Since first reported in Wuhan, China, in late December 2019, the outbreak of the novel coronavirus now known as SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) has spread globally. 1e4 Serological dynamics of the infected persons remain scarce up to now. We report a case of coronavirus disease 2019 (COVID-19) after a travel return from Macau presenting as community-acquired pneumonia with the presence of SARS-CoV-2 IgG antibody at the second week of illness.
On February 5, 2020, a 46-year-old woman with underlying hypertension presented to the emergency department of a hospital in Tainan, Taiwan, with 2-day fever and cough referred from the outpatient clinic, 7 days after returning from Macau with a 4-day tour (January 21e24, 2020) with her husband and three children. The first confirmed case of the COVID-19 in Macau was announced on January 22, 2020. Given this travel history and progressive airway symptom, she was admitted to the isolation ward with appropriate personal protective equipment.
On examination, vital signs were within normal ranges, ear temperature 38 C, oxygen saturation 97% on room air, and respiratory rate 18 breaths per minute. However, she complicated of dyspnea on exertion. Laboratory investigations showed white blood cell count 4200 per mL (normal 3400e9500 per mL), platelet count 233,000 per mL (143,000e349,000 per mL), hemoglobin concentration 134 g/L (133e172 g/L), serum creatinine concentration 52 mmol/L (70e120 mmol/L), alanine aminotransferase 30 IU/L (<50 IU/L), and lactate 222 U/L (135e225 U/L). A chest radiograph showed patchy densities in the left upper Table 1 Clinical course, laboratory findings, and antimicrobial treatment of the case of COVID-19. and middle lung fields (Fig. 1A) . The patient received empiric oseltamivir and levofloxacin therapy for pneumonia. Throat swabs were negative for influenza virus A and B using polymerase chain reaction (PCR) method. SARS-CoV-2 was detected in a throat swab sample by real-time reverse-transcription PCR (RT-PCR) for E/RdRp1/RdRp2/N genes (cycle threshold value, 26.34) on hospital day 1 (February 5, 2020). A follow-up chest film at hospital day 14 (illness day 18) showed resolving patchy infiltrates (Fig. 1B) . The chest computed tomography at hospital day 26 showed no lesion at left upper lobe. Fever, cough, and dyspnea improved on hospital day 2 (Table 1) . With three consecutive negative results of real-time RT-PCR tests for SARS-CoV-2 in nasopharyngeal swab, she was discharged after 24 days of hospitalization. None of four members in the family had SARS-CoV-2 detected in their nasopharyngeal swabs sampled after 14 days' quarantine.
SARS-CoV-2 (ALLTEST 2019-nCoV IgG/IgM Rapid Test Cassette, Hangzhou ALLTEST Biotech Co., Ltd. Hangzhou, China) 5 was utilized for in vitro diagnosis and used to examine the presence of SARS-CoV-2 IgG antibody in seven serum samples (obtained on the hospital day 2, 3, 7, 9, 13, 20, and 23) from the patient. The SARS-CoV-2 IgG antibody was detected in five serum samples since the hospital day 7 (illness day 11, Table 1 ).
Now, the popular diagnostic confirmatory test for COVID-19 is the real-time RT-PCR. In contrast, the chronological dynamics of blood or serum antibodies in the cases of COVID-19 were not well evaluated. In China, a rapid lateral flow immunoassay using a recombinant antigen which is the receptor binding domain of SARS-CoV-2 spike protein to detect both IgM and IgG antibodies, was tested on 397 confirmed cases of COVID-19 and 128 control cases, and showed a promising testing sensitivity of 88.7% and specificity of 90.3%, when all of IgM and IgG positivity, only IgM positivity, and only IgG positivity, were regarded as positive testing results. 5 In comparison with real-time RT-PCR, the relative sensitivity, specificity, and accuracy rate of IgG detected by the kit we used, the ALLTEST 2019-nCoV IgG/ IgM Rapid Test Cassette, was claimed to be 100%, 98.0% and 98.6%, respectively. 6 However, this kit has been tested on serum samples from only 20 RT-PCR confirmed patients and 50 RT-PCR excluded patients and the relative sensitivity for anti-SARS-CoV-2 IgM antibody was 85% (95% CI, 62.1%e 96.8%). 6 Herein, only the testing results of anti-SARS-CoV-2 IgG antibody was shown (Table 1 ).
In conclusion, we reported that an initially healthy woman with COVID-19 which developed after Macau travel recovered without evident sequelae, in spite of chest radiographic abnormalities. With an evident travel exposure in this case, the incubation time could be reasonably estimated to be a period of 8e11 days and anti-SARS-COV-2 IgG appeared at post-exposure 18e21 days or the illness day 11. Of course, more serological data should be collected to elucidate the clinical and epidemiological utility of IgM/IgG measurements to detect symptomatic and asymptomatic cases of COVID-19.