Generally speaking,deducted from the fundamental condition of our cases,we found that the severity of disease in our patients is relatively moderate.In addition,the affected age group is younger without so many underlying diseases.There are only 2 cases manifested as severe pneumonia,and one of them coverted from suspected case.By investigating the possible reasons,we speculated this consequence may cause by the delayed confirmation of infection.However,the condition seems to contradict the epidemiological study done by a cluster of Chinese researchers,in which they found that COVID-19 infection could cause severe respiratory illness similar to severe acute respiratory syndrome and was associated with ICU admission and high mortality.It may be due to the fact that the included are all imported cases who recently have gone to Wuhan or contacted with the identified cases,compared with those who were invaded directly by viruses.
PCR test has been widely used to confirm the viral infection targeted to the virus-specific nucleic acid sequences,but in our study,we found that after isolation for presumed infection of COVID-19,the 2 cases were finally diagnosed by repeated pharynx swabs tests.We postulated that maybe it caused by false sampling position,which means that the viruses are likely to exist in lower respiratory tract other than the upper.So the false-negative rate of PCR may mislead the clinical doctors and even miss the optimal opportunity for treatment. Some Chinese clinicians also found similar phenomenon and reported 5 cases.By evaluating radiographic characteristics of 5 patients with confirmed 2019-nCoV infection and initial negative or weakly positive RT-PCR,They found that the patients presented characteristic radiographic features of COVID-19 pneumonia from the first scan and then were confirmed by positive repeat swabs test during the isolated observation or treatment. They ascribed the possible reasons to laboratory error or insufficient viral material in the specimen.
In our cases,all of the conjunctival results of PCR were negative no matter in identified or suspected cases.We analyze and summarize the reasons as follows:(1)The shedding loads of the COVID-19 was below the sensitivity of the test or some individuals were actually not shedding viral DNA at that time.This opinion correlates with Sarrah E.Burr’s study,where she obtained 28 conjunctival swabs during the outbreak of acute haemorrhagic conjunctivitis in the Gambia,West Africa,caused by the epidemic of coxsackievirus,and 25% of the PCR-test showed negative results.(2)In our study,the conjunctival sampling time of the cases was after identification.The administration of drugs,such as corticosteroid and antiviral drugs,and the mutation of viruses could all affect the results.(3)The sensitivity of the viral nucleic acid kits is low.(4)The conjunctiva lacks of related receptors.A pivotal factor for efficient person-to-person transmission is the ability of the virus to attach to human cells.Because coronaviruses use a spike protein for attachment to host cells.As previously reported,both COVID-19 and SARS-nCov use the same receptor called ACE2,which has been verified to locate mainly on lung alveolar epithelial cells and enterocytes of the small intestine.However,whether ACE2 receptors exist on the conjunctival surface and the level of conjunctival ACE2 expression still need further investigation.Given that ACE2 expression is extremely rare on the ocular surface,the viruses could not attach to the conjunctiva and they may transfer to any organs in our bodies through lacrimal ductule. In our study,a 29-year-old female without any systematic disease converted to identified case from suspected case.She was a moderate suspected case,whose result of pharynx swab was positive at first,and after treatment,the result changed negative.However,the result represented as positive after 3 days.So we could speculate present therapies may only resist the viruses temporarily,and the COVID-19 may seek any opportunity to represent when the human immunity weakens.What’s worse,they may transfer to anywhere to find suitable hosts.In addition, we found that the sampling time contributed to obtain a reliable result,pharynx and conjunctiva swab should be collected meantime.In our study,the two swabs were obtained meantime in 3 identified cases,but the results were inconsistent.The coexistence of positive pharynx specimen and negative result of conjunctiva specimen reminded that the viruses may be more likely to attach to respiratory tract other than conjunctiva.
Restricted by reality,there are some limitations our study.Firstly,no positive result was obtained from identified and suspected cases .Secondly,we lack of swabs collected from individuals with normal eyes during the sampling process.