COVID-19 and influenza co-infection
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For COVID-19 frequently asked inpatient questions, click here
For COVID-19 frequently asked outpatient questions, click here
Synonyms and Keywords:
In December 2019, a novel coronavirus, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was identified as the cause of an outbreak of acute respiratory illness in Wuhan, China. Since then, there has been a rapid spread of the virus, leading to a global pandemic of coronavirus disease 2019 (COVID-19). Influenza, commonly known as flu, is an infectious disease of birds and mammals caused by RNA viruses of the biological family Orthomyxoviridae (the influenza viruses). Coronavirus disease 2019 (COVID-19) and Influenza share many characteristics, common symptoms of the co-infection are fever, sore throat, dyspnea, myalgia, cough, headache, fatigue and malaise.   
- COVID-19, also called severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) originated in Wuhan, China in late December 2019.
- It has been declared a global pandemic by the WHO after being caused a significant morbidity and mortality worldwide.
- Influenza is a highly contagious respiratory virus, it causes an acute respiratory infection, occurs mainly during the winter, it causes significant morbidity and mortality worldwide.
- It can be mild or sever, which may result in hospitalization or death.
- People at high risk of serious complications are young children, elderly, and people with underlying medical conditions.
- The total number of morbidity and mortality has been declining significantly after the seasonal Influenza vaccine. 
- The exact pathogenesis of co-infection with SARS-CoV-2 and Influenza viruses is not fully understood.
- Coronavirus disease 2019 (COVID-19) and Influenza co-infection are caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza (A or B) virus.
Differentiating COVID-19 and Influenza co-infection from other Diseases
- Influenza and COVID-19 are both contagious respiratory illnesses, but they are caused by different viruses.
- Influenza is caused by infection with influenza viruses and COVID-19 is caused by infection with the coronavirus2 (SARS-CoV-2).
- Testing may be needed to help confirm a diagnosis because some of the symptoms of flu and COVID-19 are similar.
- Influenza and COVID-19 share many characteristics, but there are some key differences between the two.
|This table compares the Influenza and COVID-19: "Similarities and Differences between Flu and COVID-19 | CDC".|
|Similarities between Covid-19 and Influenza infection||Differences between Covid-19 and Influenza infection|
|Signs and symptoms||
|Period of Contagiousness||
|How does it spread||
|High risk groups||
- People with underlying medical conditions.
- Pregnant[ women.
|- School-aged children infected with COVID-19 are at higher risk of Multisystem Inflammatory Syndrome in Children (MIS-C) which is rare but sever complication.|
|Treatment||- Supportive medical care to relieve symptoms and complications.||
- There are no drugs approved by the FDA to prevent or treat COVID-19.
- Hospitalized patients with Influenza or high risk group are recommended to be treated with antiviral drugs.
|Vaccine||- Vaccines for COVID-19 and Influenza must be approved by the FDA.||- There are multiple vaccines to protect against 3 or 4 viruses that cause the Influenza produced annually and approved by the FDA.|
- Coronavirus disease 2019 (COVID-19) and Influenza co-infection, must be differentiated from other diseases that may cause fever, cough, shortness of breath and tachypnea. The table below, summarizes the differential diagnosis:
|Diseases||Past medical history||Symptoms||Physical Examination||Diagnostic tests||Other Findings|
|Headache||Chest pain||Wheezing||Dyspnea||Chest Tenderness||Cough||Hemoptysis||Fever||Tachypnea||Tachycardia||CT/MRI||Chest X-ray|
|COVID-19 and Influenza co-infection||
|Chronic obstructive pulmonary disease (COPD)||-||-||+||+||-||+||-||-||+||+||
Epidemiology and Demographics
- Patients of all age groups may develop COVID-19 and influenza co-infection.
- The countries that got affected by the pandemic are:
- The United States
- Common risk factors in the development of COVID-19 and influenza infection include:
- To view the COVID-19 risk factors, click here.
- There is insufficient evidence to recommend routine screening for COVID-19 and Influenza co-infection.
- For the prevention and control of infection, on January 24th 2020 Taiwan Centers for Disease Control started testing of SARS-CoV-2 for people suspected with COVID-19. Until February 28th, 2015 cases were screened and 34 of them were diagnosed of COVID-19. During this time, 43 flu-like symptomatic patients were screened in China Medical University Hospital and 2 of them were confirmed to be positive for SARS-CoV-2. 
