Table 1.
Characteristics of included studies in systematic review.
| Author | Year | Type of study | Country | Total of asymptomatic individuals | Male (n, %) | Age (mean, SD) | Type of risk contact | Length of asymptomatic period | Clinical and imaging features | Treatment | Outcomes of patients at the end of study |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Hu et al. | 2020 | Cross-sectional | China | 24 | 8 (33.3) | 32.5 (IQR 5–95) | All were close contacts of COVID-19 patients in Nanjing | 5 patients (20.8%) developed symptoms during follow-up. Median length of asymptomatic period: 1 day (2 patients with 0 day, 2 patients with 1 day, and 1 patient with 2 days) | Clinical: All the five cases developed fever without chills, with body temperatures ranges 36.5 °C–38.0 °C, but none presented high fever (>39 °C). One case also had cough, fatigue and nasal congestion. Another case presented cough, fatigue, dizziness and arthralgia. Images: Twelve (50.0%) cases showed ground-glass or patchy shadows in lungs in their chest CT images. Five (20.8%) cases showed stripe shadows in lungs, an atypical image finding. | 21 cases (87.5%) received antiviral therapy. One case also received antibiotics therapy, antifungal therapy plus immunoglobin therapy. Immunoglobin therapy was also given to 2 cases. All these cases were treated with interferon atomization. None of the cases developed severe pneumonia, requiring systemic corticosteroids treatment, mechanical ventilation, or admission to ICU. | 18 cases (75.0%) had the virus cleared (2 continuous negatives of nucleic acid tests), among whom 9 cases were discharged from the hospital while the rest 9 were kept in hospital for further observation. Six cases had nucleic acid tests reversed to positive after one negative result. Of particular concern, one case showed positive again even after the continuous negative of nucleic acid tests. |
| Tuo Ji et al. | 2020 | Cross-sectional | China | 41 | Not reported | Not reported | They had epidemiological clues for COVID-19 contact | Not mentioned | Not mentioned | Not mentioned | After quarantined for at least 14 days, all the persons had no signs of illness |
| Kimball et al. | 2020 | Cross-sectional | USA | 13 | Not reported | Not reported | They had history of exposure to epidemic areas or close contact with an infected individual. | 3 cases stay asymptomatic during the follow-up 1 week. The rest 10 cases developed symptoms and the mean interval from testing to symptom onset in the presymptomatic residents was 3 days | Clinical: fever (eight residents), malaise (six), and cough (five). | Not mentioned | Not mentioned |
| Wang Xiaobing et al. | 2020 | Cross-sectional | China | 30 | Not reported | Not reported | They had history of exposure to epidemic areas or close contact with an infected individual. | 14 cases stay asymptomatic during the follow-up 24 days | Clinical: 16 cases developed symptoms, Fever occurred in 6 of 30 ones (20%), with cough in 8 of 30 (26.7%), myalgia in 3 of 30 (10%), dyspnea in 2 of 30(6.7%), runny nose in 1 of 30(3.3%), nasal congestion in 1 of 30 (3.3%) and abdominal pain in 3.3%. Images: Not mentioned | Not mentioned | 2(2.0%) patients with aggravation of illness during follow up(n = 100) |
| Wang Y.et al. | 2020 | Cross-sectional | China | 55 | 22 (40%) | 49 (IQR 2–69) | Close contact with family member diagnosticated with SARS-CoV-2 infection | 70.9% developed symptoms during follow-up. 1–7 days | Clinical: Seven cases had mild cough and seven cases had low fever 3–5 days later (two cases presenting both cough and fever, which later complicated with hypoxia (SpO2 = 90%) and restlessness). Images: 16 (29.1%; 16/55) patients showed normal first chest CT. 37 cases showed pneumonia in first chest CT | Lopinavir/Ritonavir was given to all cases as initial therapy for 7 days. Two cases with hypoxia received intravenous immunoglobulin 10 g/day and methylprednisolone (1–2 mg/kg/day) therapy for 3 days. Heated humidified high-flow nasal cannula (HHHFNC) was used for 5 days. Eventually, the two patients recovered without complication | None of the cases were admitted to ICU. All the cases recovered and were discharged home |
