Risk and prognostic patterns of viral-associated invasive pulmonary aspergillosis: impact of corticosteroid and antibiotic exposure in non-neutropenic hosts

Introduction

Invasive pulmonary aspergillosis (IPA), which is a severe opportunistic infection caused by Aspergillus species, has traditionally been associated to immunocompromised individuals, particularly those with neutropenia or profound immune suppression (1). However, emerging evidence has indicated the rising incidence of IPA among non-neutropenic patients (2). Notably, severe viral pneumonias, including those caused by influenza and coronavirus disease 2019 (COVID-19), have emerged as significant predisposing conditions for viral-associated pulmonary aspergillosis.

Influenza-associated pulmonary aspergillosis (IAPA) was first identified in immunocompetent individuals, but gained clinical prominence following the 2009 novel influenza A (H1N1) pandemic, which established influenza as an independent risk factor for IPA in intensive care unit (ICU) patients, significantly contributing to influenza-related mortality (3). Since the emergence of H1N1, reported IAPA cases have steadily risen, with IPA complicating up to 19.00% of influenza cases. Similarly, COVID-19 pneumonia has been linked to IPA rates, which ranged from 2.80% to 28.50%, particularly in severe cases (4,5). Several regional studies have reported IPA incidences ranging from 19.40% to 33.30% in critically ill COVID-19 patients (6). Viral-associated pulmonary aspergillosis arises from complex interactions among the host, virus, and Aspergillus spp. (7). Host defense begins with the anatomical barriers and mucociliary clearance of inhaled conidia (8). Both influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) compromise this defense by damaging the respiratory epithelium (disrupting cell junctions), impairing mucociliary function, and suppressing antimicrobial responses, such as reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity (9,10). Furthermore, these viruses trigger a cytokine storm, marked by elevated interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF), further weakening epithelial integrity. The resulting barrier disruption facilitates fungal invasion, supported by the histological evidence of Aspergillus colonization near the damaged epithelium in co-infected patients (11).

In critically ill, non-immunosuppressed patients, several factors have been implicated in the development of IPA. Although corticosteroids are occasionally administered in severe influenza, its use may independently increase the risk of IPA (12,13). Similarly, the widespread use of broad-spectrum antibiotics in COVID-19 management may contribute to fungal overgrowth through the disruption of the host microbiota (14,15). Despite these associations, the specific contributions of antibiotic exposure, corticosteroid administration, and cumulative corticosteroid dosage to IPA incidence and clinical outcomes remain incompletely defined. The present retrospective analysis of non-neutropenic patients with H1N1 and COVID-19 examined the impact of antibiotic duration, corticosteroid use, and total corticosteroid dose on the risk and prognosis of IPA, aiming to refine its risk stratification, and elucidate the IPA pathogenesis in this population. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1198/rc).

Methods

Ethics

The present retrospective study was approved by the Ethics Committee of General Hospital of Ningxia Medical University (approval No. KYLL-2025-1354), and conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The requirement for a written informed consent was waived by the Ethics Committee due to the retrospective design of the study and de-identified data.

Subjects

The present retrospective study included only hospitalized adult inpatients with laboratory-confirmed viral infections from the General Hospital of Ningxia Medical University, and excluded outpatient cases. Between December 2019 and December 2024, cases of non-neutropenic viral infections, including influenza and COVID-19, were included. Viral nucleic acid testing was performed for all patients within 72 hours of symptom onset. Influenza diagnosis was based on characteristic influenza-like symptoms and at least one laboratory criterion: (I) detection of viral nucleic acid by molecular methods; (II) antigen detection via immunological assay; (III) viral isolation from clinical specimens; or (IV) a four-fold rise in virus-specific immunoglobulin G (IgG) titers between acute and convalescent sera (16).

COVID-19 was diagnosed through the detection of SARS-CoV-2 ribonucleic acid (RNA) in nasopharyngeal or lower respiratory tract specimens using reverse transcription-polymerase chain reaction (RT-PCR). In addition, co-infection was defined by the concurrent detection of both H1N1 and SARS-CoV-2 nucleic acids within a 7-day interval, accompanied by clinical features consistent with both viral infections. Since December 2019, the General Hospital of Ningxia Medical University has been implementing mandatory combined RT-PCR screening for influenza and SARS-CoV-2 for all inpatients. Consequently, the co-infection detection rate observed in the present hospitalized cohort (27.40%) exceeded the community-level prevalence. All diagnostic tests were RT-PCR-based, and antigen detection assay was not used to prevent potential cross-reactivity.

