Abstract
BACKGROUND:
Community-acquired pneumonia (CAP) caused by Escherichia coli (E. coli) is uncommon, and its clinical features and prognosis remain insufficiently characterized.
OBJECTIVES:
To compare the clinical, laboratory, radiological, and prognostic characteristics of community-acquired E. coli pneumonia (CAECP) with CAP caused by other pathogens.
DESIGN:
Single-center retrospective observational cohort study
SETTINGS:
Department of Pulmonology, Kocaeli City Hospital, İzmit, Kocaeli, Türkiye from April 2023 to March 2025.
PATIENTS AND METHODS:
Adult patients hospitalized with CAP and positive sputum cultures were reviewed. Hospital-acquired and ventilator-associated pneumonias were excluded. Patients were classified as CAECP or Other-CAP. Demographic, clinical, laboratory, radiological, CURB-65, Pneumonia Severity Index (PSI), and outcome data were compared. A targeted multivariable logistic regression model adjusted for age and malignancy evaluated 90-day mortality.
MAIN OUTCOME MEASURES:
In-hospital mortality, 90-day mortality, intensive care unit admission, and hospital length of stay.
SAMPLE SIZE:
Sixty-eight patients (37 CAECP, 31 Other-CAP)
RESULTS:
Median age (69 [interquartile range, IQR 50.7–71] vs 67 [56–70] years; P=.805), sex distribution (P=.452), comorbidity burden (P=.094), body temperature (P=.970), heart rate (P=.592), C-reactive protein (P=.731), procalcitonin (P=.749), multilobar involvement (P=.246), and air bronchogram (P=.938) were comparable between groups. Mean CURB-65 (1.73±0.90 vs 1.45±0.99; P=.253) and PSI (108.6±40.6 vs 95.4±27.6; P=.143) were also similar. Hospital stay was significantly longer in CAECP (15.7±15.5 vs 9.6±7.0) days; P=.047). In-hospital mortality was numerically higher (14% vs 0; P=.058), while 90-day mortality was significantly higher (49% vs 16%; P=.005). After adjustment for age and malignancy, CAECP remained independently associated with 90-day mortality (aOR, 7.41; 95% CI, 1.85–29.71; P=.005).
CONCLUSION:
CAECP resembles other CAP etiologies at presentation, but is associated with longer hospitalization and markedly higher 90-day mortality despite similar baseline severity scores.
LIMITATIONS:
Single-center retrospective design, small sample size, and limited number of mortality events.
Keywords: Escherichia coli, community-acquired pneumonia, mortality, prognosis
INTRODUCTION
Community-acquired pneumonia (CAP) remains one of the leading causes of morbidity and mortality both in our country and globally. Although the frequency order of CAP pathogens varies according to different countries and regions, the most common bacterial etiologic agents include Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Mycoplasma pneumoniae, and Chlamydophila pneumoniae. While Gram-positive bacteria are the primary cause of most CAP cases, Gram-negative bacteria are generally associated with hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP).1,2 Escherichia coli (E. coli) is a Gram-negative, facultatively anaerobic, motile, non-spore-forming, and lactose-fermenting bacillus belonging to the Enterobacteriaceae family.3 Although E. coli is a normal inhabitant of the human intestinal tract, pathogenic strains are important causes of a wide spectrum of extraintestinal infections, particularly in urinary tract and bloodstream, while also being implicated in meningitis, intra-abdominal and various other invasive infections. In contrast, E. coli is not usually regarded as a major cause of pneumonia.4 Rather, it is considered a less common, non-core respiratory pathogen encountered predominantly in patients with specific predisposing factors, such as advanced age, chronic comorbidities, impaired functional status, recent hospitalization, antibiotic exposure, aspiration risk, and healthcare-associated contact. These conditions may facilitate colonization of the oropharyngeal and respiratory tract by Enterobacterales and increase the likelihood of subsequent lower respiratory tract infection.5
Although rare as a cause of CAP, E. coli pneumonia (ECP) is frequently encountered among HAP and VAP pathogens and is associated with substantially higher mortality rates than other pneumonias. Research indicates that the mortality rate of Gram-negative bacterial pneumonia remains significant even if optimal antibiotic therapy is administered.6 Various studies have demonstrated that ECP has a poorer clinical course than other pneumonias.2,7 CAP treatments are almost always initiated empirically, and E. coli is not among the primary agents considered in the etiology of CAP. Whether the clinical, radiological, and prognostic characteristics of community-acquired ECP (CAECP) should be evaluated similarly to general CAP or differently will be clarified in focused clinical studies. This study aimed to differentiate the clinical, radiological, and prognostic characteristics of CAECP among general CAP cases hospitalized in a tertiary care pulmonology department.
