According to the data released by Hainan Health Commission [11], by Mar 24, 2020, 162 of 168 patients had been discharged, 6 patients died, with the mortality rate of 3.6%. No new cases occurred from Feb 19, 2020 [14]. The 91 cases in study accounted for 54.2% of all the confirmed cases in Hainan, with similar trend in epidemic course (see Fig. 1). Of the 91 patients, three patients died. The mortality was 3.3%, which also similar to that of the whole Hainan province.
Our study shows that during the 29-day epidemic period, most of the patients were diagnosed within the first three weeks after the first identified imported case. In the early period, imported cases were predominant. In the later period, local cases were more common and 77.1% of the patients appeared clustering, mainly in families. However, the local cases did not lead to continuous community transmission, reflected by the short epidemic period (29 days). This may be attributed to the effective implementation of prevention and control policies and self-protection awareness of the public in Hainan (Fig. 1). The measures include establishing fever clinic for screening suspicious patients, designating hospitals focusing on treating patients with COVID-19 [17], raising the level of emergency response to COVID-19 prevention and control to first level promptly at Day 4. At the same time, other measures also work well for blocking the routes of transmission and reducing the chance of infection. For examples, encouraging the public to wear face masks, wash hands more frequently, and stay at home unless necessary, activating joint prevention and control mechanism, cross-sectors control for traffic control at community level. Moreover, delaying the resumption of work and school, implementing work-from-home for employee and online teaching for students were adopted to reduce the probability of cluster [18]. The reported estimate incubation time of the SARS-CoV‐2 was based on limited data. Zhong reported the median incubation period was 4 days in 291 cases in China [19]. Jiang Xu et al. find there is no observable difference between the incubation time for SARS‐CoV‐2, severe acute respiratory syndrome coronavirus (SARS‐CoV), and middle east respiratory syndrome coronavirus (MERS‐CoV), with a mean of 4.9 days for SARS‐CoV‐2, 4.7 days for SARS, and 5.8 days for MERS [20]. To avoid the risk of virus spread, all potentially exposed subjects are required to be isolated for 14 days, which is the longest predicted incubation time. Our epidemiological investigation for 53 patients from Wuhan found that the median time of symptom onset was 5 days, with a range of 1 day to 34 days. The patient with the longest incubation period, a male in their 70’s, flew from Wuhan to Hainan on January 2, 2020 and had no contact with confirmed or suspected COVID-19 patients. He occasionally went to the farmers' market near his residence to buy vegetables, but there were no confirmed COVID-19 patients associated with the market. He developed symptoms on February 5 and was diagnosed on February 7, 2020 [11]. This particular case indicates that the longest incubation time may be more than 34 days.
This study showed the main symptoms of the patients in Hainan Province were fever, cough, and 30% of the patients had shortness of breath. Compared with early COVID-19 cases in Wuhan, diarrhea (14.3%) was relatively more common in Hainan patients [21]. 15 (16.5%) patients were severe, 12 of them were imported cases and three were local cases. The main complications include infections and ARDS. Six severe cases developed to MODS. In general, the proportion of severe patients and mortality are lower than that of Wuhan and similar to the national data [22, 23].
In the imported cases, the proportion of patients with fever, the peak temperature, the level of blood CRP, the proportion of severe cases, and the incidence of complications, especially infections, were higher than those in the local cases. Meanwhile, the lymphocyte and platelets counts were significantly lower in imported cases than that of local ones. Data showed imported cases were older and coexisting illness was more common than the local ones, which might demonstrate why the imported ones are severer. Another possible explanation is that the time of infecting SARA-CoV-2 in imported cases is earlier, with a more virulent virus subtype. However, this requires further study of genomic and pathogenicity of SARA-CoV-2 at different stages of transmission. Tang's research indicates that the SARS-CoV-2 had formed two subtypes of S and L during the transmission process, and changes in viral genes will cause changes in its pathogenicity and transmission [24]. The similar study had been corroborated in the study of the MERS virus, which had shown that the virus becomes weaker during transmission [25]. It remains to be further studied whether there is virus mutation in the process of virus transmission from imported cases to local cases, which may lead to the weakening of its pathogenicity.
All 91 patients, including four asymptomatic patients, had CT changes in the lungs, which mainly manifested as ground-glass opacity in lung periphery at early stage. However, as the disease progressed, some patients had pulmonary consolidation and pleural effusion. Therefore, pulmonary CT examination is a sensitive indicator for the screening of COVID-19 and is recommended for all suspected patients [26].
Even so, SARS-CoV-2 RNA is the direct evidence for confirming COVID-19. Among all our patients, SARS-COV-2 RNA were detected in nasopharyngeal swab, but RNA was not detected in 12 patients’ feces. Due to the positive detecting of SARS-CoV-2 RNA in feces, the problem of gastrointestinal transmission and even aerosol transmission has attracted broad attention. Since then, multiple research teams have isolated viruses in the feces, further illustrating the risk of gastrointestinal transmission. However, for a new viral infectious disease, there is no exact data on how long virus would be shed through respiratory and digestive tract. Our study found that the median duration of fecal SARS-CoV-2 shedding was longer than that in nasopharyngeal swabs, which was 19 and 16 days, respectively. And the longest time of SARS-CoV-2 RNA persistent positive and viral shedding were 40 days and 43 days, respectively. The relative long virus shedding duration could impose great challenge for health system as the patient pool flows slow and taking up substantial health facility. While it is impossible to host all positive cases in hospitals throughout the virus shedding period, it is possible to shift less acute cases to other temporary facilities like Wuhan. It is worth noting that the nasopharyngeal swabs and feces collected on the day of death of the three critically ill patients were still positive. This suggests that the persistence of the virus may have an impact on disease prognosis, and it is urgent to screen and develop effective antiviral drugs.
Unfortunately, until now, there are no effective antiviral drugs. Drugs such as remdesivir, kaletra, arbidol, chloroquine phosphate and some Chinese traditional medicine have shown certain effects, but still lack of rigorous and proven evidence [27–30]. Clinical trials of these drugs are currently ongoing. Treatment of all our patients was basically based on the interferon alpha nebulization, plus the antiviral regimen of arbidol or kaletra. However, without controlled study, it is difficult to determine whether it is the natural fluctuation of the virus replication or the effect of the drug.
There are some limitations in this study: Due to the barriers to data collection, clinical data of all 168 patients in the entire Hainan Province have not been collected.