Invasive pulmonary aspergillosis in the intensive care unit: current challenges and best practices

The prevalence of invasive pulmonary aspergillosis (IPA) is growing in critically ill patients in the intensive care unit (ICU). It is increasingly recognized in immunocompetent hosts and immunocompromised ones. IPA frequently complicates both severe influenza and severe coronavirus disease 2019 (COVID‐19) infection. It continues to represent both a diagnostic and therapeutic challenge and can be associated with significant morbidity and mortality. In this narrative review, we describe the epidemiology, risk factors and disease manifestations of IPA. We discuss the latest evidence and current published guidelines for the diagnosis and management of IPA in the context of the critically ill within the ICU. Finally, we review influenza‐associated pulmonary aspergillosis (IAPA), COVID‐19‐associated pulmonary aspergillosis (CAPA) as well as ongoing and future areas of research.


INTRODUCTION
Invasive pulmonary aspergillosis (IPA) is an opportunistic infection caused by a saprophytic airborne filamentous fungus of the Aspergillus species (1,2).Although it usually affects severely immunocompromised patients, it is now increasingly recognized in critically ill patients without the classical host factors that predispose them to invasive fungal diseases such as neutropenia, acquired immunodeficiency syndrome (AIDS)/human immunodeficiency virus (HIV), haematological malignancies, haematopoietic stem cell transplant (HSCT) or solid organ transplantation recipients (3,4).There is a rising incidence of IPA co-infection in patients with influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) (5,6).Globally, over 30 million people are at risk of IPA each year as a result of corticosteroid use or other immunosuppressive therapies.It is estimated that more than 300,000 patients develop IPA per year with at least 125,000 of these cases occurring in patients with chronic obstructive pulmonary disease (COPD).Mortality rates have been reported to exceed 90% of cases (7).In this review, we discuss current evidence and guidelines on IPA in the context of critically ill patients within the ICU.Furthermore, we discuss influenza-associated pulmonary aspergillosis (IAPA), COVID-19-associated pulmonary aspergillosis (CAPA) and delve into potential future research directions.

EPIDEMIOLOGY
The epidemiology of IPA has shifted over the last 20 years due to the increasing number of solid organ transplants, stem cell transplantation recipients and newer immunosuppressive agents (3,8).Aspergillus fumigatus is the most common species implicated in invasive aspergillosis, alongside other notable non-fumigatus species such Aspergillus flavus, Aspergillus terreus, Aspergillus Niger and Aspergillus versicolor (8).In several studies, Aspergillus spp.has been isolated in up to 7% of critically ill, mechanically ventilated patients within ICU and only half of these patients demonstrate findings consistent with invasive aspergillosis as defined by autopsy studies or the EORTC/MSG criteria (2019) (9)(10)(11)(12).
Very few studies describe the epidemiology of invasive aspergillosis within mechanically ventilated patients in ICU.A retrospective cohort study from the United States found risk factors for the development of IPA included corticosteroid use and either respiratory or kidney failure (3).Mortality rates were reported to be as high as 46% and associated with a 3.5% increase in costs with a longer length of stay (LOS).In a different multicentre study based in Italy, major factors predisposing patients to invasive aspergillosis included previous corticosteroid use on a background of autoimmune disease or COPD (13).Other multi-centre, observational studies noted that immunosuppression, sepsis and/or acute respiratory distress syndrome (ARDS) were common factors in patients with proven invasive aspergillosis (14).
Faced with diagnostic challenges, autopsy studies help to fully delineate the scope and susceptibility factors of IPA in the ICU.In one such study that spanned 25 years, 25 patients (2.8%) were diagnosed with IPA at autopsy of which only 10 (40%) had been classified as IPA ante-mortem, based on the initiation of antifungal treatment (15).The most common comorbid conditions associated with this postmortem diagnosis were again corticosteroid treatment (56%), COPD (44%), immunosuppression (24%) and haematological malignancy (20%).