PATIENTS AND METHODS
Study design and ethical approval
The present study is a single-center, retrospective, observational cohort performed in accordance with the Declaration of Helsinki. Approval was obtained from the local ethics committee (Decision No: 2023-133, Date: 27.11.2023). Adult patients admitted to our pulmonology department with a diagnosis of CAP between April 2023 and March 2025 who had positive culture growths from lower respiratory tract specimens (sputum cultures) were included. Non-CAP pneumonias (HAP and VAP) and other respiratory infections (e.g., bronchiectasis exacerbations, tracheobronchitis) were excluded. Patient medical records were reviewed retrospectively, and clinical, demographic, laboratory, radiological, and treatment characteristics were recorded.
CAP diagnostic and treatment protocol
In our clinic, the CAP diagnostic algorithm, empirical treatment selection, and patient monitoring are conducted in accordance with national guidelines adapted for Türkiye while adhering to the fundamental principles of international CAP management guidelines.8,9 Patients are diagnosed based on the presence of appropriate clinical symptoms, physical examination findings, and pulmonary infiltrates observed on chest radiographs or computed tomography (CT). Following diagnosis, microbiological sampling is performed to identify the responsible microorganism, and empirical antibiotic therapy is initiated concurrently.
Preferably, the first sputum sample taken in the morning is sent to the microbiology laboratory. To understand whether the sputum sample is contaminated by the upper respiratory tract, the sample is examined using the Gram staining method. Samples with a total score greater than 0 according to the Bartlett scoring method are taken for culture. The samples are cultured on sheep blood agar, chocolate agar, and eosin blue agar, and incubated for 18–24 hours at 35°C in an environment with 5–10% CO2. Cultures were evaluated using routine qualitative microbiological methods; no quantitative colony-count threshold was applied.10 The isolation of E. coli was interpreted in conjunction with the clinical and radiological diagnosis of CAP rather than on culture positivity alone.
CURB-65 is a five-item clinical severity score comprising confusion, serum urea >7 mmol/L, respiratory rate ≥30/min, low blood pressure (systolic <90 mmHg or diastolic ≤60 mmHg), and age ≥65 years, and is used to stratify mortality risk and guide management in patients with community-acquired pneumonia.11 The Pneumonia Severity Index (PSI) is a validated clinical prediction rule based on demographic, comorbidity, physical examination, laboratory, and radiographic variables, and is used to stratify 30-day mortality risk in patients with community-acquired pneumonia.12 PSI and CURB-65 are widely used and validated prognostic scoring systems for assessing disease severity and estimating mortality risk in patients with pneumonia. Hospitalization is indicated for patients meeting any of the following criteria: CURB-65 score >2, PSI score >91, rapidly progressive pneumonia, oxygen saturation <92%, or presence of severe complications such as oral intake failure, treatment non-compliance, substance abuse, psychiatric illness, cognitive or functional impairment, or poor social support.