| Meng et al. | 2020 | Cross-sectional | China | 58 | 26(44.8%) | 42.6 (16.6) | Epidemiological history (100%) | 3.71 ± 2.86 days | Clinical: eight patients developed fever; nine patients developed cough; eight patients developed fatigue; two patients developed shortness of breath; and one patient developed diarrhea. Images: frequent findings in CT were multiple lesions (62.1%), bilateral lesions (41.4%), peripheral distribution (75.9%) and ground glass opacities (51.7%) | Not mentioned | All patients were discharged after treatment. |
| Breslin et al. | 2020 | Cross-sectional | USA | 14 | 0 (0) | Not reported | Not mentioned | 6 patients developed symptoms within the first seven days after positive swab result. 4 stays asymptomatic. | Clinical: 8 patients developed fever intra or post-partum. 6 patients developed cough, myalgias, chest pain, anosmia, and/or dysgeusia. 2 patients were admitted to ICU due to obstetrical complications including respiratory distress. Images: Not mentioned | Patients with intra or postpartum fever received antibiotics for suspected intraamniotic infection or endometritis | 13 patients (including 1 ICU-admitted patient) were discharged. The other remaining patient stays in ICU with renal Insufficiency without mechanical ventilation nor dialysis |
| Kong et al. | 2020 | Cross-sectional | China | 100 | 55 (55.0%) | 37.7 ± 19.0 | History of recent travel or residence in the outbreak area or Contact history with COVID-19 patients. | 17 (27.4%) developed relevant symptoms days (median: 7 days, range: 1–13 days) after diagnosis |
Cough, Pharyngalgia or Runny nose, Fever, Chills or fatigue, Muscle aches or headaches. Among the 60 asymptomatic cases who demonstrated positive CT findings, 37 cases showed typical multiple peripheral patchy ground glass opacities, some of who showed parenchymal consolidation, interlobular septal thickening, bronchial wall thickening and halo signs or reverse-halo signs. Eighteen cases showed single or several scattered ground glass opacities. 5 cases showed nodular ground glass opacities. |
antiviral therapy if the CT imaging showed positive findings for pneumonia. | There were no deaths in the asymptomatic group. All other patients were discharged from the hospital |
| Lu Y et al. | 2020 | Cross-sectional | China | 29 | 17 (58.6%) | 7 (interquartile range 6–11) | Not mentioned | Stay asymptomatic | Non symptoms. 9 (32%) has pneumonia in chest radiological study | All patients were administered antiviral therapy, of which interferon-α nebulization was the most frequently used. None of the patients required oxygen therapy. |
All patients discharge after 10 days |
| Ma et al. | 2020 | Retrospective cohort study | China | 11 | 6(54.5) | 23(range 1–60) | 3 were residents of Wuhan,1 Wuhan visitor, 7 close contact with confirmed case | Stay asymptomatic | 7 have patchy shadows or ground glass opacity on CT | All patients received antiviral treatment, including lopinavir/ritonavir tablets, arbidol, and inhalation of recombinant human interferon |
9(81.8) of them discharge at the end of the follow-up, and 2 remain hospitalized because they still positive |
| Wang Y et al. | 2020 | Retrospective cohort study | China | 63 | 34(54%) | 39.30 ± 16.45 | 17(27%) Exposure history in Hubei and 18(28.6%) family cluster | Stay asymptomatic | Non symptoms.29 had anormal chest CT findings | Antiviral treatment with α-Interferon inhalation and Lopinavir/Ritonavir oral with Thymosin injection | All patients were discharged |
| Xu et al. | 2020 | Retrospective cohort study | China | 15 | 10 (66.7) | 27.0 (17.0, 36.0) | Contact with suspected or confirmed patients | Stay asymptomatic | Non symptoms. Ground‐glass opacity (40%) and pneumonia(52%) | interferon α‐2b, arbidol, lopinavir/ritonavir | All patients were discharged |