RISK FACTORS
Table 1 summarizes known risk factors for IPA.The immune status of the affected host plays a central role in the pathogenesis of invasive aspergillosis.In patients with profound or prolonged neutropenia post-chemotherapy or as result of allogeneic HSCT, Aspergillus growth in the lung leads to colonization of the upper respiratory tract.This in turn leads to tissue destruction, angioinvasion, a septic state in its final phase, circulating galactomannan and sometimes haemoptysis (Fig. 1).The clinical presentation is relatively rapid, ranging from days to weeks (16).In the nonneutropenic host, invasive aspergillosis is most likely to develop following prolonged use of corticosteroids, commonly observed in critically ill patients in ICU, solid organ transplant recipients, patients with comorbidities such as AIDS/HIV, renal failure, COPD, diabetes and malnutrition (4,17,18).Angioinvasion is not a common feature; instead, pyogranulomatous inflammation and inflammatory necrosis occur.As the condition progresses over weeks to months, based on the degree of patient immunosuppression, many cases of invasive aspergillosis are overlooked and most often diagnosed postmortem (18,19).

DISEASE CLASSIFICATION
Pulmonary aspergillosis can be subdivided into three broad categories: allergic bronchopulmonary aspergillosis (ABPA), chronic pulmonary aspergillosis (CPA) and invasive pulmonary aspergillosis (IPA) (19).For this review, ABPA and CPA will be discussed in brief.ABPA is mostly observed in patients with a history of asthma, cystic fibrosis, COPD and lung transplantation.Hypersensitivity toward Aspergillus fumigatus occurs through TH2 CD4 T-cell response, which in turn activates a cascade of inflammatory cytokines and cells.Patients present with a chronic productive cough or wheeze and have radiological findings significant for recurrent pulmonary infiltration or bronchiectasis.CPA also presents similarly to ABPA, generally affecting patients with immunocompromised status and a pre-existing lung condition.Diagnosis is based on both clinical and radiological findings which need to be present for a minimum of 3 months.CPA exists in many forms including simple aspergilloma, aspergillus nodules, chronic cavitary pulmonary aspergillosis, chronic fibrosing pulmonary aspergillosis and subacute invasive aspergillosis.Lastly, IPA occurs in severely immunocompromised hosts, with Aspergillus fumigatus accounting for the vast majority of observed cases with an estimated mortality rate >50%.Patients under mechanical ventilation are easily susceptible to aspergillus due to structural changes to their bronchial wall and impairment of their usual mucociliary clearance (20).
The most common initial clinical manifestation of invasive aspergillosis is the 'halo sign' represented by solid micro nodules surrounded by area of haemorrhage.Presence of the 'halo sign' confers greater survival rate as patients respond readily to therapy (21).

DISEASE MANIFESTATIONS
Disease manifestations of invasive aspergillosis are often nonspecific, varying greatly from one patient to another (22).Characteristically, invasive aspergillosis begins in the lungs before travelling through the bloodstream to potentially affect other organs such as the brain, kidneys, heart and skin.Affected patients can develop symptoms such as fever, chills, wheezing, cough and shortness of breath (23).Pleuritic chest pain or haemoptysis can allude to the invasion of the pulmonary vasculature leading to thrombosis and haemorrhagic infarction.Severe life-threatening complications such as pulmonary infiltrates, ARDS, shock, organ failure and tracheobronchitis leading to airway obstruction occur frequently in ICU patients (24).Where early diagnosis is critical and challenging in mechanically ventilated patients, algorithms such as the AspICU algorithm allow for more ease in the discrimination of Aspergillus colonized patients from patients with probable invasive pulmonary aspergillosis (25).