Potential antibiotic resistance risk factors are routinely evaluated. Hospitalization or antibiotic use within the previous 3 months, or isolation of a resistant bacterium from a respiratory sample within the previous year, are considered risk factors for resistant microorganisms. For patients without resistance risk factors, initial empiric therapy consists of a non-pseudomonal thirdgeneration cephalosporin combined with a macrolide, a beta-lactam/beta-lactamase inhibitor combined with a macrolide, or respiratory fluoroquinolone monotherapy. For patients with resistance risk factors, anti-pseudomonal antibiotic regimens are preferred.
Evaluation of demographic, clinical, laboratory, and radiological features
Demographic characteristics such as age, gender, presence of comorbid conditions, and duration of hospital stay were recorded. Clinical parameters including fever, heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), and peripheral oxygen saturation measured via pulse oximetry at the time of admission were documented. Routine laboratory parameters evaluated at presentation included white blood cell (WBC) count, hemoglobin (HGB), platelet count (PLT), serum C-reactive protein (CRP), procalcitonin (PRC), lactate dehydrogenase (LDH), urea, creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and albumin levels. When available, admission thoracic computed tomography (CT) scans were analyzed for specific radiological patterns, including lobar or multilobar involvement, number of involved segments, ground-glass opacities, air bronchograms, consolidation, and pleural effusion.
Prognostic assessment and outcome measures
To evaluate baseline disease severity and prognostic status, CURB-65 scores (Supplementary Table 1)11 and PSI scores (Supplementary Table 2) developed by Fine et al12 were calculated at the time of hospital admission. Outcome parameters, including total hospital length of stay, treatment success (discharge), transfer to the intensive care unit (ICU), in-hospital mortality, and 90-day mortality, were analyzed. Subjects were divided into two comparative study groups: patients with cultureproven E. coli growth (CAECP group) and patients with culture-proven growth of any other typical CAP pathogen (Other-CAP group).
Statistical analysis
Statistical analyses were performed using IBM SPSS for Windows, Version 24.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics for continuous variables were presented as mean±standard deviation (SD) for normally distributed data, or as median (interquartile range [IQR]) for non-normally distributed data. Categorical variables were expressed as frequencies (n) and percentages (%). The normality of data distribution was assessed using the Kolmogorov-Smirnov test. Comparisons between groups were performed using the Chi-square test or Fisher's exact test for categorical variables, and the independent samples t-test or Mann-Whitney U test for continuous variables, as appropriate. A two-sided P value of less than .05 was considered statistically significant.
A targeted multivariable binary logistic regression analysis was performed to evaluate whether the association between CAECP and 90-day mortality persisted after adjustment for clinically relevant potential confounders. Given the limited sample size and number of mortality events, the model was deliberately restricted to CAECP status, age, and malignancy. The dependent variable was 90-day mortality. Results were expressed as adjusted odds ratios (aORs) with 95% confidence intervals (CIs) and corresponding P-values.
RESULTS
A total of 286 patient files admitted to the Pulmonology Department with a preliminary diagnosis of pneumonia between April 2023 and March 2025 were retrospectively screened. Two hundred and eighteen patients were excluded for the following reasons: negative culture results (n=132), inability to clearly differentiate malignancy from pneumonia (n=24), non-pneumonia respiratory infections such as bronchiectasis or tracheobronchitis (n=17), and HAP/VAP diagnosis (n=45). The final study cohort comprised 68 hospitalized CAP patients with positive sputum culture results. Subjects were categorized into the CAECP group (n=37) and the Other-CAP group (n=31).
The baseline demographic, clinical, laboratory, and radiological characteristics of the study groups are detailed in Table 1. The median age was 69 (50.7–71) years in the CAECP group (27% females) and 67 (56–70) years in the Other-CAP group (35% females), showing no differences between groups (P=.805 and P=.452, respectively). Although the number of accompanying comorbidities was slightly higher in the CAECP group (100 vs. 90%), the difference was not statistically significant (P=.094). Individual comorbidity rates, including chronic pulmonary disease (P=.841), heart disease (P=.637), kidney disease (P=.525), diabetes mellitus (P=.623), hypertension (P=.761), and malignancies (P=.229), were comparable across both cohorts. On hospital admission, clinical vital signs, including body temperature (P=.970), heart rate (P=.592), systolic (P=.995) and diastolic blood pressures (P=.816), and oxygen saturation (P=.254), were not significantly different between the groups.