| London et al. | 2020 | Retrospective cohort study | USA | 22 | 0(0%) | 30.5 (interquartile range 24.5–34.8) | Testing for COVID-19 became universal for all antepartum and labor and delivery admissions | Stay asymptomatic | Non symptoms. Images nor mentioned | No treatment | All discharge after 10 days |
| Qiu et al. | 2020 | Retrospective cohort study | China | 10 | Not reported | Not reported | They had history of exposure to epidemic areas or close contact with an infected individual. | Stay asymptomatic | Non symptoms. Images: No abnormal radiographic | Interferon alfa treatment | In one case: 10 days to become SARS-CoV-2 PCR-negative. All patients were cured. |
| Albano et al. | 2020 | Case series | Italy | 6 | 2 (33.3) | 62.2 (8.7) | Not mentioned | 2 patients developed symptoms | Clinical: Case 4: several days later of the diagnosis, fever and dyspnoea appeared Case 7: Fever and cough appeared one day after the scan. Images: No reported | Hydroxychloroquine plus Ritonavir/Lopinavir (3 cases) | Not mentioned |
| Dong et al. | 2020 | Case series | China | 1 | 1(100%) | 26 | Nurse, contact with an infected person | Stay asymptomatic | Non symptoms. Chest CT with no sign of pneumonia | Treated with antiviral drugs including Arbidol and Prezcobix (Darunavir and Cobicistat tablets) | Discharged 4 days later after testing negative in two consecutive RT-PCR assays |
| Lin et al. | 2020 | Case report | China | 1 | 1(100%) | 61 | Close contact with a novel coronavirus pneumonia patient more than 10 days prior admission | Since admission, the patient has remained with only mild shortness of breath after activity on the 11th day of admission | Clinical: Mild shortness of breath after activity on the 11th day of admission. Images: Day 1: CT showed multiple ground glass opacities in the right lung. Day 3, CT revealed an enlarged lesion with small areas of consolidation in the center. Day 6, CT showed a further increase of lesions. Day 9, CT showed the lesions progressed further and involved both lungs, with thickened interlobular septa around the lesion in the upper lobe of the right lung; in addition, there were small bilateral pleural effusions. Day 23, CT showed that pleural effusions had resolved, and bilateral pulmonary lesions improved | During hospitalization the main treatment has been oral antiviral drugs (Lopinavir and Ritonavir tablets), interferon and methylprednisolone | Day 23: Patient remains hospitalized because his nucleic acid test is still positive |
| Ling et al. | 2020 | Case report | China | 4 | Not reported | Not reported | The majority patients had a history of exposure in Wuhan or to infected patients | Stay assymptomatic | Non symptoms. Images: Chest CT images showed no significant abnormalities | Not mentioned | 2 of 4 patients subsequently presented two consecutives negative nucleic acid detection at least 24 h apart and finally recovered |
| Nicastri et al. | 2020 | Case report | Italy | 1 | 1(100%) | Not reported | Contact with Wuhan person | The patients developed signs during follow-up | Clinical: Day 2: Mild conjunctivitis. Day 10–11: Tonsillar exudate. Images: Chest CT were normal | Lopinavir/ritonavir | The isolation regimen was stopped, and the patient discharged at the end of 14-day quarantine after obtaining two SARS-CoV-2 negative samples 24 h apart near |
| Polverari et al. | 2020 | Case report | Italy | 1 | 1(100%) | 73 | Patient declared no suspected expositions to infected people | 3 days | Images: PET/CT revealed the presence of bilateral, diffuse and peripheral predominant ground-glass opacities in the lower lobes | Not mentioned | Patient with non-small cells lung cancer, 3 days after the diagnosis intensive care unit was necessary for rapid disease progression and severe respiratory distress syndrome. |