- To establish the diagnostic protocol for the co-infection of COVID-19 and other respiratory infections like Influenza A and B, they comparatively analyzed the clinical presentations, laboratory data, radiologic findings, and travel and exposure contact histories, of COVID-19 patients who suspected to have other respiratory infections.
- SARS-CoV-2 detection by real-time reverse transcription polymerase chain reaction (rRT-PCR) and Respiratory pathogens detection by FilmArray™ Respiratory Panel were used for screening.
Natural History, Complications, and Prognosis
- SARS-CoV-2 and Influenza co-infection has a wide range of clinical presentation, most of the symptoms are similar, the symptoms can be vary from asymptomatic to severe disease (ARDS) which require the ICU admission.
- The main complications for the patients according to a study conducted in Wuhan, China, were acute respiratory distress syndrome, acute liver injury, and diarrhea. 
Diagnostic Study of Choice
- The diagnosis of COVID-19 and Influenza co-infection can be established by the following investigations: 
- SARS-CoV-2 detection by real-time reverse transcription polymerase chain reaction (rRT-PCR) from nasopharyngeal swab sample or bronchoalveolar lavage fluid.
- Respiratory pathogens detection by FilmArray™ Respiratory Panel. 
- Rapid nucleic acid amplification test for influenza A and B.
- Chest Tomography images showing peripheral and bilateral multiple plaques or nodular ground-glass opacities.
- According to a study conducted in Wuhan, China, common symptoms at onset of illness included:   
- Common physical examination findings of the co-infection with COVID-19 and Influenza include: fever, dry cough, tachypnea, and tachycardia.
- Decrease in oxygen saturation SpO2(< 93%), the first manifestation of deterioration of inflammatory lung injury.
Common laboratory findings associated with covid-19 and influenza coinfection are:
- Lymphocytopenia (80% of patients)
- Elevated liver functions AST, ALT (40%)
- Elevated CRP (80%)
- Elevated ESR (30%)
- Elevated BUN (30%)
- Elevated Creatinine (70%)
- Elevated ferritin (70%)
- Elevated fibrinogen
- Elevated D-dimer
- Elevated interleukin-6
- Elevated lactic acid
- Elevated LDH
- Elevated creatine kinase    
- Chest Tomography images showing peripheral and bilateral ground-glass consolidation peripherally.    
- There is no treatment available for COVID-19, the mainstay of therapy is supportive care.
- Hydroxychloroquine, azithromycin, Interferon-l, glucocorticoids, interleukin antagonists, Ulinastatin, intravenous immunoglobulins, and plasmapheresis are already used in clinical practice for COVID-19 and showed initial positive outcomes. 
- The National Institutes of Health (NIH) COVID-19 treatment guidelines recommend Remdesivir for hospitalised patients with severe COVID-19. 
- Severe disease require intubation and mechanical ventilation.
- Dexamthasone is helpful in hospitalized and oxygen dependent patients with COVID-19.
- Antiviral agents (Oseltamivir, Zanamivir, Peramivir, and Baloxavir) are recommended by the CDC for all hospitalized and high risk patients with Influenza.
- The CDC recommends getting the Influenza vaccine, there are multiple FDA-licensed influenza vaccines produced annually to protect against the 3 or 4 influenza viruses.
- There is currently no vaccine to prevent COVID-19. The best way to prevent infection is to avoid being exposed to the virus by:
- Washing hands regularly with soap and water for at least 20 seconds or using a hand sanitizer with 60% alcohol.
- Wearing a cloth face mask and avoid touching eyes, nose, and mouth with unwashed hands.
- Covering mouth and nose when cough or sneeze.
- Maintaining 6 feet distance from other people and avoiding close contact.
- Refraining smoking and other activities that weaken the lungs.
- Clean and disinfect frequently touched surfaces and objects.
- There are no secondary prevention measures of COVID-19 and Influenza co-infection.
- The secondary prevention measures of COVID-19 include measures to make sure that an infected individual does not transfer the disease to others.
- WHO recommends for patients with suspected or confirmed COVID-19 with mild symptoms to stay home and self isolation from other family members at home.
- To read more about COVID-19 secondary prevention, Click here.
- Merck Manual Home Edition. "Influenza: Viral Infections".
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