Table 1.
Baseline clinical, demographic, laboratory, and radiological characteristics of the study patients.
| Characteristics | CAECP Group (n=37) | Other-CAP Group (n=31) | P value |
|---|---|---|---|
| Demographics | |||
| Age, yearsa | 69 (50.7–71) | 67 (56–70) | .805 |
| Gender, Female/Male (%) | 10 (27) / 27 (73) | 11 (35) / 20 (64) | .452 |
| Presence of comorbidities (%) | 37 (100) | 28 (90) | .094 |
| Specific comorbidities, n (%) | |||
| Chronic pulmonary disease | 17 (46) | 15 (48) | .841 |
| Hypertension | 13 (35) | 12 (39) | .761 |
| Chronic heart disease | 10 (27) | 10 (32) | .637 |
| Extrapulmonary malignancy | 10 (27) | 4 (13) | .229 |
| Diabetes mellitus | 9 (24) | 6 (19) | .623 |
| Chronic kidney disease | 8 (22) | 4 (13) | .525 |
| Chronic neurological disease | 3 (8) | 3 (10) | > .999 |
| Chronic liver disease | 2 (5) | 0 | .496 |
| Lung cancer | 2 (5) | 3 (10) | .653 |
| Other cancers | 6 (16) | 4 (13) | .745 |
| Rheumatological cisease | 1 (3) | 1 (3) | > .999 |
| Clinical characteristics on admission | |||
| Body temperature (°C)a | 36.6 (36.4–36.7) | 36.6 (36.5–36.6) | .970 |
| Heart rate (beats/minute)a | 80 (69–84.2) | 84 (70–85) | .592 |
| Systolic blood pressure (mm Hg)a | 120 (110–128) | 120 (108–131) | .995 |
| Diastolic blood pressure (mm Hg) | 70.8±9.4 | 70.2±11.9 | .816 |
| Oxygen saturation (%) | 93.7±4.1 | 94.71±2.8 | .254 |
| Laboratory parameters on admission | |||
| White Blood Cell count (×109/L)a | 8.9 (5.6–12.3) | 10.5 (8.2–13.8) | .064 |
| Hemoglobin (g/dL) | 10.6±2.4 | 11.2±2.1 | .281 |
| Platelets (×109/L)a | 220 (137–306) | 274 (162–303) | .592 |
| C-reactive protein (mg/L) | 93.4±86.7 | 85.5±99.8 | .731 |
| Procalcitonin (ng/mL)a | 0.35 (0.17–2.79) | 0.54 (0.11–1.84) | .749 |
| Lactate dehydrogenase (U/L)a | 218.5 (200.5–331.2) | 258 (201–447.5) | .751 |
| Urea (mg/dL)a | 26 (16–35) | 21 (14–27.5) | .167 |
| Creatinine (mg/dL)a | 0.99 (0.71–1.62) | 0.92 (0.67–1.28) | .546 |
| Alanine aminotransferase (U/L)a | 15 (9.5–20.5) | 15 (9.7–28.5) | .479 |
| Aspartate aminotransferase (U/L)a | 19.2 (15–32.4) | 22.5 (16–36.7) | .492 |
| Serum albumin (g/L) | 32.8±6.8 | 35.9±6.3 | .063 |
| Radiological features, n (%) | |||
| Multilobar involvement | 30 (81) | 20 (64) | .246 |
| Consolidation | 29 (78) | 22 (71) | .477 |
| Bilateral involvement | 26 (70) | 19 (61) | .465 |
| Ground-glass opacities | 16 (43) | 13 (42) | .923 |
| Pleural Effusion | 14 (38) | 14 (45) | .591 |
| Air bronchogram | 12 (32) | 9 (29) | .938 |
Note: Data presented as n (%) for frequencies and mean±standard deviation (SD) for continuous variables;
denotes median (interquartile range). Significant at P<.05). Abbreviations: CAECP, Community-Acquired Escherichia coli Pneumonia; CAP, Community-Acquired Pneumonia
Regarding laboratory parameters at presentation, the mean serum CRP level was 93.4±86.7 mg/L in the CAECP group and 85.5±99.8 mg/L in the Other-CAP group (P=.731). Mean serum albumin was 32.8±6.8 g/L in the CAECP group and 35.9±6.3 g/L in the Other-CAP group (P=.063). Other laboratory variables, including WBC (P=.064), HGB (P=.281), PLT (P=.594), procalcitonin (P=.749), LDH (P=.751), urea (P=.167), creatinine (P=.546), ALT (P=.479), and AST (P=.492), demonstrated no statistically significant differences between the study groups (Table 1).