| Poli et al. | 2020 | Case report | Italy | 1 | 1(100%) | 1 month | Close contact with the grandfather who was later hospitalized for COVID-19 | Stay asymptomatic | Non symptoms. Images not reported | Not mentioned | Not mentioned |
| Bai et al. | 2020 | A case report of familial cluster | China | 1 | 0 | 20 | lives in Wuhan | Stay asymptomatic | Non symptoms. Images: Chest CT images showed no significant abnormalities | Not mentioned | Not mentioned |
| Chan et al. | 2020 | A case report of familial cluster | China | 1 | 1(100%) | 10 | close contacts of COVID-19 patient | Stay asymptomatic | Non symptoms. Images: ground-glass lung opacities | Not mentioned | Admitted to hospital under isolation, supportive care, and remained stable at 9th day |
| Le et al. | 2020 | A case report of familial cluster | China | 1 | 1(100%) | 55 | Contact with Wuhan person | Stay asymptomatic | Non symptoms. Images not mentioned | Not mentioned | Patient was discharged after 2 consecutive negative PCR results |
| Lu S. et al. | 2020 | A case report of familial cluster | China | 2 | 0 | Not reported | Relatives (elder sister and son) of a coronavirus confirmed patients | Both patients stay asymptomatic | Non symptoms. Images: Patient B: Chest CT showed multiple patchy and ground glass shadows in both lungs. Patient C: No signs in chest CT | Both patients were given ribavirin plus interferon antiviral and symptomatic treatment | Not mentioned |
| Pan et al. | 2020 | A case report of familial cluster | China | 2 | 1(50%) | Not reported | Contact with Wuhan person | Stay asymptomatic | Non symptoms. Images: Normal CT chest | Not mentioned | Not mentioned |
| Qian et al. | 2020 | A case report of familial cluster | China | 2 | 1(100%) | Not reported | Husband and one grandchildren of an index case | Both patients stay asymptomatic | Non symptoms. Images nor mentioned | Not mentioned | Not mentioned |
| Tong et al. | 2020 | A case report of familial cluster | China | 3 | 1(33.3%) | 28(IQR 12–42) | Wife of an index case. Son and wife of another index case | Patients stay asymptomatic | Non symptoms. Images nor mentioned | Not mentioned | Not mentioned |
| Ye et al. | 2020 | A case report of familial cluster | China | 3 | 3(100%) | 28(IQR 23–50) | Contact with Wuhan person | One case stay asymptomatic, the rest developed symptoms 1 and 2 days later. during follow-up 4 weeks | Clinical: 2 patients developed fever and cough. Images: Chest CT images showed Ground-glass changes (Case 3 and 5). No abnormalities of Case 2 | Not mentioned | In case 2: 10 days to become PCR-negative. The rest still hospitalized and PCR-positive |
| Zhang et al. | 2020 | A case report of familial cluster | China | 1 | 1(100%) | 10 | Contact with an infected person | Stay asymptomatic | Non symptoms. Images: chest radiograph demonstrated ground glass opacities | Not mentioned | 22 days later the patient was discharged. |
| Sutton et al. | 2020 | Case series | USA | 29 | 0 (0) | Not reported | Lives in New York | 26 patients stay asymptomatic and three patients developed fever before postpartum discharge (median length of stay, 2 days) | Clinical: Fever developed in 3 patients before postpartum discharge | Two febrile patients received antibiotics for presumed endomyometritis (although 1 patient did not have localizing symptoms), and one patient received supportive care | Not mentioned |
| Du et al. | 2020 | Case series | China | 8 | 5 (62.5%) | Not reported | Familial cluster | 5.43 ± 6.33 days. | Clinical: three patients developed mild symptoms, and five patients developed conventional symptoms. Images: frequent findings were lung injury (five patients) and bilateral lesions (three patients). | Treated according to the plan of the National Health Commission (trial version 5) | Not mentioned |