IPA diagnostic criteria: participants were eligible for inclusion when they were ≥18 years old, and met the diagnostic criteria for IPA, as defined by established guidelines (17). The diagnosis of confirmed IPA required at least one of the following: (I) histopathological or cytopathological evidence of hyphal invasion consistent with Aspergillus spp. in specimens obtained from sterile sites, such as lung tissue acquired via biopsy or needle aspiration; or (II) a positive culture for Aspergillus spp. from sterile-site specimens linked to the infection. A diagnosis of possible or suspected IPA necessitated the simultaneous presence of both: (I) clinical features, including persistent fever unresponsive to broad-spectrum antibiotics for >3 days, recurrent intermittent fever, pleuritic chest pain, dyspnea, hemoptysis, or progressive respiratory deterioration; and (II) evidence of host risk factors, such as influenza or COVID-19 infection, moderate-to-severe chronic obstructive pulmonary disease (COPD), decompensated liver cirrhosis, or uncontrolled human immunodeficiency virus (HIV) infection (CD4⁺ <0.5×10⁹/L), or a galactomannan optical density index (ODI) of ≥1.0 in bronchoalveolar lavage fluid (BALF).

Patients were excluded when essential clinical data was incomplete, including corticosteroid dosage (Table S1 for conversion), treatment duration, or antibiotic use. Additional exclusion criteria included hospital stay of <24 hours, neutropenia (absolute neutrophil count <0.50×10⁹/L), and profound immunosuppression, such as advanced HIV infection, recipients of hematopoietic stem cell or solid organ transplants, or patients receiving intensive immunosuppressive therapy.

Data collection

The clinicopathological characteristics were systematically collected across six domains: demographic data (age and gender), comorbidities (including diabetes mellitus and chronic respiratory diseases), laboratory parameters (such as complete blood count, C-reactive protein, and procalcitonin levels), and arterial blood gas measurements. The therapeutic data comprised of the duration of antibiotic exposure, corticosteroid dosage, and length of corticosteroid therapy, which was defined as a cumulative exposure of up to 24 hours prior to the diagnosis of IPA. A subgroup analysis was conducted based on the presence of mild immunosuppression, which was defined as uncontrolled diabetes [hemoglobin A1c (HbA1c) >9%] or low-dose immunosuppressive therapy (prednisone <10 mg/day or equivalent).

Statistical analysis

Statistical analysis was performed using the R software (version 4.3.2). Descriptive statistics were reported in count and percentage for categorical variables, mean with standard deviation for normally distributed continuous variables, and median with interquartile range (IQR) for non-normally distributed data. Continuous variables were compared using one-way analysis of variance (ANOVA) or Kruskal-Wallis test, as appropriate, while categorical variables were compared using Chi-squared test. Nonlinear associations were assessed using restricted cubic spline modeling. A P value of <0.05 was considered indicative of statistical significance.

Results

Baseline characteristics

A total of 234 non-neutropenic patients with confirmed viral infections were included in the present study. The flow chart is as follows (Figure 1). These patients were stratified into three groups: co-infection group (n=64), COVID-19 group (n=74), and H1N1 group (n=96).

Figure 1 Study cohort and design overview. The flowchart illustrates the patient selection, inclusion/exclusion criteria, stratification by infection type, and final cohort composition. COVID-19, coronavirus disease 2019; H1N1, novel influenza A; IPA, invasive pulmonary aspergillosis; RCS, restricted cubic spline.

Comparison between IPA and non-IPA patients

After comparing patients with IPA (n=152) to patients without IPA (n=82), several significant differences emerged (Table 1). Corticosteroid exposure was markedly more prevalent in the IPA group (72.00% vs. 45.00%, P<0.001), as well as antibiotic usage (55.00% vs. 3.70%, P<0.001). Furthermore, comorbid conditions were more frequent in patients with IPA, with higher rates of diabetes mellitus (70.00% vs. 27.00%, P<0.001) and underlying respiratory disease (61.00% vs. 32.00%, P<0.001). Moreover, ICU admission was substantially more common in the IPA group (64.00% vs. 26.00%, P<0.001).

