Skip to main content

Non-febrile COVID-19 patients were common and often became critically ill: a retrospective multicenter cohort study

To the Editor:

Recent cohort studies frequently reported low rate of fever in coronavirus disease 2019 (COVID-19) patients [1, 2], which was in sharp contrast with previous studies that reported > 98% of patients presented fever on admission [3, 4]. Fever is a protective response for infections and an important criterion in the diagnosis of COVID-19. To understand the prevalence of fever in COVID-19 and its correlation with other symptoms and outcomes, we conducted a chart review of 252 hospitalized patients from 15 participating hospitals in Guangdong, Hubei, and Jiangxi provinces, China, from January 19 to March 6, 2020 (Table 1). Diagnosis of COVID-19 was based on positive severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2) reverse transcription-PCR test. Our study was approved by the institutional review boards of the Sun Yat-sen University and the participating hospitals.

Table 1 Demographics and clinical characteristics of COVID-19 patients on admission

Demographic, clinical, laboratory, treatment, and outcome data were collected. The hospital course was reviewed for severity of disease. Critically ill patients were defined as those admitted to the ICU requiring mechanical ventilation or had a fraction of inspired oxygen (FiO2) of at least 60% [5]. SPSS (Statistical Package for the Social Sciences) version 24.0 software (SPSS Inc.) was used for Mann-Whitney U, chi-square, and the Fisher’s exact test. All statistical tests were two sided, with p values of < 0.05 considered to be statistically significant.

We found that, on admission, 197 (78%) patients had temperatures ≥ 37.3 °C, 93 (37%) patients had temperatures > 38 °C, and 13 (5%) patients had temperatures > 39 °C (Table 1). We then examined the differential symptoms and outcomes between febrile (≥ 37.3 °C) and non-febrile (< 37.3 °C) patients.

The most common symptoms on admission in both febrile and non-febrile patients were cough, poor appetite, and sputum production (Table 1). Smaller proportion of the non-febrile patients presented cough, poor appetite, and sputum production, compared to the febrile patients. In contrast, larger proportion of the non-febrile patients presented cephalalgia. The negative correlation between cephalalgia and fever is intriguing. Currently, there is no evidence for SARS-CoV-2 infection in brain tissue, although ACE2 expression in neuron was observed. Perhaps inflammatory cytokines from peripheral blood caused headache [6] in COVID-19. Cephalalgia may be a useful sign for the identification of non-febrile COVID-19, when epidemiological evidence for the infection exists.

No significant difference in any of the recorded comorbidities was observed between febrile and non-febrile patients.

Similar high proportions of febrile (157 [80%]) and non-febrile patients (43 [78%]) required oxygen supplementation (Table 1), indicating that respiratory system was the most affected system for both groups of patients. Among these, 17 (9%) febrile and 4 (7%) non-febrile patients developed acute respiratory distress syndrome (ARDS). Forty-three (17%) febrile and 9 (16%) non-febrile patients were admitted to the ICU. Critical illness was similarly common in the febrile (40 patients [20%]) and non-febrile (12 patients [22%]) patients.

Fever promotes inflammatory reaction, which may help control viral infection leading to beneficial outcomes. However, fever-induced upregulation of the inflammatory cytokines such as IL-1, TNF, and IL-6 may contribute to cytokine storm that contributes to critical illness. These double-edged effects of fever may explain the absence of correlation between fever and the disease outcome.

Given the high proportion of non-febrile patients in COVID-19, and that 20% non-febrile patients became critically ill, heightened attention for this elusive group of patients may be required for a better containment of the pandemic. Our finding is a timely alarm for health care workers and general population that temperature monitoring alone does not identify many of the COVID-19 patients.

Availability of data and materials

The data that support the findings of this study are available from the corresponding author upon reasonable request.



Acute respiratory distress syndrome


Coronavirus disease 2019

FiO2 :

Fraction of inspired oxygen


Severe acute respiratory syndrome-related coronavirus-2


  1. 1.

    Goyal P, Choi JJ, Pinheiro LC, Schenck EJ, Chen R, Jabri A, Satlin MJ, Campion TR Jr, Nahid M, Ringel JB, et al. Clinical characteristics of COVID-19 in New York City. N Engl J Med. 2020.

  2. 2.

    Richardson S, Hirsch JS, Narasimhan M, Crawford JM, McGinn T, Davidson KW, the Northwell C-RC, Barnaby DP, Becker LB, Chelico JD, et al. Presenting characteristics, comorbidities, and outcomes among 5700 patients hospitalized with COVID-19 in the New York City area. JAMA. 2020;323(20):2052-9.

  3. 3.

    Wang D, Hu B, Hu C, Zhu F, Liu X, Zhang J, Wang B, Xiang H, Cheng Z, Xiong Y, et al. Clinical characteristics of 138 hospitalized patients with 2019 novel coronavirus-infected pneumonia in Wuhan, China. JAMA. 2020;323(11):1061-9.

  4. 4.

    Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, Zhang L, Fan G, Xu J, Gu X, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet. 2020;395(10223):497-506.

  5. 5.

    Yang X, Yu Y, Xu J, Shu H, Xia J, Liu H, Wu Y, Zhang L, Yu Z, Fang M, et al. Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study. Lancet Respir Med. 2020;8(5):475-81.

  6. 6.

    Zhang X, Burstein R, Levy D. Local action of the proinflammatory cytokines IL-1beta and IL-6 on intracranial meningeal nociceptors. Cephalalgia. 2012;32(1):66-72.

Download references


We thank Drs. Jie Li, Guangjun Yan (Jingzhou Hospital of Traditional Chinese Medicine, China), Yunle Wan, Yifeng Zou (The Six Affiliated Hospital of Sun Yat-sen University, China), Lihan Shen (Dongguan People’s Hospital, China), and Shudong Jiang (Jieyang People’s Hospital, China) for assistance in the data collection.


This study was partially supported by the National Natural Science Foundation of China 81770571 (to LZ), 81970452 (to PL), 81774152 (to RZ); the Guangzhou Science and Technology Plan Projects 201803040019 (to PL); Guangdong Province “Pearl River Talent Plan” Innovation and Entrepreneurship Team Project (2019ZT08Y464); Sun Yat-sen University 5010 project 2010012 (to PL); and the National Key Clinical Discipline of China.

Author information




LZ, RL, and PL conceived and designed this study. YL, NJ, SC, and LZ collected the data. All authors analyzed the data. YL, NJ, and LZ prepared the manuscript. All authors critically revised the manuscript and approved the final version.

Corresponding authors

Correspondence to Lixin Zhu or Ruixin Zhu or Ping Lan.

Ethics declarations

Ethics approval and consent to participate

Our study was approved by the institutional review boards of the Sun Yat-sen University and the participating hospitals. The informed consent was waived because this chart review did not involve any patient tissue or interview.

Consent for publication

Not applicable.

Competing interests

All authors declare no competing interests.

Additional information

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Li, Y., Jiao, N., Zhu, L. et al. Non-febrile COVID-19 patients were common and often became critically ill: a retrospective multicenter cohort study. Crit Care 24, 314 (2020).

Download citation


  • COVID-19
  • SARS-CoV-2
  • Fever
  • Febrile
  • Critical