SARS-CoV-2-Legionella Co-Infections: A Systematic Review and Meta-Analysis (2020-2021)

Severe Legionnaires' disease

BACKGROUND

Legionnaires' disease (LD) is a common but under-diagnosed cause of community-acquired pneumonia (CAP), although rapid detection of urine antigen testing (UAT) and advances in molecular testing have improved the diagnosis. LD entails intensive care unit (ICU) admission in almost one-third of cases, and the mortality rate ranges from 4% to 40%. This review aims to discuss recent advances in the study of this condition and to provide an update on the diagnosis, pathogenesis and management of severe LD.

RESULTS

The overall incidence of LD has increased worldwide in recent years due to the higher number of patients with risk factors, especially immunosuppression, and to improvements in diagnostic methods. Although LD is responsible for only around 5% of all-cause CAP, it is one of the three most common causes of CAP requiring ICU admission. Mortality in ICU patients, immunocompromised patients or patients with a nosocomial source of LD can reach 40% despite appropriate antimicrobial therapy. Regarding pathogenesis, no Legionella-specific virulence factors have been associated with severity; however, recent reports have found high pulmonary Legionella DNA loads, and impairments in immune response and lung microbiome in the most severe cases. The clinical picture includes severe lung injury requiring respiratory and/or hemodynamic support, extrapulmonary symptoms and non-specific laboratory findings. LD diagnostic methods have improved due to the broad use of UAT and the development of molecular methods allowing the detection of all Lp serogroups. Therapy is currently based on macrolides, quinolones, or a combination of the two, with prolonged treatment in severe cases.

CONCLUSIONS

Numerous factors influence the mortality rate of LD, such as ICU admission, the underlying immune status, and the nosocomial source of the infection. The host immune response (hyperinflammation and/or immunoparalysis) may also be associated with increased severity. Given that the incidence of LD is rising, studies on specific biomarkers of severity may be of great interest. Further assessments comparing different regimens and/or evaluating host-directed therapies are nowadays needed.

Herpesviridae and Atypical Bacteria Co-Detections in Lower Respiratory Tract Samples of SARS-CoV-2-Positive Patients Admitted to an Intensive Care Unit

Shortly after the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), cases of viral, bacterial, and fungal coinfections in hospitalized patients became evident. This retrospective study investigates the prevalence of multiple pathogen co-detections in 1472 lower respiratory tract (LRT) samples from 229 SARS-CoV-2-positive patients treated in the largest intensive care unit (ICU) in Slovenia. In addition to SARS-CoV-2, (rt)RT-PCR tests were used to detect cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes simplex virus 1 (HSV-1), herpes simplex virus 2 (HSV-2), varicella zoster virus (VZV), and atypical bacteria: Chlamydia pneumoniae, Mycoplasma pneumoniae and Legionella pneumophila/spp. At least one co-detection was observed in 89.1% of patients. EBV, HSV-1, and CMV were the most common, with 74.7%, 58.1%, and 38.0% of positive patients, respectively. The median detection time of EBV, HSV-1, and CMV after initial SARS-CoV-2 confirmation was 11 to 20 days. Bronchoalveolar lavage (BAL) and tracheal aspirate (TA) samples showed equivalent performance for the detection of EBV, CMV, and HSV-1 in patients with both available samples. Our results indicate that SARS-CoV-2 infection could be a risk factor for latent herpesvirus reactivation, especially HSV-1, EBV, and CMV. However, additional studies are needed to elucidate the clinical importance of these findings.

Editorial: Special Issue: "Legionella pneumophila: A Microorganism with a Thousand Faces"

Legionella pneumophila is a microorganism that is able to contaminate the freshwater environment and, consequently, human-made water systems [...].

