Introduction

Pneumonia represents one of the most frequent and severe infectious complications in hospitalized patients [1], with an estimated prevalence of 4-6% [2,3] and associated with high morbidity and mortality. Although community-acquired pneumonia (CAP) requiring hospitalization is widely studied and recognized, nosocomial pneumonia, especially non-ventilator hospital-acquired pneumonia (NV-HAP), poses a significant diagnostic and epidemiological burden [4]. Few studies evaluate the workload and global characteristics of patients with pneumonia of any origin in hospitalized patients, their etiologies, and the opportunities for intervention with diagnostic and/or therapeutic advice. Moreover, a limited number of prospective studies have applied homogeneous methodologies and comparable definitions of pneumonia [2,3], which hinders direct comparison across series. Most available data focus on specific subgroups of patients rather than on the overall prevalence of pneumonia among hospitalized adults [5-8]. The prevalence of NV-HAP is particularly poorly understood, as is the proportion it represents among pneumonias of other origins. The availability of baseline data would allow an appropriate assessment of advisory interventions for these patients and their real impact. Clinical practice guidelines do not propose systematic follow-up models for hospitalized patients with any form of pneumonia, nor indications to intervene with telematic advice to responsible physicians. Monitoring could help to optimize resources and adjust preventive protocols [9], with particular benefit in immunocompromised patients [10], individuals with cardiopulmonary diseases [11], those admitted for acute respiratory infections [9,12], or those undergoing invasive procedures [13,14]. The primary objective of the present study is to determine the prevalence of pneumonia in adult patients hospitalized in a 1,200-bed institution. Secondary objectives include identifying deviations in clinical management with opportunities for advice to improve diagnosis and treatment.

Materials and methods

This descriptive cross-sectional study, focused on the prevalence of pneumonias, was conducted in a tertiary general hospital with a total capacity of 1,204 beds. The study population included all patients over 18 years of age admitted to the institution during the defined research period, encompassing both immunocompetent and immunocompromised individuals. A single investigator, a postdoctoral associate physician specialized in infectious diseases, carried out the prevalence cross-section through a rapid and systematic telematic review of the records of all admitted adult patients. The prevalence survey was conducted on a single cross-section, completed over 12 non-consecutive days during July 2025, following the European Centre for Disease Prevention and Control (ECDC) surveillance study recommendations [15]. A total of 300 vacant beds corresponding to seasonal ward closures during the summer months, as well as 163 beds allocated to pediatric patients and 88 beds located in a center specializing in chronic rehabilitation admission, were excluded from the analysis. After these exclusions, from a total of 1,204 institutional beds, 653 adult acute-care beds were finally analyzed. Data were collected electronically using a basic form (Data Set 1), recording essential demographic and clinical information. We included all patients with active pneumonia using the following criteria: radiologic infiltrate compatible with pneumonia, not explained by another cause, plus at least one of the following clinical features: fever, leukocytosis or leukopenia, or purulent sputum, dyspnea, respiratory failure, pleuritic chest pain, or crackles. Episodes of pneumonia that had already resolved and did not require any further antibiotic therapy at the time of enrollment were excluded. In patients with active pneumonia at the time of the study, a second set of variables was applied to classify cases as community-acquired pneumonia (CAP), ventilator-associated pneumonia (VAP), or non-ventilator hospital-acquired pneumonia (NV-HAP). According to the latest guidelines, CAP includes pneumonia criteria present within the first 48 hours of admission. VAP is defined as episodes arising after 48 hours of mechanical ventilation (MV) initiation or as pneumonia appearing within 48 hours after extubation [16]. NV-HAP is defined as pneumonia occurring at least 48 hours after admission [4, 17-20]. In patients receiving MV, episodes occurring within the first 48 hours after MV initiation are classified as CAP if MV starts within the first 48 hours of admission or as NV-HAP if MV starts after 48 hours of admission [21]. All patients with a diagnosis of pneumonia underwent a third evaluation of the records (third data set) that included a detailed analysis of the diagnostic criteria used, the attempts to determine the etiologic agent, and microbiological analysis in cases where a specific cause was identified. To assign an overall evaluation to each patient and identify potential areas for improvement, we designed diagnostic and therapeutic quality scales specifically for this study, based on the main international clinical guidelines for pneumonia [4,18,19, 22, 23]. Each scale consisted of five items scored from 0 to 2 points, yielding a total score from 0 to 10, with higher values indicating better adherence to evidence-based clinical standards. The items included in each scale are detailed in Table 1. 

Finally, a prospective follow-up of the dynamic cohort of all pneumonia patients was conducted to analyze clinical evolution, complications, length of stay, and 30‑day mortality from enrollment. These variables were collected prospectively, with data gathered 30 days after the initial classification and assessment of each case. In addition, the mean hospitalization cost per episode was calculated, broadly estimating an average cost of €700 per day per patient in the acute wards and €2,500 per day in the intensive care units (ICU). Statistical analysis. Quantitative data were presented as medians with absolute ranges or interquartile ranges (Q1-Q3). Qualitative variables were summarized using absolute and relative frequencies, along with 95% confidence intervals (CI).