| Samsami et al. | 2020 | Case series | Iran | 8 | 5 (62%) | 49.7(13.1) | 5 patients had history of close contact with a suspected COVID-19 case | Two patients experienced mild symptoms during hospitalization. Six patients remained asymptomatic | Clinical: Two patients developed fever, cough, and myalgia. Images: Chest CT showed findings compatible with pneumonia in all patients | All patients received hydroxychloroquine with or without azithromycin | All patients were discharged from hospital. None of the patients required ICU |
| Zhou et al. | 2020 | Case series | China | 13 | Not reported | Not reported | Close contact of confirmed cases | 10 patients remained asymptomatic and three patients developed symptoms at the second day of hospitalization | Images: 12 patients showed multiple ground-glass opacities and four of these showed radiographic progression during hospitalization, but all showed improvement before discharge. One patient had no evidence of radiographic abnormalities consistent with COVID-19. Clinical: Three patients developed symptoms at the second day of hospitalization (sore throat, non-productive cough, chest distress, and diarrhea). |
Not mentioned | All patients tested SARS-CoV-2-RT-PCR-negative at a median time of 13 days (range 3–19 days). |
| See et al. | 2020 | Case series | Malaysia | 4 | 3 (75%) | 6.4 (4.3) | Contact with an infected person in china | Only one patient remained asymptomatic | Clinical: case 1 had fever and diarrhea, case 2 has fever and upper respiratory tract symptoms, and case 3 had mild cough and wheeze. Images: chest X-ray showed opacities in two patients. No information on the rest. | Paracetamol in two patients, penicillin V in one patient | All patients recovered |
| An et al. | 2020 | Case series | China | 25 | Not reported | Not reported | 22 were family members in care of confirmed patients with COVID-19. 3 patients were cleaning of medical waste and hospital-transportation staff | 16 stars asymptomatic. Nine patients developed symptoms. | Clinical: 9 patients developed mild cough and/or other symptoms. Images: 24 patients had abnormal CT findings in the lung. Approximately two-thirds had an involvement of a single lobe, and two-thirds had only a ground-glass density shadow. | The 9 symptomatic patients received chloroquine 500 mg twice daily for seven days and Arbidol 200 mg three times a day for no more than ten days. | All patients recovered. 16 recovered without any symptoms during the follow-up, and 9 recovered with resolved symptoms. |
| Danis et al. | 2020 | Case series | France | 1 | Not reported | Not reported | Contact with an infected person | Stay asymptomatic | Non symptoms. Images nor mentioned | No anti-viral treatment | The symptoms of all cases resolved rapidly, without anti-viral treatment |
| Chang M. et al. | 2020 | Case series | Republic of Korea | 10 | 6(60%) | 65 ± 12.8 years | Contact history with COVID-19 patients | Stay asymptomatic | Non symptoms. All patients (100%) had ground glass opacity (GGO) on chest CT predominantly distributed peripherally and posteriorly | hydroxychloroquine sulfate and lopinavir/ritonavir | All patients were discharged from hospital. None of the patients required ICU |
| Kim et al. | 2020 | Case series | Korea of South | 10 | 4(40%) | 31 years (interquartile range 17.8–55.8 years). | Contact with confirmed COVID-19 case |
7 patients stay asymptomatic and 3 patients developed symptoms 1 or 2 days later the diagnosis | Three patients who were asymptomatic on admission developed myalgia, fever, and a cough. | No anti-viral treatment | It was found that RT-PCR was indeterminate or negative 14 days after diagnosis in entirely asymptomatic individuals |
| Song et al. | 2020 | Case series | China | 8 | 5(62.5%) | 10.1 ± 4.3 | Family members confirmed with COVID-19 prior to children | Stay asymptomatic | Non symptoms, patchy, GGOs | Azithromycin, Oseltamivir, Arbidol, Traditional Chinese medicine | All patients were discharged |
| Yang et al. | 2020 | Case series | China | 23 | 11(33.3%) | 37 (26–45) | Not mentioned | Stay asymptomatic | Non symptoms. Images nor mentioned | No mentioned | No deaths reported |
SD= Standard deviation; IQR: interquartile range.