CO-INFECTION WITH ASPERGILLOSIS
Using metagenomic next-generation sequencing along with traditional pathogen detection, it has been shown in one study that as many as 40.3% of patients may have pulmonary fungal and bacterial co-infection (26).A clue to co-infection is that the proportion of pulmonary cavitation may be significantly higher in the co-infection than in the fungal infection group.Lymphopenia could be an indicator for co-infection in the elderly patients with IPA (27).Compared with a single pathogen infection, a differential immune response is mounted when patients are infected with multiple pathogens, and this may lead to different clinical outcomes.A retrospective cohort study showed that compared with P. aeruginosa infection alone, A. fumigatus and P. aeruginosa co-infection caused more rapid decline in patients with lung function and worsened clinical outcomes (28).Co-infection is closely associated with mortality (27).
Three cohort studies performed in Belgium and the Netherlands showed that influenza-associated aspergillosis (IAA) had occurred in 16%-23% of influenza patients in the intensive care unit (ICU) (24,29,30).IAA has been diagnosed in those with both with influenza A and influenza B pneumonia, and the use of corticosteroids before ICU admission appears to be an independent risk factor (24).Although the incidence is higher in those who are immunocompromised, in up to 30% of cases, there may be no underlying condition present (30).It has been associated with 4 times greater risk of ICU mortality even when corrected for APACHE II score (5).Invasive tracheobronchial aspergillosis (ITBA) is a rare but severe form of invasive pulmonary aspergillosis that can complicate influenza infection (31).In ITBA, the fungal infection is entirely or predominantly confined to the tracheobronchial tree.It is associated with greater severity, mortality, and serum and BAL fluid galactomannan and 1,3-b-d-glucan concentrations compared to invasive pulmonary aspergillosis without tracheobronchial lesions.It remains unclear whether antifungal prophylaxis reduces the incidence of IAPA (32).
It is more challenging to ascertain the true epidemiology of Coronavirus disease 2019 (COVID-19)associated pulmonary aspergillosis (CAPA) as various definitions were used in studies (including EORTC/MSGERC, AspICU, ECMM/ISHAM) and during the 'first wave' in early 2020, bronchoscopy was considered contraindicated in many centres which probably led to under-reporting.On the contrary, the criteria for defining CAPA relies on mycology which may in turn may result in over-reporting.Treatment modalities have also evolved rapidly over time which may impact on risk and incidence.In a multinational study of 592 critically ill COVID-19 patients, the median prevalence of CAPA per centre was 10.7% (33).The prevalence of CAPA was greater among older patients, mechanically ventilated patients and patients receiving tocilizumab.It was again an independent strong predictor of ICU mortality.
The multicentre MYCOVID study focused entirely on mechanically ventilated patients and found the prevalence of CAPA to be higher at 15% with a very high mortality of 45Á8% observed (15).The combination of dexamethasone and antiinterleukin-6 therapy was associated with a nearly threefold increased risk of CAPA.
Antifungal therapy is recommended in CAPA, while discontinuing or tapering of concomitant corticosteroids therapy could be considered in patients who do not respond (34).The prevalence of pulmonary aspergillosis in COVID-19 patients appears to be comparable to that of pneumococcal pneumonia but substantially lower than the level of coinfection that has been observed in influenza (35).There are some key differences between IAPA and CAPA as summarized in Table 2 (36).

DIAGNOSIS Definitions for diagnosis
The European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) first defined the criteria for probable invasive fungal disease in 2008 (37).Overtime, with recent advances in the diagnosis and management of IPA this led to the publication of revised definitions in 2020 (38).The revised definition has limited applicability in the ICU setting as it primarily focuses on the neutropenic patient with underlying haematological malignancies, solid organ transplant recipients and severely immunosuppressed.These diagnostic definitions are compared in Fig. 2.
A clinical algorithm known as the AspICU criteria overcomes the limitations in the EORTC/ MSG criteria through the inclusion of an Aspergillus positive lower respiratory tract specimen culture  (39).Due to several studies describing 65% or lower sensitivity rates from lower respiratory tract specimen cultures (33), the AspICU criteria were further modified to define IPA (40).
With the emergence of IAPA, it was found that a subset of patients could not be classified through the EORTC/MSG or AspICU criteria due to the absence of defined host factors.Furthermore, patients with IAPA present with atypical pulmonary lesions.Through an expert group, a consensus case definition of IAPA was defined and fulfilled through an entry criterion based on host clinical features of influenza-like illness, detection of influenza virus and mycological evidence of Aspergillus or galactomannan in BAL, similar, to the currently used The European Organization for Research and Treatment of Cancer and the Mycoses Study For research purposes, the diagnosis of IPA is classified according to a scale of certainty (possible, probable or proven) based on imaging findings, serum biomarkers (beta-D-glucan, galactomannan and polymerase chain reaction [PCR] assays), sputum and/or BAL specimen for fungal culture, staining, galactomannan and/or PCR.As this classification is primarily research-orientated, one can make a diagnosis clinically without satisfying all criteria.The features of proven, probable and possible invasive fungal disease are summarized in Table 3.

Clinical and laboratory diagnosis of invasive aspergillosis
The diagnosis of invasive aspergillosis remains challenging.The EORTC/MSG definitions provide a useful tool for research and surveillance, but they are not intended for routine diagnosis in clinical practice.Use of these strict definitions could lead to under-detection.We review here some of the more commonly used diagnostic tools in the work-up of invasive aspergillosis.A comparison of the diagnostic accuracy of currently available laboratory tests including B-D-glucan, galactomannan and PCR tests can be found in Table 4.