Results

Overall prevalence and clinical characteristics. During a 12-working-day period in July 2025, a single investigator reviewed a total of 653 adult inpatients at the institution. Of these, 24 patients met the diagnostic criteria for pneumonia, representing a prevalence of 36.8 per 1,000 survey beds. The median age in this group was 67.4 years (95% CI 57 - 87.4). Table 2 details the clinical characteristics of patients with pneumonia and their distribution by reason and admission service. Most pneumonia cases occurred in patients hospitalized in medical wards (66.7%), with 41.7% occurring in the internal medicine service.  Radiologic and clinical criteria observed in pneumonia cases are specified in Table 3. The majority of cases (62.5%) were identified by a single posteroanterior (PA) projection on chest radiography, with 16.7% showing radiologic complications such as effusion or cavitation. Clinically, the most frequent sign was respiratory failure, present in 79.2% of patients. Microbiological sampling was attempted via respiratory cultures in 54.2%, blood cultures in 75%, antigen testing in 62.5%, and PCR for respiratory viruses in 83.3%. Microbiological confirmation was obtained in 29.2% of all pneumonias (Table 4). The most frequent microorganisms were methicillin-susceptible Staphylococcus aureus (MSSA) in respiratory samples (n=2) and coronavirus detected by PCR (n=2) (Table 4). Assessment of a possible intervention. A quantitative assessment of the quality of diagnosis and treatment was performed on a 1-10 scale for each pneumonia case (Table 4). The median diagnostic value was 8 (IQR 6.8-9), and the therapeutic value was 7.5 (IQR 6.8-8). Specifically, in empirical treatment, antibiotic therapy could have been stopped days earlier in 83.3% of all cases, and antimicrobial coverage could have been reduced in 37.5% of cases. Globally, 100% of patients had a diagnostic and/or therapeutic score below 10, indicating room for improvement in at least one of these areas. Prognosis. Table 5 presents clinical evolution and 30-day prognosis in the selected cohort of all pneumonia patients. Mortality was 16.7%, with a median hospital stay of 12 days and an estimated cost of €13,200 per admission. In addition, six cases of pneumonia (25%) with the development of complications during the episode were observed prospectively: parapneumonic effusion (n = 2), hemothorax (n = 1), necrotizing pneumonia (n = 1), abscess formation (n=1), and catheter-associated bacteremia (n = 1). NV-HAP results. Of all hospitalized pneumonias, 25% (n = 6) were NV-HAP, with a median age of 74.1 years (IQR 70.8-83.2) and a median Charlson index of 8.5 (IQR 6.5-9). The NV-HAP prevalence relative to total hospitalized patients was 9.2 per 1,000 patients (n=6) (Table 2). Clinically, 66.7% remained afebrile during the episode, and 83.3% had respiratory failure. Of NV-HAP patients, 83.3% had an alternative or concomitant diagnosis of heart failure. Analytically, 50% had leukocytosis and elevated C-reactive protein (CRP), and 16.7% had an elevated procalcitonin in the first 3 days of the episode (Table 3). In this group, blood cultures were requested in 50% of cases and respiratory samples in 33.3%, with negative results in all cases. SARS-CoV-2 was identified as the etiologic agent in one case by PCR (Table 3). NV-HAP had the lowest diagnostic assessment compared with other pneumonias, with a median of 7 (IC 6-8.8). Potential areas for improvement were identified in all patients, both in diagnostic and therapeutic areas. Regarding treatment, 66.7% could have been advised to provide fewer days of antibiotic therapy, and in 16.7% antibiotic coverage could have been reduced (Table 4). Regarding prognosis, this group had the longest admissions on the non-ICU ward compared with other pneumonias, with a median hospital stay of 24.5 days and an estimated cost of €17,150 per episode (Table 5).

Discussion

Our study indicates that it is possible to conduct with limited resources surveillance of the total burden that hospitalized patients with pneumonia represent within an institution. In our case, 37/1,000 hospitalized patients had pneumonia, and on the day of the study, 100% of pneumonia patients would have benefited from diagnostic or therapeutic advice. Our study, performed by a single person over 12 days, showed operability under limited conditions and the possibility of being repeated biannually to reduce seasonal bias. 

