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Original article

Vol. 151 No. 4950 (2021)

Mimics and chameleons of COVID-19: patient presentation and accuracy of triage during the first wave

  • Andrea S. Jauslin
  • Noemi R. Simon
  • Nina L. Giudici
  • Marco Rueegg
  • Tobias Zimmermann
  • Matthias Diebold
  • Sarah Tschudin-Sutter
  • Raphael Twerenbold
  • Christian H. Nickel
  • Roland Bingisser
Cite this as:
Swiss Med Wkly. 2021;151:w30103


STUDY AIMS: To quantify mimics and chameleons of coronavirus disease 2019 (COVID-19), to analyse the diagnostic accuracy of the triage protocol, and to describe the resulting groups of mimics and chameleons – including their presenting symptoms and final diagnoses.

METHODS: Diagnostic accuracy study including all adult patients tested for severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) at the emergency department of the University Hospital Basel, Switzerland during the first wave of pandemic in spring 2020. Diagnostic accuracy of triage was determined by calculating sensitivity, specificity, positive and negative predictive value, and positive and negative likelihood ratio. Triage to the group of suspected (+) and not suspected (–) COVID-19 was considered the index test, whereas a SARS-CoV-2 polymerase chain reaction test result was used as reference standard. Mimics were defined as false positives and chameleons as false negatives.

RESULTS: Of 2898 patients included in the analysis, 191 were true positives, 895 were false positives (mimics), 9 were false negatives (chameleons) and 1803 were true negatives. This resulted in a sensitivity of 0.95 (95% confidence interval [CI] 0.92–0.98) and a specificity of 0.67 (95% CI 0.65–0.69) for standardised triage. Among mimics, the main categories of final diagnoses were other infections (n = 513, 57.3%), cardiovascular diseases (excluding cerebrovascular) (n = 125, 14%), and non-infectious diseases of the respiratory system (n = 84, 9.4%). Fever (n = 357, 39.9% vs n = 104, 54.5%), cough (n = 466, 52.1% vs n = 126 66%), and smell or taste dysfunction (n = 60, 6.7% vs n = 24, 12.6%) were less frequently observed in mimics than in COVID-19 patients. Eight of nine COVID-19 chameleons presented with either nonspecific complaints (weakness and/or fatigue) or gastrointestinal symptoms.

CONCLUSION: The quantitative assessment of COVID-19 mimics and chameleons showed a high prevalence of mimics. Clinical differentiation between true positives and false positives is not feasible due to largely overlapping symptoms. Prevalence of chameleons was very low.


