutionalization were previous BI (0.96; 0.93-0.99) and length of stay (1.06; 1.00-1.13). The MNA indicated malnutrition in 28% of the community-dwelling patients and 67.9% of those institutionalized, with risk of malnutrition being 45.7% and 9.5%, respectively, after an average of 44.6 days of CAP diagnosis. The predictors of malnutrition were previous institutionalization (10.62; 2.20-51.21), BI (0.95; 0.92-0.98), and length of stay (1.12; 1.04-1.20). Micronutrient deficiencies were mainly zinc (61.8%), vitamin D (54.5%), and vitamin C (45.1%). An MNA score < 17 points or hypoalbuminemia showed good specificity to identify these deficiencies. After CAP admission, functional decline, institutionalization, and malnutrition rates were high. Longer hospital stay was a common risk factor for all outcomes. The presence of hypoalbuminemia or an MNA < 17 in older patients should prompt suspicion of deficiencies in micronutrients, such as vitamin D, C, and zinc.

Incidence of community-acquired pneumonia hospitalisation in persons with bronchiectasis during the COVID-19 lockdown in Denmark: a retrospective cohort study

BackgroundPersons with bronchiectasis have a high risk of community-acquired pneumonia. Social distancing measures, implemented to prevent the spreading of SARS-CoV-2, could potentially reduce the incidence of other infectious diseases.Research questionWas...

Readmission following hospital admission for community-acquired pneumonia in England

IntroductionReadmission rates following hospital admission with community-acquired pneumonia (CAP) have increased in the UK over the past decade. The aim of this work was to describe the cohort of patients...

Sex-differences in incidence of hospitalizations and in hospital mortality of community-acquired pneumonia among children in Spain: a population-based study

The aim of this study is to examine trends from 2016 to 2019 in the incidence of hospitalizations and in-hospital mortality (IHM) of subjects < 18 years with community-acquired pneumonia (CAP), assessing possible sex differences. We used Spanish national hospital discharge data to select all patients < 18 years with CAP. We identified 43,511 children (53% boys) hospitalized with CAP. The incidence of CAP was significantly higher in boys than in girls, with an age-adjusted incidence rate ratio of 1.05 (95%CI 1.03–1.07) for boys compared to girls, and rose from 126 per 100,000 children in 2016 to 131 in 2019 (p < 0.0001). There were no sex differences in isolated pathogens, comorbidities, length of hospital stay, or IHM. Variables independently associated with IHM were age 10 to 17 years, congenital heart disease, neurological diseases, and use of invasive mechanical ventilation. Asthma was a protective factor for IHM among girls.Conclusion: The incidence of hospital admissions for CAP was higher among boys than among girls and rose significantly from 2016 to 2019. There were no sex differences in hospital outcomes. Age 10 to 17 years, congenital heart disease, neurological diseases, and use of mechanical ventilation were risk factors for IHM in both sexes, while asthma was a protective factor among girls. No differences were found in IHM over time.What is Known:• Community-acquired pneumonia is one of the most common reasons for hospitalizations among children.• There are few studies that allow to know the evolution of community-acquired pneumonia in children.What is New:• Incidence of hospital admissions for community-acquired pneumonia was higher in boys than girls and it rose significantly from 2016 to 2019.• Age 10 to 17 years, congenital heart disease, neurological diseases and use of mechanical ventilation were risk factors for in-hospital mortality in both sexes.

Rectal bacteriome and virome signatures and clinical outcomes in community-acquired pneumonia: An exploratory study.