The seriousness of hospitalized pneumonia is undisputed, with reported in-hospital mortality ranging from 7% to 22% [2, 24, 25]. Nevertheless, information on the total burden of pneumonia in hospitalized patients remains partial or fragmented in studies in which the type [6], age [7], or comorbidity [8] are selected as central issues. Regarding the global burden of pneumonias, a retrospective US study (2001-2014) reported a prevalence of approximately 4.4% at the national level [2] and 6.2% in New York City [3], figures similar to those observed in our study (36.8/1,000). However, data on hospitalized pneumonia remain limited, particularly in Europe, where comparable series are scarce. The available American studies [2,3] were based on retrospective continuous surveillance using administrative discharge databases. Their reliance on coded diagnoses may have led to inaccurate estimation of pneumonia cases and underrepresentation of nosocomial subtypes. Differences in case definitions, hospital settings, and observation periods likely explain the variability in reported rates.

In contrast, our point-prevalence design, based on direct clinical record review, provides validated data and a more accurate assessment of diagnostic and therapeutic practices. We are aware that our study was performed in a month (July) with fewer cases of patients hospitalized with pneumonia [26-29], and, in our opinion, studies like ours could be performed with semiannual intervals to evaluate seasonal variations and address the efficacy of interventions [30-34]. While only severity indices that measure mortality or severity are used for the management of pneumonias [35-38], we did not find validated tools recommended to assess diagnostic accuracy or therapeutic approaches in hospital pneumonia as provided by clinical guidelines [4,18,39]. We propose a bespoke quality index to assess diagnostic and therapeutic interventions. In 100% of analyzed cases, opportunities to optimize diagnosis or treatment were identified: in 83.3% antibiotics could have been shortened, and in 37.5% antibiotic coverage could have been reduced, which would have improved resource efficiency [30]. Although 25% of patients had local complications, treatment duration was assessed considering the required duration for each complication, making it unlikely that these complications biased the evaluation of overall treatment duration.

These findings have relevant clinical implications. Implementing structured diagnostic and therapeutic assessment tools in routine practice could help promote timely microbiological testing, more appropriate antibiotic selection, and shorter treatment durations, thereby supporting antimicrobial stewardship initiatives. Such evaluations could also facilitate targeted interventions within hospital infection control initiatives. Scientific societies support periodic surveillance of hospital infections through systems that enable rapid, coordinated interventions between infection control staff and the clinical team [15,30], with demonstrated benefit and cost-effectiveness [31-34], especially in critically ill and immunocompromised patients [10,40]. For example, influenza surveillance in hospitalized patients during viral seasons can reduce nosocomial infection rates from 17% to 9% and shorten hospital stays [41]. However, we don’t know of any proposals specifically applied to patients hospitalized with pneumonia. Of particular concern, in our opinion, are the patients with NV-HAP, who represent the most common form of hospital-acquired pneumonias.

This group had the longest hospital stay outside the ICU and would particularly benefit from diagnostic and therapeutic advice, given its higher severity and poorer diagnosis. Limitations of the study include seasonality, which would need to be addressed with a second study, and the fact that it was conducted at a single center. This may have affected the number of cases recorded, limiting extrapolation to other times of the year. Although a total sample of 600 hospitalized patients was analyzed, the number of pneumonia cases detected is not large enough to perform formal statistical significance testing. However, these limitations do not prevent the study from achieving our primary objective: to evaluate the feasibility of surveillance in a descriptive, objective, and guideline-consistent way of the magnitude of pneumonia in a general hospital during a summer month and to assess the potential for an intervention.

In the future, it is important to assess the feasibility of performing this procedure continuously in institutions capable of clinical interventions, or at least twice a year if continuous assessment is not possible. Our model has proven feasible and, with relative ease, has provided the dimension of the problem and the opportunities for intervention within it. We intend to repeat the same study during the winter months and subsequently evaluate the effectiveness of a rapid interventional counseling system. 

Conclusion

This study reveals that there is a substantial burden of pneumonia in a tertiary-care hospital. An etiological agent could be identified in less than one-third of episodes, highlighting the limited yield of microbiological testing. Diagnostic and therapeutic evaluations revealed that all patients presented opportunities for improvement, mainly regarding the duration and spectrum of antibiotic therapy.

These findings support the feasibility of rapid single-observer surveillance in a tertiary hospital and its potential value for designing targeted interventions to optimize pneumonia diagnosis and treatment. 

Funding

This study was funded by Instituto de Investigación Sanitaria Gregorio Marañón (IiSGM).

Author contributions

Conceptualization, M.F, E.B, and P.M.; methodology, M.F, E.B, A.B, A.G, A.A-U and P.M.; software, M.F, E.M and A.B.; validation, M.F, E.B, A.B, A.G, A.A-U and P.M.; writing and original draft preparation, M.F, E.B, and P.M; review and editing, M.F, E.B, A.B, A.G, A.A-U and P.M; supervision, E.B and P.M. All authors have read and agreed to the published version of the manuscript.

Conflict of interest

The authors declare no conflicts of interest regarding this manuscript.

AI statement

No artificial intelligence tools were used in the writing, analysis, interpretation, or review of this article.

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