Comparison of the co-infection, COVID-19 and H1N1 groups

IPA developed in 57 (89.00%) patients in the co-infection group, 31 (42.00%) patients in the COVID-19 group, and 64 (67.00%) patients in the H1N1 group (Table 2), yielding an overall IPA incidence of 152 cases.

Significant differences in baseline characteristics emerged across the three groups (Table 2). The co-infection group had the highest rates of corticosteroid use (75.0%) and antibiotic administration (48.0%), when compared to the H1N1 (61.0% and 36.0%) and COVID-19 (54.0% and 27.0%) groups (P=0.04 and P=0.03, respectively). Pre-existing respiratory diseases were most prevalent in the co-infection group (63.0%), exceeding those in the COVID-19 (32.0%) and H1N1 (57.0%) groups (P<0.001). Hypoproteinemia was frequent in the H1N1 (63.0%) and co-infection (56.0%) groups, surpassing that in the COVID-19 group (36.0%) (P=0.003).

Furthermore, the cumulative corticosteroid dose was significantly higher in the co-infection group (P<0.001). Mortality was markedly elevated in the co-infection group (36.0%), when compared to the COVID-19 (12.0%) and H1N1 (8.3%) groups (P<0.001). The laboratory data revealed a significantly lower white blood cell (WBC) count (P=0.02), alongside the higher disease severity reflected by the Sequential Organ Failure Assessment (SOFA, P<0.001) and Acute Physiology and Chronic Health Evaluation II (APACHE II, P=0.002) scores. The ICU admission rates were highest in the co-infection group (73.0%, P<0.001).

Prognosis of patients with IPA secondary to viral pneumonia

For patients with viral-associated IPA, the prevalence of underlying respiratory disease was highest in the H1N1 group (69.00%), followed by the co-infection group (67.00%) and COVID-19 group (35.00%) (P=0.004). Hypoalbuminemia was the most common in the H1N1 group (73.00%), when compared to the co-infection group (54.00%) and COVID-19 group (52.00%) (P=0.04). Mortality was significantly higher in the co-infection group (37.00%), when compared to the COVID-19 group (9.70%) and H1N1 group (9.40%) (P<0.001, Table 3). The co-infection group had prolonged corticosteroid exposure (P=0.008), extended antibiotic treatment (P=0.01), and higher cumulative corticosteroid doses (P=0.002). Furthermore, the co-infection group had significantly elevated SOFA (P=0.001) and APACHE II (P=0.004) scores, indicating greater clinical severity. The Kaplan-Meier (KM) analysis revealed a significantly reduced median survival in the co-infection group, when compared to the COVID-19 and H1N1 groups (log-rank P<0.001). Patients with IPA due to COVID-19 or H1N1 alone had a substantially lower mortality risk, when compared to patients with combined infections (Figure 2, Table 4).

Figure 2 Survival analysis and treatment exposure comparisons in invasive pulmonary aspergillosis. (A) Kaplan-Meier survival curves stratified by infection type; (B) box plots for corticosteroid exposure duration, cumulative dosage, and antibiotic duration by group. COVID, coronavirus disease; H1N1, novel influenza A; IPA, invasive pulmonary aspergillosis.

Diagnostic staging, pathogen distribution, and antifungal therapy by viral infection type

A total of 152 patients with IPA were included for the present study. The diagnostic staging, pathogen profiles, and antifungal regimens are summarized in Table 3.

Diagnostic staging

Overall, 6 patients (3.90%) were classified as proven IPA, 89 patients (58.60%) were classified as probable IPA, and 57 patients (37.50%) were classified as possible IPA. The proportion of proven IPA was highest in the co-infection group (5.30%), followed by the COVID-19 (3.20%) and H1N1 (3.10%) groups. For patients with probable and possible IPA:

• Co-infection group: 57.90% (33/57) had probable IPA, and 36.80% (21/57) had possible IPA;
• COVID-19 group: 58.10% (18/31) had probable IPA, and 38.70% (12/31) had possible IPA;
• H1N1 group: 59.40% (38/64) had probable IPA, and 37.50% (24/64) had possible IPA.