Radiological evaluation revealed that multilobar involvement (81% vs. 64%, P=.246) and bilateral pulmonary involvement (70% vs. 61%, P=.465) were more frequent in the CAECP group; however, these differences did not reach statistical significance. Rates of pleural effusion (P=.591), ground-glass opacity (P=.923), air bronchograms (P=.938), and consolidation (P=.477) were likewise comparable between the groups (Table 1).
The initial and maintenance antimicrobial regimens utilized in the study population are presented in Table 2. In the CAECP group, empirical initial antibiotic therapy had to be revised and expanded to a broader-spectrum regimen in 16 patients (43%), whereas treatment expansion was required in only 6 patients (19%) in the Other-CAP group, representing a statistically significant difference (P=.036).
Table 2.
Antimicrobial treatment regimens administered to the study groups.
| Initial Empirical Regimen | Maintenance/Revised regimen | CAECP Group (n=37), n (%) | Other-CAP Group (n=31), n (%) |
|---|---|---|---|
| Ceftriaxone + Macrolide | Ceftriaxone + Macrolide | 1 (3) | 6 (19) |
| Ampicillin-sulbactam + Macrolide | Ampicillin-sulbactam + Macrolide | 1 (3) | 1 (3) |
| Ceftriaxone + Macrolide | Piperacillin-Tazobactam + Macrolide | 5 (14) | 2 (6) |
| Moxifloxacin | Moxifloxacin | 1 (2.7) | 8 (26) |
| Moxifloxacin | Piperacillin-Tazobactam | 2 (5.4) | 0 |
| Ceftriaxone + Macrolide | Meropenem | 3 (8) | 0 |
| Moxifloxacin | Meropenem | 3 (8) | 3 (10) |
| Piperacillin-Tazobactam + Macrolide | Piperacillin-Tazobactam + Macrolide | 4 (11) | 2 (6) |
| Meropenem | Meropenem | 7 (19) | 2 (6) |
| Ceftriaxone + Moxifloxacin | Moxifloxacin | 7 (19) | 4 (13) |
| Piperacillin-Tazobactam + Macrolide | Meropenem | 1 (3) | 1 (3) |
| Ceftriaxone + Macrolide | Trimethoprim-Sulfamethoxazole | 1 (3) | 1 (3) |
| Ceftriaxone + Moxifloxacin | Linezolid | 1 (3) | 1 (3) |
Note: Data presented as n (%). In the CAECP group, treatment was expanded in 16 patients (43%) compared to 6 patients (19%) in the Other-CAP group (P=.036). Abbreviations: CAECP, Community-Acquired Escherichia coli Pneumonia; CAP, Community-Acquired Pneumonia.
