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Case report

COVID-19 and Influenza Co-Infection: Report of Three Cases


Influenza and coronavirus disease 2019 (COVID-19) are both contagious respiratory illnesses, but they are caused by different viruses. COVID-19 pandemic is caused by a novel virus - severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Influenza is an infectious respiratory disease, caused by influenza A and influenza B viruses. We describe the three cases of influenza and COVID-19 co-infection.


Coronavirus disease 2019 (COVID-19) originated in the Huanan South China Seafood Market in Wuhan. It has posed a global health threat. COVID-19 can present with a spectrum of clinical manifestations including fever, myalgia, cough, dyspnea, and less frequently headache, diarrhea, nausea, and vomiting. Although respiratory symptoms predominate, multiple organ dysfunction may also occur with COVID-19. Coagulopathy has been found as a prominent feature of COVID-19 and severe coagulation dysfunction may be associated with poor prognosis [1-3]. Neurological and cardiovascular complications are also common in COVID-19 patients. No effective treatment has yet been established.

Case Presentation

The mean age was 59.6 years (range 47-71 years) and 2/3 were female. Two were Hispanic and one was Pilipino. Comorbidities included hypertension and diabetes mellitus. COVID-19 was diagnosed by nasopharyngeal swab reverse-transcription polymerase chain reaction (RT-PCR) and influenza by rapid antigen assay. Two patients had influenza type B and one had influenza type A. The presenting sign and symptoms were cough, fever, shortness of breath and myalgia. Chest X-ray (CXR) and computed tomography (CT) of the case 1 and case 2 are shown in Figure 1A-1D.

CXR of the case 3 is shown in Figure 2.

One patient (case 2) had positive blood culture for Enterococcus faecium. Two patients required intubation during their hospital course. Inflammatory markers (ESR, CRP, IL-6) were elevated in the patients. All three patients were treated with hydroxychloroquine, azithromycin, ceftriaxone for COVID-19 and Oseltamivir for influenza. All were discharged in stable condition. Table 1 summarizes the clinical characteristics of the three patients.

Variables Case 1 Case 2 Case 3
Age 47 71 61
Sex Male Female Female
Race Pilipino Hispanic Hispanic
Medical history  DM None DM, HTN
Smoking history Unknown Negative Former
Presenting complaints Cough, fever Fever, cough, SOB SOB, myalgia
Vital signs on presentation: Blood pressure mm Hg / heart rate per minute / temperature degree Celsius / respiratory rate per minute / saturation percent on room air 109-65/88/38/18/98% 196-97/105/35.8 24/83% 175-106/131 37.1/18/94
COVID-19 diagnostic test RT-PCR RT-PCR RT-PCR
Influenza diagnostic test / type Antigen detection assay/ B Antigen detection assay/ B Antigen detection assay/ A
Chest X-ray Bilateral patchy infiltrates Multi-lobar infiltrates Bilateral patchy infiltrates
Chest computed tomography Diffuse scattered areas of ground-glass and mixed attenuating opacities Diffuse bilateral ground-glass infiltrates ND
Blood culture / organism Negative Enterococcus faecium Negative
White blood cells on presentation- K/mm3 4.4 15.5 11.5
Hemoglobin- g/dl 15.1 14.4 13.7
Platelets- K/mm3 199 246 266
Creatine Kinase total- unit/L ND 58 343
Troponin- ng/ml ND 0.04 0.01
Sodium- meq/L 135 141 136
Potassium- meq/L 3.9 3.6 3.9
Chloride- meq/L 102 103 103
HCO3- meq/L 23 24 22
BUN- mg/dl 11 21 11
Creatine- mg/dl 1.23 0.65 0.75
AST/ALT-U/L 31/30 20/15 81/55
ESR- mm/hr 43 38 67
CRP- mg/L 45.8 144.5 203.2
IL-6- pg/ml 62.1 155.2 51
Fibrinogen- mg/dl ND 546 ND
Ferritin- ng/ml ND 270 76
Treatment for COVID-19 Hydroxychloroquine, azithromycin and ceftriaxone Hydroxychloroquine, azithromycin, ceftriaxone, tocilizumab convalescent plasma Hydroxychloroquine, azithromycin ceftriaxone
Treatment for influenza Oseltamivir Oseltamivir Oseltamivir
Intubation Yes Yes No
Outcome Discharged Discharged Discharged


In a metanalysis study, 3% of patients hospitalized with COVID-19 were also co-infected with another respiratory virus; respiratory syncytial virus (RSV) and influenza A being the most common viral pathogens identified [4]. Table 2 summarizes salient differences between the two viruses [4-7].