Pathogen distribution

Among the 95 cases (proven + probable) with culture or polymerase chain reaction (PCR)-confirmed Aspergillus species, Aspergillus fumigatus (A. fumigatus) was the predominant (81/95, 85.30%), followed by Aspergillus flavus (7/95, 7.40%), Aspergillus niger (4/95, 4.20%), and the Aspergillus terreus complex (3/95, 3.10%). The distribution of Aspergillus species significantly varied among the groups (P<0.05), with A. fumigatus as the most prevalent in the H1N1 group (57.80%), followed by the COVID-19 (51.60%) and co-infection (49.10%) groups.

Antifungal therapy

Voriconazole was the most commonly used first-line antifungal (108/152, 71.10%), followed by isavuconazole (22/152, 14.50%) and liposomal amphotericin B (15/152, 9.90%). Other regimens (including caspofungin, micafungin, and combination therapies) were used in 4.60% (7/152) of patients.

Association of corticosteroid/antibiotic exposure with IPA risk and mortality across viral infections

IPA occurrence

In the co-infection group, corticosteroid duration clustered at 8–10 days, with a significant non-linear, but non-significant, overall association (P_non-linear =0.02, P_overall =0.07; Figure 3A). IPA risk followed a U-shaped curve with minimum risk (approximately 0.25) at 338.30 mg [95% confidence interval (CI): 262.60–574.80, Figure 3B]. The inverted U-shaped association between antibiotic exposure and IPA risk in the co-infection group is depicted in Figure 3C; however, this relationship did not reach statistical significance (P_non-linear >0.99, P_overall >0.99).

Figure 3 Corticosteroid and antibiotic exposure in co-infected patients: associations with IPA risk. (A) Non-linear association between corticosteroid exposure duration and IPA occurrence; (B) U-shaped relationship between cumulative corticosteroid dose and IPA risk; (C) inverted U-shaped association between antibiotic exposure duration and IPA incidence. CI, confidence interval; IPA, invasive pulmonary aspergillosis; RCS, restricted cubic spline.

In the H1N1 group, corticosteroid duration and antibiotic exposure presented with inverted U-shaped associations, with a peak IPA probability (approaching to 1.00) at 5–15 and 5–10 days, respectively (P_non-linear <0.001, P_non-linear =0.003 Figure 4A,4B). The cumulative corticosteroid dose again demonstrated a U-shaped trend, with the lowest risk (approximately 0.25) at 265.40 mg (95% CI: 239.60–532.10, Figure 4C).

Figure 4 Exposure-response trends in 2009 novel influenza A-associated IPA. (A) Inverted U-shaped association between corticosteroid exposure duration and IPA risk; (B) non-linear relationship between antibiotic exposure duration and IPA occurrence; (C) U-shaped curve showing IPA risk by cumulative corticosteroid dose. IPA, invasive pulmonary aspergillosis; RCS, restricted cubic spline.

In the COVID-19 group, the corticosteroid duration peaked in IPA risk (approaching to 1.00) at approximately 10 days, decreasing at shorter/longer exposures (P-non-linear<0.001, Figure 5A). The cumulative dose exhibited a U-shape, with minimum risk at ~273.50 mg (95% CI: 262.60–574.80, Figure 5B). As shown in Figure 5C, a similar non-significant trend was observed for antibiotic duration in the COVID-19 group (P_non-linear =0.98, P_overall >0.99).

Figure 5 Therapeutic exposure and IPA risk in coronavirus disease 2019 patients. (A) Corticosteroid duration and its peak association with IPA incidence; (B) U-shaped relationship between corticosteroid dose and IPA risk; (C) association between antibiotic duration and IPA risk. CI, confidence interval; IPA, invasive pulmonary aspergillosis; RCS, restricted cubic spline.

The contour plots highlighted the differential risk zones. In the H1N1 group, IPA incidence was linked to shorter antibiotic and moderate corticosteroid exposure, while in the COVID-19 group, prolonged exposure to both agents correlated to higher risk (Figure 6A). Furthermore, in the H1N1 group, dense red contours at 5–15 days for both exposures suggested an elevated IPA risk or data clustering (Figure 6B). In the COVID-19 group, a similar clustering appeared at 10–20 days (corticosteroids) and 5–15 days (antibiotics), indicating a distinct exposure-risk pattern (Figure 6C). Additionally, comparisons of corticosteroid exposure time, dosage, and antibiotic exposure time across the different infection groups (Figure 6D).