Background Bacterial intestinal communities interact with the immune system and may contribute to protection against community-acquired pneumonia (CAP). Intestinal viruses are closely integrated with these bacterial communities, yet the composition and clinical significance of these communities in CAP patients are unknown. The aims of this exploratory study were to characterise the composition of the rectal bacteriome and virome at hospital admission for CAP, and to determine if microbiota signatures correlate with clinical outcomes.Methods We performed a prospective observational cohort study in CAP patients, admitted to a university or community hospital in the Netherlands between October 2016 and July 2018, and controls. Rectal bacteriome and virome composition were characterised using 16S ribosomal RNA gene sequencing and virus discovery next-generation sequencing, respectively. Unsupervised multi-omics factor analysis was used to assess the co-variation of bacterial and viral communities, which served as primary predictor. The clinical outcomes of interest were the time to clinical stability and the length of hospital stay.Findings 64 patients and 38 controls were analysed. Rectal bacterial alpha (p = 0•0015) and beta diversity (r2=0•023, p = 0•004) of CAP patients differed from controls. Bacterial and viral microbiota signatures correlated with the time to clinical stability (hazard ratio 0•43, 95% confidence interval 0•20–0•93, p = 0•032) and the length of hospital stay (hazard ratio 0•37, 95% confidence interval 0•17–0•81, p = 0•012), although only the latter remained significant following p-value adjustment for examining multiple candidate cut-points (p = 0•12 and p = 0•046, respectively).Interpretation This exploratory study provides preliminary evidence that intestinal bacteriome and virome signatures could be linked with clinical outcomes in CAP. Such exploratory data, when validated in independent cohorts, could inform the development of a microbiota-based diagnostic panel used to predict clinical outcomes in CAP.Funding Netherlands Organization for Scientific Research and Netherlands Organization for Health Research and Development.

1514. Mortality and Readmission in Adults during the First Year Following Hospitalization for Community-Acquired Pneumonia in the US

BackgroundIncreasing evidence suggests that the impact of community-acquired pneumonia (CAP) extends beyond discharge from the hospital and the acute phase of illness. We sought to characterize mortality and hospital readmission across the adult age span and spectrum of comorbidities.MethodsA retrospective cohort design and data from Optum’s de-identified Integrated Claims-Clinical dataset (2009-2018) were employed. Study population comprised all adults who, between 1.1.2013 and 12.31.2017, had ≥ 1 acute-care hospitalization for CAP; each qualifying CAP hospitalization separated by ≥ 365 days was included as a unique observation in analyses. Study outcomes included acute-care hospital readmission for any reason and death for any reason. Hospital readmission was ascertained during the 360-day period following discharge from the CAP hospitalization; death was ascertained during the CAP hospitalization as well as during the same 360-day period. Cumulative rates of mortality and readmission were summarized for all patients as well as subgroups defined on age and comorbidity profile (i.e., healthy, at-risk, high-risk).ResultsStudy population totaled 37,006 patients who contributed 38,809 CAP hospitalizations; mean age was 71 years, 51% were female, and 88% had an at-risk (33%) or high-risk (55%) condition. Hospital readmission was 12.5% during the 30-day post-discharge period, and 42.3% during the 360-day post-discharge period. Mortality was 3.5% in hospital, 8.2% from admission to 30 days post-discharge, and 17.7% from admission to 360 days post-discharge. Mortality rates increased with age and severity of comorbidity profile; readmission rates were highest for persons aged 65-74 years and high-risk persons.Rates of readmission and mortality among adults hospitalized for CAP ConclusionAll-cause mortality up to 1 year following hospital admission for CAP was substantial, and was associated with increasing age and worsening comorbidity profile. Both readmission and mortality were greater at all ages in high-risk and at-risk groups compared with their healthy counterparts. Strategies that prevent pneumonia and/or the pathophysiologic changes that follow CAP, especially among individuals with comorbid conditions, have the potential to reduce morbidity and mortality following CAP as well as healthcare costs associated with readmission.Disclosures Reiko Sato, PhD, Pfizer, Inc (Employee, Shareholder) Derek Weycker, PhD, Pfizer Inc. (Consultant, Grant/Research Support, Scientific Research Study Investigator, Research Grant or Support) Melody Shaff, BA, Pfizer, Inc. (Consultant, Grant/Research Support, Scientific Research Study Investigator, Research Grant or Support) Ahuva Hanau, BS, Pfizer, Inc. (Consultant, Grant/Research Support, Scientific Research Study Investigator, Research Grant or Support) Alexander Lonshteyn, PhD, Pfizer, Inc. (Consultant, Grant/Research Support, Scientific Research Study Investigator, Research Grant or Support) Stephen I. Pelton, MD, Merck vaccine (Consultant, Grant/Research Support)Pfizer (Consultant, Grant/Research Support)Sanofi Pasteur (Consultant, Other Financial or Material Support, DSMB)Seqirus Vaccine Ltd. (Consultant)

Validation for using electronic health records to identify community acquired pneumonia hospitalization among people with and without HIV