  Influenza COVID-19
Virus characteristics Influenza viruses are negative-sense single-strand RNA viruses with a segmented genome Coronaviruses are positive-sense single-stranded, RNA viruses with an unsegmented, genome
Incubation period 1 to 4 days (average 2 days) Generally, within 14 days following exposure, with most cases occurring approximately four to five days after exposure
Transmission Respiratory droplets and contact Respiratory droplets and contact
Diagnostic tests Antigen detection assays reverse-transcription polymerase chain reaction (RT-PCR), multiplex PCR, and rapid molecular assays Nucleic acid amplification testing (NAAT) most commonly with RT-PCR assay
Chest X-ray Bilateral reticular or reticulonodular opacities with or without superimposed consolidation Consolidation and ground glass opacities
Signs and symptoms Fever, headache, myalgia, malaise, cough, sore throat, and nasal discharge. Gastrointestinal illness, such as vomiting and diarrhea, is usually not part of influenza infections in adults but can occur in 10 to 20 percent of influenza infections in children. Fever, cough, dyspnea, nasal discharge, myalgias. However, diarrhea and smell or taste disorders, are also common. Other manifestations include conjunctivitis and dermatologic manifestations - maculopapular, urticarial, and vesicular eruptions and transient livedo reticularis
Laboratory abnormalities Leukocyte counts are normal or low early in the illness but may become elevated later in the illness Lymphopenia, elevated aminotransaminase levels, elevated lactate dehydrogenase levels, elevated inflammatory markers (e.g., ferritin, C-reactive protein, and erythrocyte sedimentation rate), and abnormalities in coagulation tests.
Treatment FDA-approved antiviral drugs Optimal approach to treatment of COVID-19 is uncertain. Preliminary evidence suggests role for antiviral agent - remdesivir and dexamethasone in the management of COVID-19
Vaccine FDA-licensed influenza vaccines produced annually Currently there is no vaccine to prevent COVID-19, clinical trials available
Complications Acute respiratory distress syndrome (ARDS), myositis, rhabdomyolysis, acute myocardial infarction, myocarditis and pericarditis, toxic-shock syndrome, Guillain–Barre syndrome, transverse myelitis, encephalopathy Acute respiratory distress syndrome (ARDS), myocarditis, heart failure, acute coronary syndrome, arrhythmias, cardiogenic shock, thromboembolic complications (pulmonary embolism, acute limb ischemia, mesenteric thrombosis, acute stroke), multisystem inflammatory syndrome and Guillain–Barre syndrome.
Bacterial co-infection in intensive care unit (ICU) patients More prevalent (19% of cases) Less prevalent (14% of cases)
Most commonly detected bacterial pathogen Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes Mycoplasma pneumoniae, Pseudomonas aeruginosa, Hemophilus influenzae, Klebsiella pneumoniae


In conclusion, we report three cases of co-infection of influenza and COVID-19. Health care providers should be aware of this unique situation as both can present with similar symptoms but vary in treatment. Clinicians should have a high index of suspicion in the appropriate clinical scenario. Further studies are needed to determine whether patients who have a concurrent viral infection have a worse prognosis than those in whom SARS-CoV-2 is the only detected pathogen.


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  2. Kaur P, Posimreddy S, Singh B, Qaqa F, Habib HA, Maroules M, Shamoon F: COVID-19 presenting as acute limb ischaemia. Eur J Case Rep Intern Med. 2020, 7:001724. 10.12890/2020_001724
  3. Singh B, Kaur P, Ajdir N, Gupta S, Maroules M: Covid-19 presenting as acute limb ischemia. Cureus. 2020, 22:9344. 10.7759/cureus.9344
  4. Lansbury L, Lim B, Baskaran V, Lim WS: Co-infections in people with COVID-19: a systematic review and meta-analysis. J Infect. 2020, 81:266-275. 10.1016/j.jinf.2020.05.046
  5. Krammer F, Smith GJD, Fouchier RAM, et al.: Influenza. Nat Rev Dis Primers. 2018, 4:3. 10.1038/s41572-018-0002-y
  6. Ahmad I, Rathore FA: Neurological manifestations and complications of COVID-19: a literature review. J Clin Neurosci. 2020, 77:8-12. 10.1016/j.jocn.2020.05.017
  7. Bikdeli B, Madhavan MV, Jimenez D, et al.: COVID-19 and thrombotic or thromboembolic disease: implications for prevention, antithrombotic therapy, and follow-up: JACC state-of-the-art review. J Am Coll Cardiol. 2020, 75:2950-2973. 10.1016/j.jacc.2020.04.031

Case report

COVID-19 and Influenza Co-Infection: Report of Three Cases

Author Information

Balraj Singh Corresponding Author

Hematology/Oncology, Saint Joseph's University Medical Center, Paterson, USA

Parminder Kaur

Cardiology, Saint Joseph's University Medical Center, Paterson, USA

Ro-Jay Reid

Internal Medicine, Saint Joseph's University Medical Center, Paterson, USA

Fayez Shamoon

Cardiology, Saint Joseph's University Medical Center, Patterson, USA

Mahesh Bikkina

Cardiology, Saint Joseph's University Medical Center, Paterson, USA

Ethics Statement and Conflict of Interest Disclosures

Human subjects: Consent was obtained by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

Case report

COVID-19 and Influenza Co-Infection: Report of Three Cases

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