Prognostic indicators and clinical outcome parameters are summarized in Table 3. Baseline prognostic scoring systems demonstrated no significant differences between the cohorts: the mean CURB-65 score was 1.73±0.90 in the CAECP group vs. 1.45±0.99 in the Other-CAP group (P=.253), and the mean PSI score was 108.6±40.6 vs. 95.4±27.6, respectively (P=.143). The ICU admission rate was 16% in the CAECP group compared to 10% in the Other-CAP group (P=.494). Despite similar presentation severity scores, the mean length of hospital stay was significantly longer in the CAECP group [15.7±15.5 vs. 9.6±7.0 days, P=.047]. Moreover, in-hospital mortality was modestly higher in the CAECP group, occurring in 5 patients (14), whereas no deaths occurred in the Other-CAP group (P=.058). Overall 90-day mortality was significantly higher in the CAECP group than in the Other-CAP group (49% vs. 16%, P=.005).
Table 3.
Prognostic severity scores and clinical outcomes.
| Prognostic parameter/outcome | CAECP Group (n=37) | Other-CAP Group (n=31) | P value |
|---|---|---|---|
| CURB-65 score | 1.73±0.90 | 1.45±0.99 | .253 |
| PSI score | 108.6±40.6 | 95.4±27.6 | .143 |
| Length of hospital stay, days | 15.7±15.5 | 9.65±7.0 | .047 |
| ICU admission (%) | 6 (16) | 3 (10) | .494 |
| Successfully discharged (%) | 26 (70) | 28 (90) | .069 |
| In-hospital mortality (Exitus) (%) | 5 (14) | 0 | .058 |
| 90-day mortality (%) | 18 (49) | 5 (16) | .005 |
Note: Data presented as mean±SD and n(%); significant at P<.05. Abbreviations: CAECP, Community-Acquired Escherichia coli Pneumonia; CAP, Community-Acquired Pneumonia; CURB-65, Confusion, Urea, Respiratory rate, Blood pressure, Age ≥65; ICU, intensive care unit; PSI, Pneumonia Severity Index.
In the targeted multivariable binary logistic regression analysis, CAECP remained independently associated with 90-day mortality after adjustment for age and malignancy (aOR, 7.413; 95% CI, 1.850–29.712; P=.005). Malignancy was also independently associated with 90-day mortality (aOR, 9.658; 95% CI, 2.151–43.367; P=.003), whereas age was not significantly associated with the outcome (aOR, 1.000; 95% CI, 0.955–1.047; P=.992) (Table 4).
Table 4.
Multivariable logistic regression analysis of factors associated with 90-day mortality in the overall study cohort.
| Variable | β | aOR | 95% CI | P value | |
|---|---|---|---|---|---|
| Lower | Upper | ||||
| Age | .000 | 1.000 | .955 | 1.047 | .992 |
| Malignancy | 2.268 | 9.658 | 2.151 | 43.367 | .003 |
| CAECP | 2.003 | 7.413 | 1.850 | 29.712 | .005 |
| Constant | -.323 | .724 | .842 | ||
Note: Significant at P<.05. β: Regression coefficient, CAECP, Community-Acquired Escherichia coli Pneumonia CI: Confidence Interval, aOR: Adjusted Odds Ratio.
DISCUSSION
In this study, the clinical, demographic, laboratory, and radiological findings, along with baseline prognostic indicators (CURB-65 and PSI scores) and clinical outcomes of patients with CAECP, were compared with those of CAP caused by other pathogens. Our primary finding is that although CAECP mirrors typical CAP in terms of presentation characteristics and initial severity scores, it is associated with a substantially worse prognosis, significantly longer hospitalization, and numerically higher in-hospital and significantly higher 90-day mortality rates.