Figure 6 Interaction patterns of corticosteroid and antibiotic exposure in IPA development. (A) Interaction trends of corticosteroid and antibiotic exposure durations; (B) contour plot showing the IPA risk zones for 2009 novel influenza A; (C) contour plot showing the IPA risk zones for coronavirus disease 2019; (D) the box plots compare the corticosteroid exposure time, dosage, and antibiotic duration across groups. COVID, coronavirus disease; H1N1, novel influenza A; IPA, invasive pulmonary aspergillosis.

IPA mortality

In the co-infection group, mortality followed an inverted U-shape by corticosteroid duration, peaking (approximately 0.75) at 8.40 days (95% CI: 7.20–9.80, Figure 7A). Furthermore, the dose-dependent mortality declined to below 400 mg, and subsequently rose sharply beyond 600 mg (95% CI: 642.80–681.80, Figure 7B). Moreover, antibiotic-related mortality peaked (approximately 0.65) at 5.60 days (95% CI: 4.10–8.30, Figure 7C).

Figure 7 Prognostic impact of therapeutic exposure in co-infected invasive pulmonary aspergillosis patients. (A) Corticosteroid duration and mortality risk; (B) mortality by cumulative corticosteroid dose; (C) antibiotic exposure duration and associated mortality risk. CI, confidence interval; RCS, restricted cubic spline.

Similar trends were observed in the H1N1 group. Corticosteroid duration and dose followed inverted U and U-shaped curves, with a peak mortality (approximately 0.50) at 8.70 days and inflection beyond 600 mg (95% CI: 653.50–681.00, Figure 8A,8B). Antibiotic exposure had a peak (approximately 0.45) at 5.30 days (P_non-linear =0.003, P_overall =0.05; Figure 8C).

Figure 8 The 2009 novel influenza A-associated invasive pulmonary aspergillosis: therapeutic exposure and survival outcomes. (A) Corticosteroid exposure duration and mortality; (B) mortality trends by corticosteroid dosage; (C) non-linear relationship between antibiotic duration and mortality. CI, confidence interval; RCS, restricted cubic spline.

In the COVID-19 group, peak mortality (approximately 0.50) occurred at 8.40 days (95% CI: 7.00–10.00, Figure 9A). Furthermore, mortality declined to below ~400 mg of corticosteroid, and subsequently rose steeply beyond ~600 mg (95% CI: 646.30–677.20, Figure 9B). Antibiotic exposure had a non-significant peak (approximately 0.40) at 7.20 days (P_non-linear =0.003, P_overall =0.08; Figure 9C).

Figure 9 Coronavirus disease 2019-associated invasive pulmonary aspergillosis: therapeutic exposures and mortality patterns. (A) Corticosteroid duration and risk of death; (B) dose-dependent mortality curve for corticosteroids; (C) mortality pattern with antibiotic exposure duration. CI, confidence interval; RCS, restricted cubic spline.

Subgroup analysis of mild immunosuppression

A subgroup analysis was conducted for patients with mild immunosuppression (Table 5). No significant differences in IPA-related mortality were observed between the mildly immunosuppressed group and non-immunosuppressed group (24.10% vs. 17.30%, P=0.43). Similarly, the KM analysis results revealed no differences in survival curves (log-rank P=0.80, Figure 10).

Figure 10 Kaplan-Meier survival analysis for patients with mild immunosuppression.

Subgroup analysis of chronic respiratory diseases

Among the 234 included patients, 119 patients (50.9%) had underlying chronic respiratory diseases, primarily COPD, asthma, and bronchiectasis. Compared to patients without chronic respiratory disease, patients with such comorbidities had significantly higher ICU admission rates (61% vs. 40%, P=0.002) and greater incidences of IPA (78% vs. 51%, P<0.001) (Table 6).

In order to assess the individual contributions of risk factors under differing pulmonary baselines, the interaction effects of comorbidities in patients with and without chronic respiratory diseases (Figure 11A). For patients without chronic respiratory disease, diabetes was significantly associated to increased risk of IPA [hazard ratio (HR): 2.77, 95% CI: 1.39–5.53]. In contrast, no additional risk factors reached significance in patients with chronic respiratory disease, suggesting that chronic lung pathology may act as a dominant driver of IPA risk, potentially masking the effects of other comorbidities.