Histopathology and culture
Examination of lung tissue remains the gold standard for diagnosing invasive pulmonary aspergillosis (IPA).The presence of septate, acute, branching hyphae invading lung tissue along with a culture positive for aspergillus from the same site is diagnostic of IPA (37).This tissue should be taken from a normally sterile site.Although aspergillus species can be readily cultured on most media, not all patients with invasive aspergillosis isolate the species.It is also important to note that aspergillus species can represent airway colonization in an immunocompetent host and therefore, does not always represent disease process.

Galactomannan antigen detection
Galactomannan is a polysaccharide that is a major constituent of aspergillus cell walls (43).It can be released into the blood and other bodily fluids in the early phase of aspergillus invasion, and its presence can be sustained for 1 to 8 weeks (44).The EORTC/MSG updated their guidelines in 2019 to include thresholds for different specimens (including plasma, serum, BAL or CSF).These include a single serum or plasma galactomannan level ≥1.0, BAL fluid ≥1.0, CSF ≥1.0 or a single serum/plasma ≥0.7 and BAL fluid ≥0.8.Results of ≥1.0 have been used in clinical trials in an aim to reduce the likelihood of false-positive results.Subsequent studies have suggested a cut-off of 0.5-0.7 provide relatively better performance and can be considered a positive result.
False-negative results can occur.Care must be utilized when interpreting results in patients receiving mould-active antifungal therapy as this can decrease the sensitivity of detecting galactomannan in serum (45).Other fungi species contain galactomannan on their cell walls, and therefore can cause false-positive results.Translocation of galactomannan in bacteria or foods across the intestinal mucosa may occur if there is impairment of mucosal integrity.This is especially significant in those who have undergone haematopoietic cell transplantation within the last 100 days and those with gastrointestinal graft-vs-host disease (46).

Beta-D-glucan
1,3-beta-D-glucan is a cell wall component of many fungi.It is not specific for aspergillus species and may be elevated in a variety of invasive fungal  (49).It can be detected early in the course of invasive fungal disease.In a meta-analysis of 16 studies that evaluated beta-D-glucan assays for the diagnosis of invasive fungal infections, it was found to have a sensitivity and specificity of 77% and 85%, respectively (48).
Its sensitivity and specificity are similar to that of galactomannan (Table 4) (50) though can vary depending on different assay type, underlying patient population and threshold for positivity.
There are many different assays currently available for serum detection; however, the current guidelines advise the use of Fungitell Ò .They

Sinonasal infection
• Imaging showing sinusitis plus one of the following three signs: nasal ulcer with black eschar, spread from the paranasal sinus across a bony barrier, acute localized pain

CNS infection
• One of the following; focal lesions on imaging and meningeal enhancement

Indirect tests
• Galactomannan antigen detected in plasma, serum, BAL fluid, CSF • Beta-D-glucan detected in serum •This refers to the presence of host factors and clinically features but in the absence of or with negative mycological findings.
suggest that a ß-D-glucan ≥80 ng/L detected in at least 2 consecutive serum samples is consistent with IPA, provided that other aetiologies have been excluded (38).However, this test comes with its own limitations and false-positive results can occur in patients receiving albumin, haemodialysis with cellulose membranes, intravenous immunoglobulin and intravenous amoxicillin-clavulanic acid.

Polymerase chain reaction
Polymerase chain reaction (PCR) can be performed on serum, plasma or BAL fluid.Diagnostic certainty increases with two consecutive positive results (51).When PCR tests are used, results should be considered within the clinical context and in conjunction with other diagnostic tools.The sensitivity of Aspergillus PCR in BAL fluid appears to be higher than with that of blood PCR but at the cost of a lower specificity (52).In 2009, a systematic review and meta-analysis investigated the use of PCR for diagnosis of IPA (48).Sixteen studies were included and samples from over 1618 patients at risk for invasive aspergillosis were taken.When two consecutive samples were required to define positivity, the sensitivity and specificity of PCR were 75% (95% CI 54-88%) and 87% (95% CI 78-93%), respectively.If a single positive test was required, these values were 88% (99% CI 75-94%) and 75% (99% CI 63-84%).It can be challenging to differentiate lung colonization with Aspergillus from active disease.