BackgroundCohort studies identifying the incidence, complications and co-morbidities associated with community acquired pneumonia (CAP) are largely based on administrative datasets and rely on International Classification of Diseases (ICD) codes; however, the reliability of ICD codes for hospital admissions for CAP in people with HIV (PWH) has not been systematically assessed.MethodsWe used data from the Veterans Aging Cohort Study survey sample (N = 6824; 3410 PWH and 3414 uninfected) to validate the use of electronic health records (EHR) data to identify CAP hospitalizations when compared to chart review and to compare the performance in PWH vs. uninfected patients. We used different EHR algorithms that included a broad set of CAP ICD-9 codes, a set restricted to bacterial and viral CAP codes, and algorithms that included pharmacy data and/or other ICD-9 diagnoses frequently associated with CAP. We also compared microbiologic workup and etiologic diagnosis by HIV status among those with CAP.ResultsFive hundred forty-nine patients were identified as having an ICD-9 code compatible with a CAP diagnosis (13% of PWH and 4% of the uninfected, p < 0.01). The EHR algorithm with the best overall positive predictive value (82%) was obtained by using the restricted set of ICD-9 codes (480–487) in primary position or secondary only to selected codes as primary (HIV disease, respiratory failure, sepsis or bacteremia) with the addition of EHR pharmacy data; this algorithm yielded PPVs of 83% in PWH and 73% in uninfected (P = 0.1) groups. Adding aspiration pneumonia (ICD-9 code 507) to any of the ICD-9 code/pharmacy combinations increased the number of cases but decreased the overall PPV. Allowing COPD exacerbation in the primary position improved the PPV among the uninfected group only (to 76%). More PWH than uninfected patients underwent microbiologic evaluation or had respiratory samples submitted.ConclusionsICD-9 code-based algorithms perform similarly to identify CAP in PLWH and uninfected individuals. Adding antimicrobial use data and allowing as primary diagnoses ICD-9 codes frequently used in patients with CAP improved the performance of the algorithms in both groups of patients. The algorithms consistently performed better among PWH.

Platelet Count within the Normal Range at Hospital Admission is Associated with Mortality in Patients with Community-Acquired Pneumonia.

BackgroundApart from their hemostatic role, platelets are immune cells that play a role in fighting infections. The presence of thrombocytopenia and thrombocytosis at hospital admission are predictors of mortality in community-acquired pneumonia patients. We hypothesized that variations in platelet counts within the normal range also may be associated with mortality in these patients.MethodsThe study included all adults in the North and Central Denmark Regions with a first acute hospital admission for community-acquired pneumonia during 2006–2012. We assessed the association between the first platelet count within ± 24 hours of admission (within the normal range of 150 to 400 x 109/L) and 30-day mortality using Cox models. Analyses were adjusted for age, sex, Charlson Comorbidity Index score, hemoglobin level, leukocyte count, and creatinine level at admission.ResultsAmong the 12,905 study patients, 30-day mortality was 12.4%. The mean platelet count upon admission was 250 × 109/L. Compared with the 250–275 × 109/L category, platelet counts of 151–175 were associated with a lower 30-day mortality (adjusted hazard ratio [aHR]: 0.79, 95% confidence interval [CI]: 0.63–0.99), while higher platelet counts were associated with a higher 30-day mortality (351–375 × 109/L, aHR: 1.34, 95% CI: 1.07–1.68; 376–400× 109/L, aHR: 1.21, 95% CI: 0.94–1.56).ConclusionPlatelet counts, even within the normal range, are associated with mortality in adult patients hospitalized for community-acquired pneumonia.

Low Admission Plasma Gelsolin Concentrations Identify Community-acquired Pneumonia Patients at High Risk for Severe Outcomes.