Legionella pneumophila Rhizoferrin Promotes Bacterial Biofilm Formation and Growth within Amoebae and Macrophages

Previously, we showed that Legionella pneumophila secretes rhizoferrin, a polycarboxylate siderophore that promotes bacterial growth in iron-deplete media and the murine lung. Yet, past studies failed to identify a role for the rhizoferrin biosynthetic gene (lbtA) in L. pneumophila infection of host cells, suggesting the siderophore's importance was solely linked to extracellular survival. To test the possibility that rhizoferrin's relevance to intracellular infection was missed due to functional redundancy with the ferrous iron transport (FeoB) pathway, we characterized a new mutant lacking both lbtA and feoB. This mutant was highly impaired for growth on bacteriological media that were only modestly depleted of iron, confirming that rhizoferrin-mediated ferric iron uptake and FeoB-mediated ferrous iron uptake are critical for iron acquisition. The lbtA feoB mutant, but not its lbtA-containing complement, was also highly defective for biofilm formation on plastic surfaces, demonstrating a new role for the L. pneumophila siderophore in extracellular survival. Finally, the lbtA feoB mutant, but not its complement containing lbtA, proved to be greatly impaired for growth in Acanthamoeba castellanii, Vermamoeba vermiformis, and human U937 cell macrophages, revealing that rhizoferrin does promote intracellular infection by L. pneumophila. Moreover, the application of purified rhizoferrin triggered cytokine production from the U937 cells. Rhizoferrin-associated genes were fully conserved across the many sequenced strains of L. pneumophila examined but were variably present among strains from the other species of Legionella. Outside of Legionella, the closest match to the L. pneumophila rhizoferrin genes was in Aquicella siphonis, another facultative intracellular parasite of amoebae.

Legionnaires' Disease in Occupational Settings: A Cross-Sectional Study from Northeastern Italy (2019)

In Italy, Legionnaires' Disease (LD) causes >1000 hospital admissions per year, with a lethality rate of 5 to 10%. Occupational exposures could reasonably explain a substantial share of total cases, but the role of Occupational Physicians (OPs) in management and prevention of LD has been scarcely investigated. The present survey therefore evaluates the knowledge, attitudes and practices (KAP) regarding LD from a convenience sample of Italian OPs, focusing on their participation in preventive interventions. A total of 165 OPs were recruited through a training event (Parma, Northeastern Italy, 2019), and completed a specifically designed structured questionnaire. The association between reported participation in preventive interventions and individual factors was analyzed using a binary logistic regression model, calculating corresponding multivariable Odds Ratio (aOR). Overall, participants exhibited satisfactory knowledge of the clinical and diagnostic aspects of LD, while substantial uncertainties were associated epidemiological factors (i.e., notification rate and lethality). Although the majority of participating OPs reportedly assisted at least one hospital (26.7%) and/or a nursing home (42.4%) and/or a wastewater treatment plant, only 41.8% reportedly contributed to the risk assessment for LD and 18.8% promoted specifically designed preventive measures. Working as OPs in nursing homes (aOR 8.732; 95% Confidence Intervals [95%CI] 2.991 to 25.487) and wastewater treatment plants (aOR 8.710; 95%CI 2.844 to 26.668) was associated with participation in the risk assessment for LD, while the promotion of preventive practice was associated with working as an OP in hospitals (aOR 6.792; 95%CI 2.026 to 22.764) and wastewater treatment plants (aOR 4.464, 95%CI 1.363 to 14.619). In other words, the effective participation of the OP in the implementation of preventive measures appears uncommon and is limited to certain occupational settings. Collectively, these results highlight the importance of tailoring specifically designed information campaigns aimed to raise the involvement of OPs in the prevention of LD in occupational settings other than healthcare.

Legionellosis-Associated Hospitalization in Spain from 2002 to 2021

Legionellosis is a respiratory disease of bacterial and environmental origin that usually presents two distinct clinical entities, "Legionnaires' disease" (LD) and "Pontiac fever". LD is an important cause of hospital-acquired pneumonia (HAP). The objective of this study is to describe the epidemiology of legionellosis-associated hospitalization (L-AH) in Spain from 2002 to 2021 and the burden of hospitalization due to legionellosis. Discharge reports from the Minimum Basic Data Set (MBDS) were used to retrospectively analyze hospital discharge data with a diagnosis of legionellosis, based on the ICD-9-CM and ICD-10-CM diagnosis codes, from 2002 to 2021. 21,300 L-AH occurred throughout the year during 2002-2021. The incidence of hospitalization associated per 100,000 inhabitants by month showed a similar trend for the 2002-2011, 2012-2021, and 2002-2021 periods. In Spain, during 2002-2021, the hospitalization rate (HR) in the autonomous communities ranged from 4.57 (2002-2011) to 0.24 (2012-2021) cases per 100,000 inhabitants. The HR of legionellosis in Spain has substantially increased across the 2002-2021 period, and the estimate is consistent with available European data. It is considered that in-depth epidemiological surveillance studies of legionellosis and improvements in the prevention and control of the disease are required in Spain.