Imaging
The role of chest X-ray in diagnosing IPA is limited, as early signs are usually nonspecific.Use of chest computed tomography and high-resolution images early in the course aids diagnosis (53).Typical findings include multiple inflammatory nodules, often with a large dominant mass or a peripheral lesion.Early features include the halo sign.This is an area of low attenuation due to haemorrhage surrounding the pulmonary nodule.This tends to progress to cavitation or air crescent formation.This appears as a crescent-shaped lucency due to necrosis in the region of the original pulmonary nodule (54).While these signs are not pathognomonic for aspergillus, they can be a helpful clue in the appropriate clinical context.

MOLECULAR IMAGING
For in vivo detection of Aspergillus infection, studies have investigated the use of radiolabeled Aspergillus-specific monoclonal antibodies, and iron siderophobes in conjunction with PET/MR imaging (48).Thus far, studies have only been conducted in animal models.The humanized monoclonal antibody is currently undergoing toxicity testing prior to initiation of clinical trials.Molecular imaging of other human pathogens has been shown to be effective for species such as Fusarium, Scedosporium and Lomentospora.If successful, this could be a powerful tool to image and aid diagnose IPA (48).

TREATMENT
The overall approach to treatment of IPA involves early and definitive diagnosis, as well as early initiation of antifungal therapy (55).Surgery and immunomodulation may also have a role.

Antifungal agents
Primary treatment with a triazole antifungal agent such as voriconazole is recommended (55).Treatment of IPA with voriconazole was compared to amphotericin B deoxycholate in an international multicentre randomized trial in 2002 (56).It was found that initial therapy with voriconazole lead to better responses and improved survival, and resulted in fewer severe drug side effects when compared to Amphotericin B. On the basis of this trial, an initial treatment regime for voriconazole was derived; 6 mg/kg of body weight on Day 1, 4 mg/ kg twice daily for at least seven days, followed by 200 mg twice daily thereafter.Use of voriconazole requires monitoring of therapeutic levels to improve efficacy and avoid adverse effects.However, this can be problematic in the critically ill.Patients with critical illness frequently encounter hypoalbuminemia, capillary leakage syndrome, polypharmacy and continuous renal replacement therapy.

INVASIVE PULMONARY ASPERGILLOSIS IN THE ICU
All these factors can alter voriconazole plasma trough concentrations (57).The increase in azoleresistant Aspergillus isolates in recent years is also a growing cause for concern as it contributes to treatment failures in critically unwell patients (58).Primary treatment with other triazole antifungals, isavuconazole and posaconazole, has also been approved (59,60).However, itraconazole is not approved for first line use for IPA and therefore should not be used in immunocompromised patients.

Amphotericin B
Amphotericin B deoxycholate is a polyene class drug that is fungicidal.It has a number of significant side effects including severe nephrotoxicity.For this reason, it is not recommended.It is also not commercially available in every European country.Its lipid formulation which is associated with less tubular toxicity is therefore preferred (61,62).These include Liposomal amphotericin B (AmBisome) and Amphotericin B lipid complex (Abelcet).The primary advantage with these formulations is the ability to administer much larger doses with fewer systemic toxicities.AmBisome at an initial dose of 3 to 5 mg/kg body weight IV is generally recommended.Alternatively, Abelcet at a dose of 5 mg/kg IV daily is acceptable.Higher doses may be acceptable for central nervous system infections, less susceptible isolates and progressive infections.Doses of 10 mg/kg of AmBisome have been studied in the AmbiLoad trial, and although small observational studies have shown better response rates with higher doses, this randomized trial demonstrated higher rates of nephrotoxicity without additional therapeutic effect (63,64).However, amphotericin B may have a role in intensive care units where monitoring of voriconazole levels is not available.

Echinocandins
Echinocandins can be used in settings in which azole and polyene antifungals are contraindicated.Primary therapy for invasive pulmonary aspergillosis has not been recommended (65).Echinocandins include anidulafungin, caspofungin and micafungin.They can sometimes be considered for combination therapy (66).