Figure 11 Risk analysis and IPA onset in patients with chronic lung disease. (A) The interaction effects of comorbidities in patients with and without chronic respiratory diseases; (B) the Kaplan-Meier curves show the earlier IPA onset and higher 28-day cumulative incidence in patients with chronic respiratory conditions. CI, confidence interval; IPA, invasive pulmonary aspergillosis.

The KM analysis results further indicated that patients with chronic respiratory disease developed IPA earlier, and had a significantly higher 28-day cumulative incidence, when compared to patients without underlying lung conditions (log-rank P=0.001, Figure 11B).

Discussion

In recent years, beyond traditional risk factors, emerging contributors to IPA have been recognized. Chief among these is the widespread use of biologics and viral co-infections, particularly with influenza and SARS-CoV-2, even in the absence of clearly defined immunosuppression (12,18-20). Influenza, especially H1N1, markedly increases IPA risk, with incidence rising from 5.00% to 14.00%, when compared to immunocompetent individuals with community-acquired pneumonia (21,22). IPA in this context is associated to high mortality, reaching 50–60% (23). H1N1 induces more severe epithelial damage than seasonal strains, enabling the rapid bronchial-to-parenchymal spread of Aspergillus, culminating in extensive pulmonary injury (24,25). Similarly, in severe COVID-19, the viral disruption of epithelial and alveolar structures facilitate fungal invasion (26).

Several important findings were identified in the present comprehensive analysis: (I) patients with H1N1/COVID-19 co-infection had significantly higher disease severity and mortality, with elevated SOFA and APACHE II scores, and a 37.00% mortality rate, substantially exceeding that of H1N1 or COVID-19 alone; (II) corticosteroid and antibiotic exposures had nonlinear relationships with IPA risk and mortality, with moderate durations and cumulative doses correlating to peak risk; (III) underlying conditions, such as COPD and hypoalbuminemia, were prevalent in IPA cases, and contributed to host vulnerability. These findings underscore the complex interplay among viral infection, therapeutic interventions, and host susceptibility in the development of IPA.

COPD, hypoalbuminemia, and viral co-infection emerged as prominent predisposing factors for IPA in non-neutropenic patients. In the present cohort, COPD was the most prevalent underlying respiratory condition. Given the chronic inflammation and impaired mucociliary clearance characteristic of COPD, the pulmonary defense against fungal spores is markedly compromised, thereby facilitating Aspergillus colonization, and subsequent biofilm formation (27). The subgroup analysis revealed the significantly elevated risk of IPA in patients with chronic lung disease, highlighting structural airway damage and impaired clearance mechanisms as key susceptibility factors, independent of immunosuppressive status. Notably, hypoalbuminemia was observed in 63.00% of patients in the H1N1 group, exceeding the 56.00% prevalence in the co-infection group. However, the latter group had a markedly higher mortality rate, suggesting that hypoalbuminemia alone does not account for the observed outcomes. Previous evidence has associated hypoalbuminemia with an increased risk of invasive fungal infections (28). The present findings revealed that the clinical severity in co-infected patients substantially exceeded that of single-pathogen infections. The co-infection group had higher rates of underlying respiratory disease, and more frequent use of corticosteroids and antibiotics, when compared to the H1N1 and COVID-19 groups. Correspondingly, both the SOFA and APACHE II scores were significantly elevated in this cohort. Prognostically, the mortality rate of co-infected patients reached 37.00%, considerably surpassing that of patients with H1N1 (9.40%) and COVID-19 (9.70%), and underscoring the deleterious impact of viral-fungal co-infections on patient outcomes.