Plasma gelsolin (pGSN) is an abundant circulating protein that neutralizes actin exposed by damaged cells, modulates inflammatory responses, and enhances alveolar macrophage antimicrobial activity. We investigated whether adults with low pGSN at hospital admission for community-acquired pneumonia (CAP) were at high risk for severe outcomes. Admission pGSN concentrations in 455 adults hospitalized with CAP were measured using enzyme-linked immunosorbent assay. Patients were grouped into the following 4 hierarchical, mutually exclusive categories based on maximum clinical severity experienced during their hospitalization: general floor care without intensive care unit (ICU) admission, invasive respiratory or vasopressor support (IRVS), or death; ICU care without IRVS or death; IRVS without death; or death. Admission pGSN concentrations were compared across these discrete outcome categories. Additionally, outcomes among patients in the lowest quartile of pGSN concentration were compared to those in the upper 3 quartiles. Overall, median (interquartile range) pGSN concentration was 38.1 (32.1, 45.7) μg/mL. Patients with more severe outcomes had lower pGSN concentrations (P = .0001); median values were 40.3 μg/mL for floor patients, 36.7 μg/mL for ICU patients, 36.5 μg/mL for patients receiving IRVS, and 25.7 μg/mL for patients who died. Compared to patients with higher pGSN concentrations, patients in the lowest quartile (pGSN ≤ 32.1 μg/mL) more often required IRVS (21.2% vs 11.7%, P = .0114) and died (8.8% vs 0.9%, P < .0001). Among adults hospitalized with CAP, lower pGSN concentrations were associated with more severe clinical outcomes. Future studies are planned to investigate possible therapeutic benefits of recombinant human pGSN in this population.

What is the seasonal distribution of community acquired pneumonia over time? A systematic review

Community-acquired pneumonia (CAP) is a growing public health concern in many developed countries including Australia. CAP account for an estimated two percent of all overnight hospital admissions in Australia. Despite the significant burden on the Australian healthcare system and the high level of morbidity and mortality associated with CAP, there has been a paucity of research on the incidence of disease in this country, particularly in relation to seasonal variation of emergency department presentations and subsequent admission. The following search terms were used: community-acquired AND pneumonia AND/OR seasonal AND season AND/OR variation OR differences. The limits used for the search terms included: "All Adult"; the years 1948 to current or 1948 to week 1 May 2012, (depending on the database); English language; and with full text. The databases searched included MEDLINE, Embase and CINAHL. Distinct seasonal patterns in the occurrence of CAP were observed: 34% of CAP admissions occurred in spring; 18% in autumn; 26% in winter; and 22% in summer (p=0.036). Hospital admissions for CAP were significantly higher in the winter and spring (p=<0.001) and highest in December (20.5%) and January (25.1%). Peak hospitalisations from January through to April were observed. The included studies were conducted in the northern hemisphere where the months December to February relate to winter. International studies have shown an association between seasonal variation and the occurrence of CAP in temperate and subtropical climates. Selected studies had methodological limitations that limit conclusions and applicability to clinical practice. There are no studies in the Australian context. Further epidemiological studies are required to elucidate this important aspect of the epidemiology of CAP.

Accuracy of C-reactive protein, procalcitonin, and mid-regional pro-atrial natriuretic peptide to guide site of care of community-acquired pneumonia

The use at bedside of C-reactive protein (CRP), procalcitonin (PCT) or mid-regional pro-atrial natriuretic peptide (ANP) has been advocated to help management of patients with community-acquired pneumonia (CAP) in emergency medicine. To assess the effectiveness of CRP, PCT, and ANP measures in assisting emergency physicians deciding hospital admission for CAP with low risk of complication. Multicenter, prospective, observational study with blind evaluation. Emergency departments of 12 French hospitals. Five hundred forty-nine consecutive, immunocompetent adult patients with mild CAP. Centralized and blind measure of baseline CRP, PCT, and ANP; sensitivity, specificity, and positive and negative likelihood ratios for determining hospital admission. Gold standard for admission was defined by experts' advice combined with admission requirement or death at 28 days. Optimal threshold values were determined by receiver operating characteristic (ROC) curves, and area under curve (AUC) of the three biomarkers was compared. According to gold standard, 310 (56%) patients required admission and 239 (44%) needed to be discharged. PCT and ANP levels increased with Pneumonia Severity Index risk categories. ANP (AUC 0.76 [95% CI 0.72-0.80]) more accurately predicted admission requirement than did PCT (AUC 0.65 [95% CI 0.61-0.70]) or CRP (AUC 0.59 [95% CI 0.54-0.64]) (both p values <0.01). We determined that 135 pmol/L was a threshold for ANP level to discriminate admission requirement (positive likelihood ratio 7.45 [95% CI 4.22-8.16]). In a selected population of CAP with low risk of complication, a single ANP measurement was more accurate than CRP and PCT to predict appropriate admission. These results should be confirmed by additional studies.

