Journal of Infection and Chemotherapy

The situation of the COVID-19 pandemic in Japan is drastically changing in the 2nd year, 2021, due to the appearance of SARS-CoV-2 variants of concern and the roll-out of mass vaccination. In addition to PCR diagnosis, periodic seroepidemiologic surveillance is important to analyze the epidemic situation. In this study, we analyzed the rate of seropositivity for the SARS-CoV-2 N and S antigens in Hyogo prefecture, Japan in August 2021. Sera collected from people who received a health check-up in a clinic of the Hyogo Prefecture Health Promotion Association were subjected to analysis of reactivity to the SARS-CoV-2 N and S antigens by electrochemiluminescence immunoassay (ECLIA) and enzyme-linked immunosorbent assay (ELISA), respectively. For a total 1,000 sera, the positive rates to N and S antigens were 2.1% and 38.7%, respectively. The infectious rate estimated by serological analysis based on the presence of the anti-N antibody was 2.5-fold higher than the value reported based on PCR-based analysis, and it increased five-fold compared to the rate determined by our previous seroepidemiologic study in October, 2020. The anti-S positive rate was almost consistent with the vaccination rate in this area. The observed high anti-S antibody level in the seropositive population may indicate that the mass vaccination in Japan is being performed smoothly at this time point, although the infectious rate has also increased.

The rapid diagnosis of Campylobacter infections is important for the management of infectious gastroenteritis. Although stool culture is considered the gold standard, its sensitivity is limited and it requires prolonged incubation times. We performed a prospective multicenter study at nine healthcare facilities in Japan to evaluate a Campylobacter rapid antigen test using stool specimens between March 2024 and August 2025. Patients with suspected infectious gastroenteritis were consecutively enrolled and tested using QuickNavi-Campylobacter and compared with the FilmArray Gastrointestinal Panel as the reference method. Discordant results were further evaluated by culturing and additional PCR assays. In total, 410 patients were included in the final analysis. The positive, negative, and total concordance rates between QuickNavi-Campylobacter and FilmArray Gastrointestinal Panel were 79%, 99%, and 93%, respectively. The positive concordance rate decreased in specimens collected [≥] 6 days after the onset of symptoms (50%). QuickNavi-Campylobacter demonstrated relatively good concordance with the FilmArray Gastrointestinal Panel in a real-world multicenter setting. These results suggest that this rapid antigen test may be particularly useful for the early diagnosis of suspected campylobacteriosis.

BackgroundIn the prolonged COVID-19 pandemic, there remains a high need for the development of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine that can be used more safely and effectively to prevents the disease onset or severe disease. To satisfy such unmet need, we are currently developing the inactivated whole particle SARS-CoV-2 vaccine (KD-414) and conducted a phase 2/3 study in healthy adults in Japan to accumulate more immunogenicity and safety data of KD-414 using the dose selected based on the results of the phase 1/2 study. MethodsIn an open-label uncontrolled phase 2/3 study, adults aged 18 years or older without a history of COVID-19 or COVID-19 vaccination received two intramuscular doses of KD-414 at a 28-day intervals, followed by one intramuscular dose 13 weeks after the second dose as the primary immunization. Safety data were collected after the first dose of KD-414 in all participants to evaluate the safety profile. In predetermined immunogenicity analysis subjects, the neutralizing antibody titers against the pseudovirus SARS-CoV-2 (Wuhan) before the first vaccination and after each vaccination with KD-414 were evaluated. ResultsA total of 2500 adults aged 18 years or older were enrolled; 2474 of them received the vaccination up to the second dose, and 2081 completed the third vaccination. Regarding the safety, no deaths or serious adverse reactions were recorded from the first vaccination until 28 days after the third vaccination with KD-414. The incidence of adverse reactions (number of participants with onsets/number of participants in the safety analysis set) was 80.6% (2015/2500). Adverse reactions with an incidence of 10% or more included injection site pain, malaise, headache, injection site erythema, myalgia, and injection site induration. A total of 11 events of grade 3 or higher adverse reactions that prevented daily activities in 9 participants. There was no increasing tendency in the incidence of adverse reactions responding to the vaccinations. To evaluate immunogenicity, 295 first comers enrolled from five age ranges were allocated to the immunogenicity analysis subjects; 291 participants received the vaccination up to the second dose, and 249 participants completed the third vaccination. The geometric mean titers (95% confidence interval [CI]) of neutralizing antibody titers against pseudovirus SARS-CoV-2 (Wuhan) 28 days after the second vaccination and 28 days after the third vaccination with KD-414 were 139.6 (118.9 - 164.0) and 285.6 (244.3 - 334.0), respectively, showing an approximately two-fold increase after the third vaccination compared to that after the second vaccination. The geometric mean titers (95% CI) of neutralizing antibody titers after the third vaccination were 327.6 (269.8 - 397.9), 272.2 (211.5 - 350.4) and 128.0 (51.6 - 317.7) in participants aged 18 to 40 years, 41 to 64 years, and 65 years or older, respectively, showing an age-dependency. ConclusionThis study confirmed the favorable safety profile of KD-414 as a result of three vaccinations of KD-414 administered to over 2000 healthy Japanese participants aged 18 years or older. There were no particular differences in the types and incidences of adverse reactions between vaccinations, and no tendency of an increase in adverse reactions with an increase in the number of vaccinations. Similar to the phase 1/2 study, neutralizing antibody responses appeared to be age-dependent and the highest titers were observed in the age group of 18 - 40 years. A phase 3 study in adults aged 18 - 40 years (jRCT2031210679) and a phase 2/3 study in children aged 6 months - 18 years (jRCT2031220032) are currently ongoing.