The present study further identified a U-shaped association between cumulative corticosteroid dosage and risk of IPA, as demonstrated by the restricted cubic spline analysis. Specifically, IPA risk declined at lower corticosteroid doses, but sharply increased at higher levels, lending support to the hypothesis proposed by Peghin et al. (29), in which elevated corticosteroid exposure may facilitate Aspergillus invasion. These findings underscore the dual-edged nature of corticosteroids: although short-term, low-dose administration may help suppress cytokine storms, while prolonged or high-dose usage would substantially impair host immune defenses, predisposing patients to opportunistic infections, such as IPA. Notably, the temporal dynamics of corticosteroid exposure further influenced IPA risk. In patients with H1N1 infection, the highest risk was observed when corticosteroid treatment lasted for 5–15 days. In contrast, COVID-19 patients presented with a peak in IPA risk at approximately 10 days of exposure. This divergence likely reflects the virus-specific immune modulation, with influenza inducing acute immunosuppression, and SARS-CoV-2 promoting prolonged immune exhaustion through sustained inflammatory responses. The inappropriate use of corticosteroids in clinical practice, such as excessive dosing or unwarranted treatment durations, contributes to the increased incidence of IPA, and worsens patient outcomes. Although corticosteroids are indispensable in modulating immune responses and mitigating inflammatory injury, its potential to compromise antifungal immunity highlights a critical therapeutic paradox in the pathogenesis of IPA. Both the duration and cumulative dose of corticosteroid exposure are pivotal determinants of IPA occurrence and prognosis. Therefore, corticosteroid therapy should be judiciously tailored to the nature of the underlying infection and individual patient profiles. In H1N1-infected patients, careful evaluation of the risk-benefit ratio is imperative. When corticosteroid use is clinically unavoidable, repeated screening for IPA may be warranted (30). In the context of COVID-19, gradual tapering or discontinuation of corticosteroids might be considered in patients with host risk factors for IPA, although present evidence remains insufficient to definitively guide this approach (31).

Similarly, antibiotic exposure had a nonlinear relationship with IPA risk and prognosis. In the H1N1 group, the incidence of IPA peaked when antibiotic use lasted for 5–10 days. This finding suggests that short-term antibacterial therapy may predispose patients to fungal colonization. Prolonged or repeated use of broad-spectrum antibiotics can impair intestinal colonization resistance, leading to fungal overgrowth (including Aspergillus spp.) and translocation, thereby facilitating invasive fungal infections, such as IPA (32). These observations underscore the necessity of stringent antibiotic stewardship throughout the course of treatment. Upon confirmation of the viral etiology, prompt de-escalation or discontinuation of empirical antibiotic therapy should be undertaken to minimize dysbiosis, and reduce the risk of secondary fungal infections. Furthermore, in patients with viral-bacterial co-infections, the association between antibiotic duration and mortality appeared more complex, with the highest risk observed at approximately 5.60 days. This pattern suggests that viral co-infections may exert synergistic immunosuppressive effects, impairing host defense mechanisms, and diminishing resistance to fungal pathogens, thereby adversely affecting clinical outcomes. For this high-risk population, early screening for IPA is warranted, along with intensified supportive care measures, including nutritional optimization and organ function preservation.

The present study had several limitations. First, the retrospective, single-center design of the study may have introduced selection bias, thereby limiting the generalizability of the findings. Second, diagnostic uncertainty remains, since some cases were classified as possible IPA, rather than proven IPA, increasing the risk of misclassification. Third, the analysis was limited to H1N1 and SARS-CoV-2 infections, and excluded other respiratory viruses that may also predispose to IPA. Consequently, prospective studies that encompass a broader viral spectrum are needed to validate these findings, and further elucidate the pathogenesis and progression of viral-associated IPA.

Conclusions

The present study underscores the interplay between viral pneumonia, host factors, and therapeutic exposures in the development of IPA in non-neutropenic patients. Corticosteroid and antibiotic use had non-linear associations with IPA risk and mortality, with moderate exposures posing the highest risk. Co-infection with H1N1 and SARS-CoV-2 was linked to greater disease severity and mortality, particularly in patients with COPD or hypoalbuminemia. These findings highlight the importance of cautious corticosteroid and antibiotic use, and the need for early identification of high-risk individuals. Prospective multi-center studies are needed to validate these results, and guide the optimal management of viral-associated IPA.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1198/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1198/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1198/prf

Funding: This work was supported by the National Natural Science Foundation of China (No. 82360022, to J.Z.), and the Ningxia Key Research and Development Project (Nos. 2022BEG03102 and 2024BEH04027, to J.Z.).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-1198/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of the General Hospital of Ningxia Medical University (approval No. KYLL-2025-1354). Given its retrospective nature and the absence of access to identifiable personal information, the Ethics Committee waived the requirement for a written informed consent.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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