Effectiveness of the pneumococcal polysaccharide vaccine in preventing pneumonia in the elderly

The objective of our study was to evaluate the effectiveness of the 23-valent pneumococcal polysaccharide vaccine (PPV) in preventing hospital admission for community-acquired pneumonia (CAP) in people ≥65 yrs of age. We conducted a matched case-control study in patients with CAP admitted to five Spanish hospitals. Cases were persons aged ≥65 yrs admitted to hospital through the emergency department, who presented a clinical and radiological pattern compatible with pneumonia, assessed using established criteria. We matched each case with three control subjects by sex, age (±5 yrs), date of hospitalisation (±30 days) and underlying disease. The study period was May 1, 2005 to January 31, 2007. The PPV immunisation status of cases and controls was investigated. Adjusted ORs for vaccination were calculated using logistic regression analysis. A total of 489 cases and 1,467 controls were included in the final analysis. The overall adjusted vaccination effectiveness for all patients was 23.6% (95% CI 0.9-41.0). The adjusted vaccination effectiveness for immunosuppressed patients was 21.0% (95% CI -18.7-47.5). Our results suggest that the PPV may potentially reduce hospitalisations for pneumonia in the elderly and supports vaccination programmes in this age group.

Angiotensin-converting enzyme inhibitor use and pneumonia risk in a general population

The aim of the present study was to assess whether the use of angiotensin-converting enzyme (ACE) inhibitors is associated with a decreased risk of hospitalisation for community-acquired pneumonia (CAP) in a general, essentially white population. Data were obtained from the Dutch PHARMO Record Linkage System. Cases were defined as patients with a first hospital admission for CAP. For each case, up to four population controls were matched by age and sex. The study population comprised 1,108 patients with a first hospital admission for CAP and 3,817 matched controls. After adjusting for several confounders, ACE inhibitor use was not associated with a decreased incidence of pneumonia (adjusted odds ratio (OR) 1.12; 95% confidence interval (CI) 0.88-1.43). Additionally, no significant association was observed in patients with diabetes, respiratory diseases, heart failure, or patients with both of the last two conditions. Furthermore, adjustment of treatment effects on pneumonia risk using stratification on balancing score also showed no significant association between ACE inhibitor use and pneumonia risk within the different strata (overall adjusted OR 1.09; 95% CI 0.87-1.36). In contrast with previous findings in Asian populations, the current authors were not able to confirm the beneficial effect of angiotensin-converting enzyme inhibitors on pneumonia risk in a general, essentially white population.

Prior outpatient antibacterial therapy as prognostic factor for mortality in hospitalized pneumonia patients

To assess whether prior outpatient treatment is associated with outcome in patients hospitalized for community-acquired pneumonia (CAP). All patients with a first hospital admission for CAP between 1995 and 2000 were selected. Patients were divided into two groups, one of patients with use of antibacterial agents prior to hospitalization and one of patients treated as inpatient directly. The main outcome measures were duration of hospital stay and in-hospital mortality. The two patient groups comprised 296 and 794 patients, respectively. The median duration of hospital stay was 10 days and was similar for both groups. In patients with respiratory diseases or heart failure, the median duration of hospital stay was 12 and 14 days, respectively. The overall in-hospital mortality was 7.2% and did not largely differ between both groups. In patients with congestive heart failure, the mortality was 9.8% for controls and 23.3% for patients hospitalized after initial outpatient treatment (adjusted OR 2.78, 95% CI 1.01-7.81). Prior outpatient antibacterial therapy is not associated with outcome in hospitalized pneumonia patients. In patients with underlying chronic heart failure, prior outpatient antibiotic is associated with a significant increased mortality.

Variation in management of community-acquired pneumonia requiring admission to Alberta, Canada hospitals.

