# Deep Learning System for COVID-19 Diagnosis Aid Using X-ray Pulmonary Images
## 1 Introduction  
Coronaviruses are enveloped, unsegmented, and positive-sense single-stranded RNA viruses. Six species of coronavirus are known to cause disease in humans, most of them generally cause mild respiratory disease; however, fatal coronaviruses have periodically emerged in recent decades, such as the 2002 Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and the Middle East Respiratory Syndrome Coronavirus in 2012. In December 2019, the Office of the World Health Organization in China was informed of cases of pneumonia of unknown etiology detected in Wuhan, and a new coronavirus, called SARS-CoV-2, was extracted from samples of the lower respiratory tract of several patients [1]. Since then, until June 1 st of 2020, more than 6.18 million cases have been confirmed worldwide, and the infection has spread to many countries around the world. USA has the highest rate in America with more than 1.79 million cases and more than 104,000 deaths. In Europe, Spain has one of the highest rates with more than 239,000 confirmed infections and more that 27,000 deaths [2]. On March 11 th of 2020, the World Health Organization (WHO) declared the infection as a pandemic and, since then, several countries have applied restriction measures to their population in order to reduce the spread of the disease [3]. The most common symptoms of the disease related to SARS-CoV-2, called Coronavirus Disease 2019 or COVID-19 by WHO on Feb 11 th of 2020, are fever, weakness, cough, and diarrhea. More thanhalf of patients report shortness of breath and few develop acute respiratory distress syndrome. After septic shock, refractory metabolic acidosis and coagulation dysfunction can lead to death, with a fatality rate about 6% worldwide [4]. Some countries has a higher death rate, like United Kingdom and Italy with a value around 14%, and Spain with a 11.3%. Person-to-person transmission occurs primarily through direct contact or air drops. The highest risk of transmission is within about 1 meter of the infected person; however, the maximum distance is still undetermined [5]. Most countries are using a huge amount of clinical and epidemiologic information to determine who should be tested. According to empirical studies like Reference [6] or Reference [7], most patients with confirmed COVID-19 develop fever and/or symptoms of acute respiratory illness (like cough or difficulty breathing). If a person is under investigation, it is recommended that practitioners immediately put in place infection control and prevention measures. The first recommendation is testing for all other sources of respiratory infection (to exclude COVID-19). Moreover, in order to assist in the decision making process and to determine who to test, some epidemiologic factors are recommended to be used. These factors include anyone who has had close contact with a patient with laboratory-confirmed COVID-19 within 14 days of symptom onset or a history of travel from affected geographic areas [8]. Once, these factors determine that testing should be done, the WHO recommends collecting specimens from both the upper respiratory tract (naso and oropharyngeal samples) and lower respiratory tract such as expectorated sputum, endotracheal aspirate, or Bronchoalveolar Lavage (BAL) [9]; but the collection of BAL samples should only be performed in mechanically ventilated patients as lower respiratory tract samples seem to remain positive for a more extended period. All the samples require storage at four degrees celsius. In the laboratory, the amplification of the genetic material extracted from the saliva and/or mucus samples are carried out through a Reverse Transcription Polymerase Chain Reaction (RT-PCR), which involves the synthesis of a double-stranded DNA molecule from an RNA mold [10]. Once the genetic material is enough, the search is done for those portions of the genetic code of the COVID-19 that are conserved.