  1. Lai CC, Ko WC, Lee PI, Jean SS, Hsueh PR. Extra-respiratory manifestations of COVID-19. Int J Antimicrob Agents. 2020 Aug;56(2):106024.
  2. Marzano AV, Cassano N, Genovese G, Moltrasio C, Vena GA. Cutaneous manifestations in patients with COVID-19: a preliminary review of an emerging issue. Br J Dermatol. 2020 Sep;183(3):431–42.
  3. Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet. 2020 Feb;395(10223):497–506.
  4. Coleman JJ, Manavi K, Marson EJ, Botkai AH, Sapey E. COVID-19: to be or not to be; that is the diagnostic question. Postgrad Med J. 2020 Jul;96(1137):392–8.
  5. Madjid M, Safavi-Naeini P, Solomon SD, Vardeny O. Potential Effects of Coronaviruses on the Cardiovascular System: A Review. JAMA Cardiol. 2020 Jul;5(7):831–40.
  6. Ellul MA, Benjamin L, Singh B, Lant S, Michael BD, Easton A, et al. Neurological associations of COVID-19. Lancet Neurol. 2020 Sep;19(9):767–83.
  7. Rogers JP, Chesney E, Oliver D, Pollak TA, McGuire P, Fusar-Poli P, et al. Psychiatric and neuropsychiatric presentations associated with severe coronavirus infections: a systematic review and meta-analysis with comparison to the COVID-19 pandemic. Lancet Psychiatry. 2020 Jul;7(7):611–27.
  8. Clifford CT, Pour TR, Freeman R, Reich DL, Glicksberg BS, Levin MA, et al. Association between COVID-19 diagnosis and presenting chief complaint from New York City triage data. Am J Emerg Med. 2021 Aug;46:520–4.
  9. WHO. COVID-19 Case definition. Updated 16.12.2020. Accessed 21 June 2021.
  10. Mansella G, Rueegg M, Widmer AF, Tschudin-Sutter S, Battegay M, Hoff J, et al. COVID-19 Triage and Test Center: Safety, Feasibility, and Outcomes of Low-Threshold Testing. J Clin Med. 2020 Oct;9(10):3217.
  11. Nickel CH, Bingisser R. Mimics and chameleons of COVID-19. Swiss Med Wkly. 2020 Mar;150(13-14):w20231.
  12. Worster A, Bledsoe RD, Cleve P, Fernandes CM, Upadhye S, Eva K. Reassessing the methods of medical record review studies in emergency medicine research. Ann Emerg Med. 2005 Apr;45(4):448–51.
  13. Gilbert EH, Lowenstein SR, Koziol-McLain J, Barta DC, Steiner J. Chart reviews in emergency medicine research: where are the methods? Ann Emerg Med. 1996 Mar;27(3):305–8.
  14. Cohen JF, Korevaar DA, Altman DG, Bruns DE, Gatsonis CA, Hooft L, et al. STARD 2015 guidelines for reporting diagnostic accuracy studies: explanation and elaboration. BMJ Open. 2016 Nov;6(11):e012799.
  15. Meng X, Deng Y, Dai Z, Meng Z. COVID-19 and anosmia: A review based on up-to-date knowledge. Am J Otolaryngol. 2020 Sep - Oct;41(5):102581.
  16. Cherry G, Rocke J, Chu M, Liu J, Lechner M, Lund VJ, et al. Loss of smell and taste: a new marker of COVID-19? Tracking reduced sense of smell during the coronavirus pandemic using search trends. Expert Rev Anti Infect Ther. 2020 Nov;18(11):1165–70.
  17. Oxley TJ, Mocco J, Majidi S, Kellner CP, Shoirah H, Singh IP, et al. Large-Vessel Stroke as a Presenting Feature of Covid-19 in the Young. N Engl J Med. 2020 May;382(20):e60.
  18. Avula A, Nalleballe K, Narula N, Sapozhnikov S, Dandu V, Toom S, et al. COVID-19 presenting as stroke. Brain Behav Immun. 2020 Jul;87:115–9.
  19. Beyrouti R, Adams ME, Benjamin L, Cohen H, Farmer SF, Goh YY, et al. Characteristics of ischaemic stroke associated with COVID-19. J Neurol Neurosurg Psychiatry. 2020 Aug;91(8):889–91.
  20. Spence JD, de Freitas GR, Pettigrew LC, Ay H, Liebeskind DS, Kase CS, et al. Mechanisms of Stroke in COVID-19. Cerebrovasc Dis. 2020;49(4):451–8.
  21. Schittek GA, Bornemann-Cimenti H, Sandner-Kiesling A. Wellbeing of ICU patients with COVID-19. Intensive Crit Care Nurs. 2021 Aug;65:103050.
  22. Roubille C, Ribstein J, Hurpin G, Fesler P, Fiat E, Roubille F. Confidence vanished or impaired until distrust in the doctor-patient relationship because of COVID-19: Confidence vanished or impaired until distrust: “COVID” in relationship. Rev Med Interne. 2021 Jan;42(1):58–60.
  23. Crowe S, Howard AF, Vanderspank-Wright B, Gillis P, McLeod F, Penner C, et al. The effect of COVID-19 pandemic on the mental health of Canadian critical care nurses providing patient care during the early phase pandemic: A mixed method study. Intensive Crit Care Nurs. 2021 Apr;63:102999.
  24. Weilenmann S, Ernst J, Petry H, Pfaltz MC, Sazpinar O, Gehrke S, et al. Health Care Workers’ Mental Health During the First Weeks of the SARS-CoV-2 Pandemic in Switzerland-A Cross-Sectional Study. Front Psychiatry. 2021 Mar;12:594340.
  25. González-Gil MT, González-Blázquez C, Parro-Moreno AI, Pedraz-Marcos A, Palmar-Santos A, Otero-García L, et al. Nurses’ perceptions and demands regarding COVID-19 care delivery in critical care units and hospital emergency services. Intensive Crit Care Nurs. 2021 Feb;62:102966.
  26. Leuzinger K, Roloff T, Gosert R, Sogaard K, Naegele K, Rentsch K, et al. Epidemiology of Severe Acute Respiratory Syndrome Coronavirus 2 Emergence Amidst Community-Acquired Respiratory Viruses. J Infect Dis. 2020 Sep;222(8):1270–9.
  27. Liang M, Gao L, Cheng C, Zhou Q, Uy JP, Heiner K, et al. Efficacy of face mask in preventing respiratory virus transmission: A systematic review and meta-analysis. Travel Med Infect Dis. 2020 Jul - Aug;36:101751.
  28. Chu DK, Akl EA, Duda S, Solo K, Yaacoub S, Schünemann HJ, et al.; COVID-19 Systematic Urgent Review Group Effort (SURGE) study authors. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. Lancet. 2020 Jun;395(10242):1973–87.
  29. Carpenter CR, Mudd PA, West CP, Wilber E, Wilber ST. Diagnosing COVID-19 in the Emergency Department: A Scoping Review of Clinical Examinations, Laboratory Tests, Imaging Accuracy, and Biases. Acad Emerg Med. 2020 Aug;27(8):653–70.
  30. England PH. Investigation and initial clinical management of possible cases of Wuhan novel coronavirus (WN-CoV) infection Updated 14 December2020. Accessed 21 June 2021.

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