CAP remains the most common lower respiratory tract infection worldwide and a leading cause of hospitalizations and infection-related deaths. Despite extraordinary advances in healthcare technologies and antimicrobial therapies, mortality rates and the economic burden associated with CAP inpatient care continue to rise. In the majority of clinical cases, identifying the causative pathogen is not possible; consequently, empirical antibiotic therapy is initiated almost universally.13 When selecting empirical agents for CAP, regimens targeting core pathogens such as S. pneumoniae, H. influenzae, M. pneumoniae, S. aureus, C. pneumoniae, Legionella spp., and Moraxella catarrhalis are standardly preferred.14 In patients requiring hospitalization for CAP, treatment failure—indicated by ICU transfer rates and mortality—remains unacceptably high. Although CAP mortality and ICU admission rates vary across studies and geographical regions, they are generally reported between 12%–24% and 1.2%–10%, respectively.15,16
Most previous literature has emphasized E. coli primarily as HAP- or CAP-related infections.17,18 However, updated international consensus guidelines, such as the recent ERS/ESICM/ESCMID/ALAT guidelines on severe CAP, specifically highlight “non-core” pathogens, including Pseudomonas aeruginosa and Enterobacterales (such as E. coli), as critical etiologic agents in severe CAP presentations.5 The limited number of studies and case reports addressing CAECP emphasize that affected patients are generally older (mean age 76 years), male-predominant, and carry a heavier burden of comorbid diseases compared to those with pneumococcal pneumonia.19 In our cohort, although statistical significance was not reached, patients in the CAECP group likewise exhibited higher rates of comorbidities and a male gender predominance compared to the Other-CAP group.
Clinical evidence supports that when E. coli emerges as a CAP pathogen, it leads to increased morbidity and mortality. Marrie et al20 conducted an investigation with a design very similar to ours, comparing CAECP with other forms of CAP. Among 1343 hospitalized CAP patients, they identified E. coli as the etiologic agent in 19 cases. Their CAECP cohort was characterized by older age, female predominance, and a significantly higher incidence of bacteremia. They reported a 90-day mortality rate of 21% in the CAECP group compared to 7.4% in the non-E. coli CAP group; however, likely due to the small number of E. coli cases, this difference did not reach statistical significance. In a more recent and larger retrospective cohort study by John et al,21 among 8680 CAP patients diagnosed via blood or sputum cultures, 1029 (7.7%) were identified as CAECP. The mortality rate in the CAECP group was significantly higher than in the general CAP cohort. The authors attributed this mortality gap to a higher incidence of sepsis, older patient age, greater comorbidity burden, and the potentially enhanced virulence of Gram-negative respiratory pathogens compared to typical CAP organisms.
One of the most notable findings of our study was the higher in-hospital mortality (14% vs. 0%) and significantly higher 90-day mortality (49% vs. 16%) in the CAECP group, which strongly aligns with emerging literature.20,21 We hypothesize that these adverse outcomes stem not only from patient-related factors (such as advanced age, chronic comorbidities, and bacterial virulence) but also from clinical management patterns. Because E. coli is not traditionally considered a primary CAP pathogen, initial empirical antibiotic regimens frequently lack optimal early coverage or are not timely adjusted. Furthermore, there is currently a lack of widespread, standardized clinical guidance specifically addressing the risk stratification and management of CAECP. As noted by John et al,21 even after microbiological confirmation of CAECP, antibiotic regimens were frequently not narrowed or appropriately optimized, reflecting a persistent underappreciation of E. coli as a primary lung pathogen among clinicians.
Importantly, the association between CAECP and 90-day mortality persisted in the targeted multivariable analysis. After adjustment for age and malignancy, CAECP remained independently associated with 90-day mortality (aOR, 7.41; 95% CI, 1.85–29.71; P=.005). Malignancy was also independently associated with 90-day mortality (aOR, 9.66; 95% CI, 2.15–43.37; P=.003), whereas age was not significantly associated with the outcome. These findings suggest that the increased 90-day mortality observed in the CAECP group cannot be explained solely by differences in age or malignancy status. Nevertheless, the relatively small number of outcome events and the wide confidence intervals warrant cautious interpretation and confirmation in larger cohorts.