Combination therapy
Combination antifungal therapy can be used for both initial therapy and as a strategy for those in whom initial therapy has failed (67).A combination of voriconazole and an echinocandin may be considered in select patients (55,66).A randomized control trial in which they assessed the efficacy of voriconazole treatment with or without 2 to 4 weeks of anidulafungin for the treatment of invasive aspergillosis in patients with haematological malignancies and/or HCT provides the strongest evidence for this approach.A trend toward improved survival in the combination group was seen but this was not statistically significant.However, when different diagnostic criteria were used for invasive aspergilloses in this study, combination therapy showed decreased mortality that was statistically significant.
Combination therapy with liposomal amphotericin B and an echinocandin has shown benefit in prospective studies, however to date there has been no randomized trial evidence to confirm this (68).There are also no clinical data to support the use of Amphotericin B and triazoles in combination therapy.

Duration of treatment
Treatment of IPA should be continued for a minimum of 6-12 weeks.This is largely dependent on the degree and duration of immunosuppression, site of disease and evidence of disease improvement (55).Antifungal therapy is usually continued until all signs and symptoms of the infection have resolved.Some immunosuppressed patients may continue treatment for months or even years.Adjustments can be made based on clinical response (66).

Immunomodulation
Where possible, immunosuppression should be reduced as an adjunct to antifungal therapy (55).Invasive aspergillus occurs most commonly in the setting of immunosuppression, particularly in those with neutropenia or prolonged steroid use.Recovery of bone marrow function in neutropenic patients is critical to recovery from IPA (69).Poor outcomes have been seen in those with persistent severe immune dysfunction.The use of colonystimulating factors may be considered in neutropenic patients; however, high quality evidence for this approach is still lacking.

Role of surgery
Surgery is recommended for single aspergillomas in order to prevent life-threatening haemorrhage or in cases of isolated disease for curative intent (70).In more complicated pulmonary disease, it is generally avoided.Chronic cavitatory pulmonary aspergillosis leads to very vascular and adherent pleura, making surgical resection challenging.There is also the risk of fungal spread to the residual pleural space leading to empyemas and/or bronchopleural fistulas (71).
In unilateral chronic cavitatory pulmonary aspergillosis, surgery may be preferred for those with drug intolerance or resistance to azoles.Pneumonectomy, however, is associated with a higher morbidity and mortality, especially if performed in emergency settings (55).

PROPHYLAXIS
Chemoprophylaxis to prevent invasive aspergillosis may be appropriate in certain patient cohorts including patients undergoing chemotherapy for acute myeloid leukaemia (AML) or myelodysplastic syndrome, patients with ≥2 weeks of neutropenia or with a history of IA pre-engraftment, patients with graft-vs-host disease (GVHD) after allogenic HSCT, solid organ transplant recipients and rare cases of inherited immunodeficiency (55).A summary of the recommendations can be found in Table 4 (72).Posaconazole has been found to be more effective than fluconazole or itraconazole for preventing aspergillosis in patients undergoing therapy for AML (73).It is also more effective than fluconazole in patients with GVHD after allogenic HSCT (74).Fluconazole is recommended in allogenic HSCT recipients until development of graftvs-host disease only.Inhaled liposomal amphotericin B has been studied and been found to reduce the incidence of aspergillosis in patients with haematological malignancies who had prolonged neutropenia (75).Based upon observational data, it is sometimes used in lung transplant recipients during the early posttransplant period.Voriconazole has been compared to fluconazole in prophylaxis against invasive fungal infections in haematological malignancies.There was a trend toward fewer infections in the voriconazole arm without being statistically significant (75).When considering prophylaxis, one must also take into account the potential toxicities and drug interactions that may occur for each patient (Table 5).
The value of prophylaxis in the setting of IAPA and CAPA remains more uncertain.A recently published randomized clinical trial of critically ill patients admitted to the ICU with respiratory failure due to influenza observed no significant reduction in the incidence of IAPA despite posaconazole prophylaxis (48).Higher mortality was reported in patients with early IAPA despite prompt diagnosis and initiation of antifungal therapy.With regard to CAPA, oral or intravenous posaconazole and inhaled amphotericin have been studied as antifungal prophylaxis without clear evidence of benefit.There was an attempted randomized controlled trial in 2021 to investigate the use of Isavuconazole in the prevention of CAPA (48).However, the trial was terminated early due to participant enrolment challenges (Isavu-CAPA Trial; ClinicalTrials.govID NCT04707703).