Previous studies have shown small area variation in the rate of admission to hospital for patients with community-acquired pneumonia. We determined the rates of admission and length of stay for patients with community-acquired pneumonia in Alberta and the factors influencing admission rates and length of stay. Using hospital abstracts, hospital admissions for community-acquired pneumonia from 1 April 1994 to 31 March 1999 were compared. We classified Alberta hospitals according to geographical regions, by the number of beds, and by number of community-acquired pneumonia cases. There were 12,000 annual hospital discharges for community-acquired pneumonia costing over $40 million per year. The overall in-hospital mortality rate was 12% and the 1 year mortality rate was 26%. Compared with rural hospitals, regional and metropolitan hospitals admitted patients with greater severity of illness as demonstrated by greater in-hospital mortality, cost per case and comorbidity. Age-sex adjusted hospital discharge rates were significantly below the provincial average in both urban regions. Hospital discharge rates for residents in all rural regions and 4 of 5 regions with a regional hospital were significantly higher than the provincial average. After adjusting for comorbidity, the relative risk for a longer length of stay was 22% greater in regional hospitals and about 30% greater in urban hospitals compared to rural hospitals. Seasonal variation in the admission rate was evident, with higher rates in the winter of each year. We conclude that rural hospitals would be likely to benefit from a protocol to help with the admission decision and urban hospitals from a programme to reduce length of stay.

Hospitalized community-acquired pneumonia in the elderly: age- and sex-related patterns of care and outcome in the United States.

Community-acquired pneumonia (CAP) is a frequent cause of hospital admission and death among elderly patients, but there is little information on age- and sex-specific incidence, patterns of care (intensive care unit admission and mechanical ventilation), resource use (length of stay and hospital costs), and outcome (mortality). We conducted an observational cohort study of all Medicare recipients, aged 65 years or older, hospitalized in nonfederal U.S. hospitals in 1997, who met ICD-9-CM-based criteria for CAP. We identified 623,718 hospital admissions for CAP (18.3 per 1,000 population > or = 65 years), of which 26,476 (4.3%) were from nursing homes and of which 66,045 (10.6%) died. The incidence rose five-fold and mortality doubled as age increased from 65-69 to older than 90 years. Men had a higher mortality, both unadjusted (odds ratio [OR]: 1.21 [95% CI: 1.19-1.23]) and adjusted for age, location before admission, underlying comorbidity, and microbiologic etiology (OR: 1.15 [95% CI: 1.13-1.17]). Mean hospital length of stay and costs per hospital admission were 7.6 days and $6,949. For those admitted to the intensive care unit (22.4%) and for those receiving mechanical ventilation (7.2%), mean length of stay and costs were 11.3 days and $14,294, and 15.7 days and $23,961, respectively. Overall hospital costs were $4.4 billion (6.3% of the expenditure in the elderly for acute hospital care), of which $2.1 billion was incurred by cases managed in intensive care units. We conclude that in the hospitalized elderly, CAP is a common and frequently fatal disease that often requires intensive care unit admission and mechanical ventilation and consumes considerable health care resources. The sex differences are of concern and require further investigation.

Seasonal variation in hospital admissions for community-acquired pneumonia: a 5-year study.

We conducted a retrospective analysis of computerized hospitalization and regional meteorological and geophysical data in a university hospital in southern Israel. The aim of the study was to determine and depict the seasonal variation in hospitalization for community-acquired pneumonia (CAP-H) and the factors affecting it, for all age groups combined and by age group, over a 5-year period. All cases of CAP-H over the period from January 1, 1990 to December 31, 1994 were studied by season of the year and age group. The rates of CAP-H for the four seasons were compared by t-tests. Mathematical models based on quasi-Fourier generalized linear models were developed and used to evaluate potential variables and their relative contributions to CAP-H. A total of 4101 CAP-H were analysed in the study. Throughout the study period the prevalence of CAP-H was significantly higher in the winter and spring than in the summer and fall for all age groups combined and within each age group (P<0.00001). When CAP-H was compared between the winter and the spring, we found that in the 0-16 age group CAP-H was higher in the winter (P<.0.00001), in the 17-64 age group it was higher in the spring (P<0.002), and in the 65+ age group as well as for all age groups combined there were no significant differences between these two seasons. The most important factor explaining the variance in CAP-H in the 0-16 age group were direct and indirect effects of minimum daily temperature (31%), in the 17-64 age group direct and indirect effects of the difference between minimum and maximum daily temperatures (19%), and in the 65+ age group it was geophysical factors (13%). There is a significant seasonal variation in CAP-H with higher rates for all age groups in the winter and spring. The extent to which the prevalence of CAP-H is dominant in the winter and spring seasons differs among the age groups, as does the principal variable explaining these differences. The most important factor is the direct and indirect effects of meteorological variables in the 0-16 and 17-64 age groups, and a geophysical one among the more elderly patients.