There are several recommendations for the use of personal protective equipment (PPE) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the selection of appropriate PPE for the current situation remains controversial. We measured serum antibody titers for SARS-CoV-2 in 10 participants who were engaged in the operation of charter flights for the evacuation of Japanese residents from Hubei Province. All participants wore PPE in accordance with Centers for Disease Control and Prevention guidelines. A total of 17 samples were tested, and all were seronegative. Hence, we conclude that the current PPE recommendation is effective to protect healthcare workers from SARS-CoV-2 infection.

The novel coronavirus disease 2019 (COVID-19) pandemic has spread rapidly worldwide. To prevent the spread of COVID-19, mRNA-based vaccines made by Pfizer/BioNTech (BNT162b1) and Moderna (mRNA-1273) have been widely used worldwide, including in Japan. Various adverse events after COVID-19 mRNA vaccinations have been reported, with differences observed among individuals. However, the analysis on the genetic background for susceptibility to side effects has been limited. In the present work, we performed genome-wide association studies (GWAS) for self-reported adverse events of COVID-19 mRNA vaccination in 4,545 Japanese individuals and identified 14 associated loci. Among these, 6p21 was associated with 37.5{degrees}C or higher fever, 38 {degrees}C or higher fever, and muscle pain. Our results may enable one to prepare for and manage side effects by knowing their susceptibility to the occurrence of adverse events. Furthermore, we obtained valuable data that can lead to the understanding of the mechanism of action of COVID-19 mRNA vaccines.

[Objective]Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody titers level and duration of elevated levels are considered important indicators for confirming the efficacy of coronavirus disease 2019 (COVID-19) vaccines. The objective of this study was to demonstrate the changes in antibody titers after the second and third doses of the COVID-19 vaccine, and to determine the antibody titers in cases of spontaneous infection with SARS-CoV-2 after vaccination. [Materials and Methods]From June 2021 to February 2023, IgG-type SARS-CoV-2 antibody titers were measured in 127 participants, including 74 outpatients and 53 staffs, at the Osaka Dental University Hospital (65 males and 62 females, mean age 52.3 {+/-} 19.1 years). [Results]Consistent with previous reports, the SARS-CoV-2 antibody titer decreased with time, not only after the second dose, but also after the third dose of the vaccine if there is no spontaneous COVID-19 infection. We also confirmed that the third booster vaccination was effective in increasing the antibody titer. 21 cases of natural infections were observed after administering two or more doses of the vaccine. 13 of these patients had post-infection antibody titers exceeding 40,000 AU/mL, and some cases continued to maintain antibody titers in the tens of thousands of AU/mL even after more than 6 months had passed since infection. [Conclusion]The rise in and duration of antibody titers against SARS-CoV-2 are considered important indicators for confirming the efficacy of novel COVID-19 vaccines. A longitudinal follow-up of antibody titers after vaccination in larger studies is warranted.

Japan has reported a small number of COVID-19 cases relative to other countries. Because not all infected people receive diagnostic tests for COVID-19, the reported number of COVID-19 cases must be lower than the actual number of infections. Assessments of the presence of antibodies against the spike protein of SARS-CoV-2 can retrospectively determine the history of natural infection and vaccination. In this study, we assessed SARS-CoV-2 seroprevalence by analyzing over 60,000 samples collected in Japan from February 2020 to March 2022. The results showed that about 5% of the Japanese population had been infected with the virus by January 2021. The seroprevalence increased with the administration of vaccinations to adults; however, among the elderly, it was not as high as the vaccination rate, probably due to poor immune responses to the vaccines and waning immunity. The infection was spread during the epidemic waves caused by the SARS-CoV-2 Delta and Omicron variants among children who were not eligible for vaccination. Nevertheless, their seroprevalence was as low as 10% as of March 2022. Our study underscores the low incidence of SARS-CoV-2 infection in Japan and the effects of vaccination on immunity at the population level.