ONGOING AND FUTURE RESEARCH
In recent years, there has been a growing awareness of respiratory fungal diseases with the potential for major advances in their characterization and treatment as a consequence of post-genomic technologies which rationalize drug development and a path toward personalized medicines (76).
One study genetically engineered A. fumigatusspecific chimeric antigen receptor (Af-CAR) T cells and demonstrated their direct antifungal effect and ability to activate macrophages that augment the immune response against A. fumigatus in preclinical models in vitro and in vivo (77).More studies are needed to clinically evaluate the efficacy and safety of Af-CAR T cells for the treatment of IPA.
A number of new drug classes are now in late phase clinical studies, including Olorofim (F901318; F2G Ltd., Manchester, UK) which is the first of a new class of drugs, the orotomides, that inhibit dihydroorotate dehydrogenase, a key enzyme in pyrimidine synthesis (78).Olorofim is available orally and intravenously with wide tissue distribution.It has demonstrated activity against triazole-resistant strains.There is also an open label study ongoing to evaluate the utility of olorofim in individuals with limited treatment options (FORMULA; NTC03583164).Fosmanogepix (APX001; Amplyx, San Diego, CA, USA), is another novel antifungal agent with good activity in vitro against Aspergillus spp.(79) When metabolized to manogepix, its active form, disrupts glycosylphosphatidylinositol (GPI)-anchor biosynthesis by inhibiting the enzyme Gwt1.There is currently a phase 2, multicentre study to evaluate Fosmanogepix for the treatment of invasive fungal infections caused by Aspergillus spp. or rare moulds (e.g.Scedosporium spp., Fusarium spp.and mucoralean fungi).
There has also been increasing interest in the use of inhaled antifungal agents to achieve increased concentrations of drug in the respiratory mucosa compared to the systemic route and to minimize the systemic toxicity of oral or intravenous agents.PC945 (Pulmocide Ltd., London, UK) is a novel inhaled triazole that has potent activity against Aspergillus and accumulates in the lung on repeat dosing (80).Preclinical models indicated that it may be more effective when combined with systemic antifungals in murine pulmonary aspergillosis (81).Additional research is required to determine whether combination therapies are superior and in particular whether the combination of systemic and inhaled antifungals is superior to conventional systemic therapies that are currently prevalent.
Future studies are also needed to clarify what the host and risk factors for CAPA and IAPA are, whether newer treatments for COVID-19 and influenza impact on the risk of CAPA and IAPA, respectively, and whether there is a role for empirical antifungal therapy in sub-populations of COVID-19 or influenza.

CONCLUSIONS
Invasive aspergillosis is a growing phenomenon in critically ill patients in the intensive care unit, particularly affecting patients receiving systemic corticosteroids and those with underlying cardiorespiratory diseases or immunocompromise.However, it now also increasingly recognized among patients with mild immunosuppressive conditions or in apparently immunocompetent patients, such as those with severe influenza or COVID-19.Diagnosis can be challenging given the lack of consensus definition, the nonspecific clinical presentation and poor sensitivity of diagnostic assays.Equally, the treatment of pulmonary aspergillosis can be problematic because of the limited number of available antifungal drug classes and the emergence of resistance.However, the emergence of novel drug classes is promising for future disease management.

Ó
2023 The Authors.APMIS published by John Wiley & Sons Ltd on behalf of Scandinavian Societies for Pathology, Medical Microbiology and Immunology.657 INVASIVE PULMONARY ASPERGILLOSIS IN THE ICU as an alternative criterion for host factors

Table 1 .
Potential risk factors for the development of invasive pulmonary aspergillosis stratified by the degree of risk Ó 2023 The Authors.APMIS published by John Wiley & Sons Ltd on behalf of Scandinavian Societies for Pathology, Medical Microbiology and Immunology.

Table 2 .
Distinguishing features of IAPA and CAPA Fig. 2. Comparison of 2008 and 2022 criteria for probable invasive pulmonary aspergillosis based on EORTC/MSC guidelines.
Ó 2023 The Authors.APMIS published by John Wiley & Sons Ltd on behalf of Scandinavian Societies for Pathology, Medical Microbiology and

Table 3 .
Current diagnostic classification of invasive fungal disease according to a scale of certainty

Table 4 .
Comparison of the diagnostic accuracy of laboratory tests for invasive pulmonary aspergillosis based on key Ó 2023 The Authors.APMIS published by John Wiley & Sons Ltd on behalf of Scandinavian Societies for Pathology, Medical Microbiology and Immunology.

Table 5 .
Consensus Guidelines on antifungal prophylaxis against invasive aspergillus