Asymptomatic infections — Asymptomatic infections have also been described [
34,48-50], but their frequency is unknown.
In a COVID-19 outbreak on a cruise ship where nearly all passengers and staff were screened for SARS-CoV-2, approximately 17 percent of the population on board tested positive as of February 20; about half of the 619 confirmed COVID-19 cases were asymptomatic at the time of diagnosis [
51].
Even patients with asymptomatic infection may have objective clinical abnormalities. In another study of 24 patients with asymptomatic infection who all underwent chest computed tomography (CT), 50 percent had typical ground-glass opacities or patchy shadowing, and another 20 percent had atypical imaging abnormalities [
21]. Five patients developed low-grade fever, with or without other typical symptoms, a few days after diagnosis.
Clinical manifestations
Initial presentation — Pneumonia appears to be the most frequent serious manifestation of infection, characterized primarily by fever, cough, dyspnea, and bilateral infiltrates on chest imaging [
33,37-39]. There are no specific clinical features that can yet reliably distinguish COVID-19 from other viral respiratory infections.
In a study describing 138 patients with COVID-19 pneumonia in Wuhan, the most common clinical features at the onset of illness were [
39]:
●Fever in 99 percent
●Fatigue in 70 percent
●Dry cough in 59 percent
●Anorexia in 40 percent
●Myalgias in 35 percent
●Dyspnea in 31 percent
●Sputum production in 27 percent
Other cohort studies of patients from Wuhan with confirmed COVID-19 have reported a similar range of clinical findings [
37,39,52,53]. However, fever might not be a universal finding. In one study, fever was reported in almost all patients, but approximately 20 percent had a very low grade fever <100.4°F/38°C [
37]. In another study of 1099 patients from Wuhan and other areas in China, fever (defined as an axillary temperature over 99.5°F/37.5°C) was present in only 44 percent on admission but was ultimately noted in 89 percent during the hospitalization [
33].
Other, less common symptoms have included headache, sore throat, and rhinorrhea. In addition to respiratory symptoms, gastrointestinal symptoms (eg, nausea and diarrhea) have also been reported in some patients, but these are relatively uncommon [
37,39].
Reports of cohorts in locations outside of Wuhan have described similar clinical findings, although some have suggested that milder illness may be more common [
54-56]. As an example, in a study of 62 patients with COVID-19 in the Zhejiang province of China, all but one had pneumonia, but only two developed dyspnea, and only one warranted mechanical ventilation [
55].
Course and complications — As above, symptomatic infection can range from mild to critical. (See
'Spectrum of illness severity' above.)
Some patients with initially mild symptoms may progress over the course of a week. In one study of 138 patients hospitalized in Wuhan for pneumonia due to SARS-CoV-2, dyspnea developed after a median of five days since the onset of symptoms, and hospital admission occurred after a median of seven days of symptoms [
39]. In another study, the median time to dyspnea was eight days [
37].
Acute respiratory distress syndrome (ARDS) is a major complication in patients with severe disease. In the study of 138 patients described above, ARDS developed in 20 percent after a median of eight days, and mechanical ventilation was implemented in 12.3 percent [
39]. In another study of 201 hospitalized patients with COVID-19 in Wuhan, 41 percent developed ARDS; age greater than 65 years, diabetes mellitus, and hypertension were each associated with ARDS [
57].
Other complications have included arrhythmias, acute cardiac injury, and shock. In one study, these were reported in 17, 7, and 9 percent, respectively [
39].
According to the WHO, recovery time appears to be around two weeks for mild infections and three to six weeks for severe disease [
4].
Laboratory findings — In patients with COVID-19, the white blood cell count can vary. Leukopenia, leukocytosis, and lymphopenia have been reported, although lymphopenia appears most common [
23,37-39]. Elevated lactate dehydrogenase and ferritin levels are common, and elevated aminotransferase levels have also been described. On admission, many patients with pneumonia have normal serum procalcitonin levels; however, in those requiring intensive care unit (ICU) care, they are more likely to be elevated [
37-39].
High D-dimer levels and more severe lymphopenia have been associated with mortality [
38].
Imaging findings — Chest CT in patients with COVID-19 most commonly demonstrates ground-glass opacification with or without consolidative abnormalities, consistent with viral pneumonia [
53,58]. Case series have suggested that chest CT abnormalities are more likely to be bilateral, have a peripheral distribution, and involve the lower lobes. Less common findings include pleural thickening, pleural effusion, and lymphadenopathy.
Chest CT may be helpful in making the diagnosis, but no finding can completely rule in or rule out the possibility of COVID-19. In a study of 1014 patients in Wuhan who underwent both reverse-transcription polymerase chain reaction (RT-PCR) testing and chest CT for evaluation of COVID-19, a "positive" chest CT for COVID-19 (as determined by a consensus of two radiologists) had a sensitivity of 97 percent, using the PCR tests as a reference; however, specificity was only 25 percent [
59]. The low specificity may be related to other etiologies causing similar CT findings. In another study comparing chest CTs from 219 patients with COVID-19 in China and 205 patients with other causes of viral pneumonia in the United States, COVID-19 cases were more likely to have a peripheral distribution (80 versus 57 percent), ground-glass opacities (91 versus 68 percent), fine reticular opacities (56 versus 22 percent), vascular thickening (59 versus 22 percent), and reverse halo sign (11 versus 1 percent), but less likely to have a central and peripheral distribution (14 versus 35 percent), air bronchogram (14 versus 23 percent), pleural thickening (15 versus 33 percent), pleural effusion (4 versus 39 percent), and lymphadenopathy (2.7 versus 10 percent) [
60]. A group of radiologists in that study was able to distinguish COVID-19 with high specificity but moderate sensitivity.
In one report of 21 patients with laboratory-confirmed COVID-19 who did not develop severe respiratory distress, lung abnormalities on chest imaging were most severe approximately 10 days after symptom onset [
52]. However, chest CT abnormalities have also been identified in patients prior to the development of symptoms and even prior to the detection of viral RNA from upper respiratory specimens [
53,61].