## 4 Discussion  
In December 2019, the novel coronavirus emerged in Wuhan, the capital city of Hubei, China. The enveloped RNA betacoronavirus has been soon named SARS-CoV-2 due to its phylogenetic similarity to SARS-CoV [9, 10, 11, 12]. On February 20, 2020, the first case of the novel COVID-19 was detected in Italy, and 20 days later, WHO declared the COVID-19 outbreak a global pandemic [13, 14, 15, 16]. Italy had one of the highest rates of SARS-CoV-2 infection worldwide, with 3044 cases per 100,000 people, as well as the second-highest mortality rate, 13.4% vs. an average value of 6.9% (as of 22 April 2020; [[https://coronavirus.jhu.edu/map.html](https://coronavirus.jhu.edu/map.html)]([https://coronavirus.jhu.edu/map.html](https://coronavirus.jhu.edu/map.html)) (accessed on 13 th February 2020)). The Lombardy region, with 10.6 million people living in highly populated areas, has been the epicenter of the infection, with 37.4% of total cases registered in the country and more than 50% of the total number of deaths ([[http://www.salute.gov.it](http://www.salute.gov.it)]([http://www.salute.gov.it](http://www.salute.gov.it)) (accessed on 13 th February 2020)) [17, 18, 19]. The disarming rate of mortality was not only related to severe pneumonia but also highly influenced by the COVID-19 multiorgan involvement [20]. Comorbidities, cardiovascular complications, renal or liver failure, hyperinflammatory response, acute shock, and neurological sequelae are to be considered as the most insidious and unpredictable aspect of the pandemic [21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38].  
The overall condition of the north of Italy was further worsened by the unpreparedness of the health system, as in most of the world. This tragic scenario imposed the need to put in practice a management algorithm able to counteract the spreading of the infection, concurrently fighting against the time. In light of these assumptions and as for other diseases in the field of emergency medicine, a practiced, feasible, fast, and effective organizational model was urgently need, especially in the ED [39, 40, 41, 42, 43, 44, 45, 46, 47, 48].  
At the ED of the Humanitas Clinical and Research Center, we applied, soon after the declaration of the pandemic, the Lean model. As evidenced by the literature, the implementation of Lean offers tremendous opportunities in the ED to improve the overcrowding, costs, and time-wasting, compared to traditional models [49, 50, 51, 52, 53, 54, 55].  
In 2009, [PERSON] and colleagues evaluated the application of the Lean method in the ED and demonstrated the decrease in length of hospital stay and increase in improvement of patient visits [56]. In 2011, [PERSON] et al. overviewed the application of the Lean model in several American, Australian, and Canadian hospitals, revealing its organizational success [57]. [PERSON] and his group, in November 2015, put in practice the Lean method in the ED of Cardarelli Hospital in Naples. Data acquired revealed the effectiveness of this strategy in cost containment and patient safety [58]. More recently, in 2021, [PERSON] et al. performed a review about the application of Lean techniques in ED, also with the aim to improve the quality of treatment [59].  
In accordance with literature results, applied to our ED, the Lean approach appears to reduce errors and waiting time leading to an improvement in the quality of care for the patients. It was defined for patients and health professionals, prioritizing the wellbeing of both and ensuring secure, linear, and shared processes. The proposed model had extremely positive impacts during the outbreak and stands out as one of the few studies on lean adoption in ED to face and re-organize patients' admissions during the COVID-19 outbreak. Additionally, this work contributes to promoting an algorithm in which lean is integrated using a multidisciplinary approach [2].