Our study has several important limitations. Primarily, the single-center, retrospective design and the relatively small sample size limit the statistical power of our subgroup analyses. Due to the retrospective nature of the data collection, comprehensive risk factor stratification and definitive diagnostic framing for CAECP could not be fully established. Moreover, the small sample size may have accounted for the lack of statistical significance in certain variables (such as comorbidity burden and multilobar radiological involvement) where clinical trends were evident.
Detailed information regarding recurrent urinary tract infections, recent urological procedures, structural urinary tract abnormalities, aspiration risk, and specific forms of immunosuppression was not consistently available in the retrospective records; therefore, potential portals of entry and predisposing factors for CAECP could not be systematically analyzed. Although a targeted multivariable analysis was performed, the relatively small sample size and limited number of mortality events restricted the number of covariates that could be included in the model. Therefore, residual confounding by unmeasured or unavailable factors cannot be excluded. Despite these limitations, the present study has several strengths. First, it specifically focused on culture-confirmed community-acquired E. coli pneumonia, a rarely investigated clinical entity, and compared these patients with a culture-positive non-E. coli CAP group. Second, the study evaluated a broad range of clinical, laboratory, radiological, treatment-related, and prognostic variables, including established severity scores and 90-day mortality, providing a comprehensive real-world assessment of CAECP.
CONCLUSION
In conclusion, although it is not a predominant etiologic agent, E. coli must be recognized as a viable pathogen in CAP. As demonstrated in our investigation, CAECP can perfectly mimic typical CAP in its clinical, radiological, and laboratory presentations. Crucially, despite similar baseline CURB-65 and PSI scores, CAECP was associated with significantly higher 90-day mortality. Inhospital mortality was also numerically higher, although this difference did not reach statistical significance. This disparity must be taken into account by pulmonologists, infectious disease specialists, and intensive care physicians. Standardized clinical guidelines are urgently needed to define the specific risk factors, diagnostic approaches, and tailored antimicrobial strategies for CAP caused by E. coli.
SUPPLEMENTS
Supplementary Table 1.
CURB-65 scoring.
| One point is assigned for each of the following criteria: |
|---|
|
Risk categories: 0–1 points, low risk (<3% mortality); 2 points, moderate risk (3%-15% mortality); 3–5 points, high risk (>15% mortality).
Supplementary Table 2.
Pneumonia Severity Index (PSI) scoring elements.
| Metric | Score | Metric | Score |
|---|---|---|---|
| Demographic characteristics | Laboratory findings | ||
| Age, male | Years | BUN ≥10.7 mmol/L | 20 |
| Age, female | Years - 10 | Na <130 mmol/L | 20 |
| Concomitant diseases | Glucose ≥14 mmol/L | 10 | |
| Malignancy | 30 | Hematocrit <30% | 10 |
| Liver disease | 20 | Chest radiograph | |
| Congestive heart failure | 10 | Pleural effusion | 10 |
| Cerebrovascular/cardiovascular disease | 10 | Oxygenation | |
| Kidney disease | 10 | Arterial pH <7.35 | 30 |
| Vital signs | PaO2 <8 kPa | 10 | |
| Confusion | 20 | SaO2 <90% | 10 |
| Respiratory rate ≥30/min | 20 | ||
| Systolic blood pressure <90 mm Hg | 20 | ||
| Temperature <35 degrees C or ≥40°C | 15 | ||
| Heart rate ≥125/min | 10 |
PSI risk classes: Class I, age <50 years and no comorbidities; Class II, <70 points; Class III, 71–90 points; Class IV, 91–130 points; Class V, >130 points. BUN: blood urea nitrogen; Na: sodium; PaO2: arterial oxygen partial pressure; SaO2: oxygen saturation.
Funding Statement
None.
Footnotes
CONFLICT OF INTEREST: None.
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