Introduction
Coronavirus is a family of RNA viruses that can cause of common cold, Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) with the mortality rate of 10% and 37%, respectively (1). The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel coronavirus, that causes coronavirus disease 2019 (COVID-19) was discovered in Wuhan, China and expanded in all over the world from 31 December and spread across the continents (2, 3). The earliest countries (China, South Korea, and Iran) announced the COVID-19 outbreak as a public health problem(4).
The coronavirus’s 3000 nucleotide genome encodes four structural protein such as, Spike (S) protein, Nucleocapsid (N) protein, Membrane (M) protein, envelop (E) protein and several non-structural proteins (nsp) (5). Spike (S) protein consist of transmembrane (TM) domain which is able to bind a host receptor. Nuclear capsid or N-protein which is bound to the virus single positive strand RNA, is located inside in the capsid. Nucleoprotein gene plays key role in virus’s replication and transcription; it allows the virus to hijack human cells and turn them into virus factories (6). M protein is the most abundant protein in the viral surfaces which is the central organizer for the virus protein. The E-protein is a small membrane protein, plays an important role in virus assembly subunits, membrane penetrance of the host cell and interaction between viruses and host cells (7).
The symptoms of COVID-19 can include fever, cough, sore throat, fatigue, shortness of breath and gastrointestinal symptoms such as diarrhea and nausea (8, 9). Coronaviruses have been responsible for the common cold by a long time and it is reported that the symptoms of SARS-CoV-2 disease in human is similar to the common cold or influenza; but the infection and mortality rate of the SARS-CoV-2 is higher than other respiratory infections. SARS-CoV-2 is a contiguous virus and can be transmit by the infected person breathed, coughed, or sneezed (10). Study shows that SARS-CoV-2 may have co-infection with other pathogens such as viruses, bacteria, and fungi which are related to increase in hospitalization rate and mortality. It is reported that the most co-infection occur with influenza virus (11). Influenza is a respiratory illness with the sign of fever, chills, body aches, sore throats, nasal congestion, fatigue, vomiting, abdominal pain, and diarrhea, and seems to have similar transmission character with COVID-19 (12, 13). Recently study have clarified that there are Immunopathological similarities between influenza and SARS-CoV-2 (14). Several studies from United Sate of America (15, 16), china (17) and Iran (18) show that there is co-infection with SARS-CoV-2 and influenza A and B virus. In addition some researches indicate that the co-infection of SARS-CoV-2 with influenza in patients suffering from pneumonia, sinus infection, bronchitis and cardiovascular disease (CVD) promote the mortality rate (18-20).
Researchers found that patients admitted to hospital with COVID-19 also infected with influenza virus. Thus, the current research provides a better understanding about the control and treatment of co-infection with SARS-CoV-2 and the influenza virus. So, This study aims to assess the co-infection of SARS-CoV-2 with influenza among COVID-19 cases.