COVID-19 and influenza co-infection
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. ; Associate Editor(s)-in-Chief: Zaida Obeidat, M.D.
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.
- The risk of complications in Influenza for young healthy children are higher compared to COVID-19.
- Infants and children with underlying medical conditions are at the highest risk for both Influenza and COVID-19.
|Treatment||- Supportive medical care to relieve symptoms and complications.||
- The National Institute of Health (NIH) has developed guidance on treatment, which will be updated regularly as new evidence on safety and efficacy of drugs come out.
- There are no drugs approved by the FDA to prevent or treat COVID-19.
- Remdesivir (antiviral agent) is available under Emergency Use Authorization (EUA), and being explored as a treatment for 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.
- There is no Vaccine to COVID-19 yet but researchers and vaccine developers are working on developing a vaccine to prevent COVID-19.
- 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:
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:
- Immunocompromised ( e.g. chronic infections or cancer patients).
- It's more common among the workers who works in close contact.
- It's common among the population who doesn't maintain proper social distancing.
- 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. 
- SARS-CoV-2 and Influenza co-infection did not significantly worsen the symptoms and outcomes. 
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 X-ray images showing bilateral/peripheral opacities with lower lobes predominant.
- 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".
- ↑ Wu X, Cai Y, Huang X, Yu X, Zhao L, Wang F; et al. (2020). "Co-infection with SARS-CoV-2 and Influenza A Virus in Patient with Pneumonia, China". Emerg Infect Dis. 26 (6): 1324–1326. doi:10.3201/eid2606.200299. PMC 7258479 Check
|pmc=value (help). PMID 32160148 Check
- ↑ 3.0 3.1 Kondo Y, Miyazaki S, Yamashita R, Ikeda T (2020). "Coinfection with SARS-CoV-2 and influenza A virus". BMJ Case Rep. 13 (7). doi:10.1136/bcr-2020-236812. PMC 7358105 Check
|pmc=value (help). PMID 32611659 Check
- ↑ 4.0 4.1 Konala VM, Adapa S, Gayam V, Naramala S, Daggubati SR, Kammari CB; et al. (2020). "Co-infection with Influenza A and COVID-19". Eur J Case Rep Intern Med. 7 (5): 001656. doi:10.12890/2020_001656. PMC 7213830 Check
|pmc=value (help). PMID 32399452 Check
- ↑ Lönnroth K, Jaramillo E, Williams BG, Dye C, Raviglione M (2009). "Drivers of tuberculosis epidemics: the role of risk factors and social determinants". Soc Sci Med. 68 (12): 2240–6. doi:10.1016/j.socscimed.2009.03.041. PMID 19394122.
- ↑ 6.0 6.1 6.2 Lyon SM, Rossman MD (2017). "Pulmonary Tuberculosis". Microbiol Spectr. 5 (1). doi:10.1128/microbiolspec.TNMI7-0032-2016. PMID 28185620.
- ↑ Sevilla DC, Wagner NB, Anderson WD, Ideker RE, Reimer KA, Mikat EM; et al. (1990). "Sensitivity of a set of myocardial infarction screening criteria in patients with anatomically documented single and multiple infarcts". Am J Cardiol. 66 (10): 792–5. doi:10.1016/0002-9149(90)90353-3. PMID 2220574.
- ↑ 8.0 8.1 8.2 8.3 Ding Q, Lu P, Fan Y, Xia Y, Liu M (2020). "The clinical characteristics of pneumonia patients coinfected with 2019 novel coronavirus and influenza virus in Wuhan, China". J Med Virol. doi:10.1002/jmv.25781. PMC 7228290 Check
|pmc=value (help). PMID 32196707 Check
- ↑ 9.0 9.1 9.2 Konala VM, Adapa S, Naramala S, Chenna A, Lamichhane S, Garlapati PR; et al. (2020). "A Case Series of Patients Coinfected With Influenza and COVID-19". J Investig Med High Impact Case Rep. 8: 2324709620934674. doi:10.1177/2324709620934674. PMC 7290261 Check
|pmc=value (help). PMID 32522037 Check
- ↑ Hsih WH, Cheng MY, Ho MW, Chou CH, Lin PC, Chi CY; et al. (2020). "Featuring COVID-19 cases via screening symptomatic patients with epidemiologic link during flu season in a medical center of central Taiwan". J Microbiol Immunol Infect. 53 (3): 459–466. doi:10.1016/j.jmii.2020.03.008. PMC 7102665 Check
|pmc=value (help). PMID 32220574 : 32220574 Check
- ↑ Cuadrado-Payán E, Montagud-Marrahi E, Torres-Elorza M, Bodro M, Blasco M, Poch E; et al. (2020). "SARS-CoV-2 and influenza virus co-infection". Lancet. 395 (10236): e84. doi:10.1016/S0140-6736(20)31052-7. PMC 7200126 Check
|pmc=value (help). PMID 32423586 Check
- ↑ Yin S, Peng Y, Ren Y, Hu M, Tang L, Xiang Z; et al. (2020). "The implications of preliminary screening and diagnosis: Clinical characteristics of 33 mild patients with SARS-CoV-2 infection in Hunan, China". J Clin Virol. 128: 104397. doi:10.1016/j.jcv.2020.104397. PMC 7192082 Check
|pmc=value (help). PMID 32388472 Check
- ↑ 13.0 13.1 13.2 D'Abramo A, Lepore L, Palazzolo C, Barreca F, Liuzzi G, Lalle E; et al. (2020). "Acute respiratory distress syndrome due to SARS-CoV-2 and Influenza A co-infection in an Italian patient: Mini-review of the literature". Int J Infect Dis. 97: 236–239. doi:10.1016/j.ijid.2020.06.056. PMC 7301795 Check
|pmc=value (help). PMID 32565366 Check
- ↑ 14.0 14.1 Awadasseid A, Wu Y, Tanaka Y, Zhang W (2020). "Initial success in the identification and management of the coronavirus disease 2019 (COVID-19) indicates human-to-human transmission in Wuhan, China". Int J Biol Sci. 16 (11): 1846–1860. doi:10.7150/ijbs.45018. PMC 7211182 Check
|pmc=value (help). PMID 32398954 Check
- ↑ Azekawa S, Namkoong H, Mitamura K, Kawaoka Y, Saito F (2020). "Co-infection with SARS-CoV-2 and influenza A virus". IDCases. 20: e00775. doi:10.1016/j.idcr.2020.e00775. PMC 7184249 Check
|pmc=value (help). PMID 32368495 Check
- ↑ Schwartz L, Atlas D (1989). "Synergy between membrane depolarization and muscarinic receptor activation leads to potentiation of neurotransmitter release (II)". Brain Res. 503 (1): 62–7. doi:10.1016/0006-8993(89)91704-6. PMID 2611659.