Risk Factors of Severe COVID-19: A Review of Host, Viral and Environmental Factors

The clinical course and outcome of COVID-19 are highly variable, ranging from asymptomatic infections to severe disease and death. Understanding the risk factors of severe COVID-19 is relevant both in the clinical setting and at the epidemiological level. Here, we provide an overview of host, viral and environmental factors that have been shown or (in some cases) hypothesized to be associated with severe clinical outcomes. The factors considered in detail include the age and frailty, genetic polymorphisms, biological sex (and pregnancy), co- and superinfections, non-communicable comorbidities, immunological history, microbiota, and lifestyle of the patient; viral genetic variation and infecting dose; socioeconomic factors; and air pollution. For each category, we compile (sometimes conflicting) evidence for the association of the factor with COVID-19 outcomes (including the strength of the effect) and outline possible action mechanisms. We also discuss the complex interactions between the various risk factors.

A Patient with Concurrent Legionella and COVID-19 Infection in a UK District General Hospital

A 65 year-old gentleman had been brought to our Respiratory Emergency Department for patients with respiratory symptoms and a possible COVID-19 infection with a 3-day history of shortness of breath (SOB), fever, a productive cough of yellow sputum, and right-sided chest pain. The patient had received both vaccinations at the time and initially reported no travel history, although later it was revealed that he had recently stayed at a hotel. He tested positive for COVID-19 and had hyponatremia and a raised procalcitonin, indicating a bacterial infection as well. He had been initiated on our local treatment guidelines for COVID with antibiotics, guided by local hospital guidelines. An atypical pneumonia screen returned a positive result for Legionella urine antigen, and his antibiotic regime was changed accordingly. Our patient deteriorated significantly, and despite being escalated to our intensive care unit (ICU), he unfortunately passed away. Our case highlights the importance of early ICU involvement and escalation of antibiotics in cases of suspected concurrent Legionella and COVID-19 infections.

Legionella pneumophila Cas2 Promotes the Expression of Small Heat Shock Protein C2 That Is Required for Thermal Tolerance and Optimal Intracellular Infection

Previously, we demonstrated that Cas2 encoded within the CRISPR-Cas locus of Legionella pneumophila strain 130b promotes the ability of the Legionella pathogen to infect amoebal hosts. Given that L. pneumophila Cas2 has RNase activity, we posited that the cytoplasmic protein is regulating the expression of another Legionella gene(s) that fosters intracellular infection. Proteomics revealed 10 proteins at diminished levels in the cas2 mutant, and reverse transcription-quantitative (qRT-PCR) confirmed the reduced expression of a gene encoding putative small heat shock protein C2 (HspC2), among several others. As predicted, the gene was expressed more highly at 37°C to 50°C than that at 30°C, and an hspC2 mutant, but not its complemented derivative, displayed ~100-fold reduced CFU following heat shock at 55°C. Compatible with the effect of Cas2 on hspC2 expression, strains lacking Cas2 also had impaired thermal tolerance. The hspC2 mutant, like the cas2 mutant before it, was greatly impaired for infection of Acanthamoeba castellanii, a frequent host for legionellae in waters. HspC2 and Cas2 were not required for entry into these host cells but promoted the replicative phase of intracellular infection. Finally, the hspC2 mutant exhibited an additional defect during the infection of macrophages, which are the primary host for legionellae during lung infection. In summary, hspC2 is upregulated by the presence of Cas2, and HspC2 uniquely promotes both L. pneumophila extracellular survival at high temperatures and infection of amoebal and human host cells. To our knowledge, these findings also represent the first genetic proof linking Cas2 to thermotolerance, expanding the repertoire of noncanonical functions associated with CRISPR-Cas proteins.