The Japanese government has declared a national emergency and travel entry ban since the coronavirus disease 2019 (COVID-19) pandemic began. As of June 19, 2020, there have been no confirmed cases of COVID-19 in Iwate. Here, we analyzed the excess deaths as well as the number of patients and medical earnings due to the pandemic from prefectural hospitals located in one of the least-affected areas in Japan. From January to March 2020, the excess death rates per month were not significantly higher than the past-year average. Compared to January 2020, the numbers of both outpatients and inpatients in April 2020 showed a 5.2% and 6.1% decrease, respectively. Accordingly, the amount of medical earnings of both outpatients and inpatients in April 2020 showed a 3.0% and 6.3% decrease, respectively. Present analysis demonstrated that there were no excess deaths due to "unidentified" COVID-19 infections in Iwate; however, hospital budgetary management has been affected by the social restrictions. Regardless of COVID-19 infection spread, it may be difficult to maintain daily medical services if such low service activity continues in the existing hospitals. Additional longitudinal studies will be necessary to evaluate the effects of social restrictions on hospital management, but the true demand of regional medical services may emerge after this outbreak.

IntroductionVaccination programs are important to preventing COVID-19 infection. BNT162b2 is new type of vaccine, and previous studies have shown that the antibody response was significantly elevated in patients with prior COVID-19 infection after the first vaccination. However, no study has evaluated the efficacy of the vaccination or the adverse reactions of people with prior COVID-19 infection in Japan. The aim of this study is to evaluate the antibody titer and adverse reactions of BNT162b2 vaccine among participants with prior COVID-19 infection in Japan. MethodsThe data for this study was collected between April 15, 2021, and June 9, 2021. All of the hospital staff who received the BNT162b2 vaccine were included in this study and were sorted into either the prior infection group or the control group. We collected the data of adverse reactions through self-reporting and calculated the anti-SARS-CoV-2 spike-specific antibody titer for all participants. ResultsThe antibody titer of the prior-infection group in first antibody test was significantly higher than that of the control group in the second antibody test. There was no significant difference in adverse reactions between the prior infection group receiving its first vaccination and the control group receiving its second vaccination. ConclusionOur study shows that the antibody response following the first vaccination in the prior COVID-19 infection group was found to be comparable to that of the second vaccination in the control group; however, the evaluation of adverse reactions was inadequate and further, large-scale studies are needed.

Asymptomatic patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection must be quickly identified and isolated to prevent the spread of the virus. The number of asymptomatic healthy people is completely unknown because they remain untested. Detection of specific SARS-CoV-2 antibodies has been widely accepted as a diagnostic test, and an immunochromatographic test, which is simpler and relatively cheaper than other methods, is becoming the gold standard for identifying healthy people who had been infected with SARS-CoV-2 in the past. In this study, 1,528 volunteers who worked at a particular hospital were subjected to an immunochromatographic IgG test for SARS-CoV-2 to determine the ratio of asymptomatic people. Only 12 volunteers (0.79%) were IgG+, with no significant background differences in the sex, age, profession, experiences of working at the emergency department or caring for coronavirus disease 2019 patients. If this IgG+ ratio was to be extrapolated to Wakayama citys population, 2,780 out of 3,54,063 people may be asymptomatic for SARS-CoV-2. The results imply that anyone may get infected with SARS-CoV-2 but remain asymptomatic.

The prevalence of asymptomatic SARS-CoV-2 infection in healthcare workers with intensive exposure to COVID-19 is unclear. In this study, we investigated the seroprevalence of SARS-CoV-2 in 797 asymptomatic healthcare workers with intensive exposure to COVID-19 patients in Wuhan, China. Positive IgG was detected from 35 asymptomatic healthcare workers, and the prevalence of antibodies to SARS-CoV-2 in asymptomatic healthcare workers was 4.39% (35/797). None of them developed COVID-19 until May 15. 33 of them have performed at least one chest CT scan showing no viral pneumonia features, and 16 have finished at least one-time SARS-CoV-2 RNA detection with negative results. When contacting with the patients, 15 of them dressed with full personal protective equipment (PPE), and 16 worn N95 mask and gown. To the best of our knowledge, this is the first investigation reported that the seroprevalence of SARS-CoV-2 was 4.39% in asymptomatic healthcare workers with applied PPE in a high epidemic area, which may provide useful information of estimating asymptomatic infection rate in general population.

The exact pathology of COVID-19 remains mostly unclear, and accurate epidemiological understanding and rapid testing are crucial to overcome this disease. Several types of nucleic acid tests (NAT) have been used in Japan, but information about the viral RNA load, determined by Ct values, of the patients is limited due to the small number of patients tested in each clinical institution and lack of standardization of the testing kits. We have been performing the qRT-PCR tests established by NIID, and the mean Ct value distribution of 62 cases, which are deemed "first-visit" patients, among the total of 88 positive cases tested in a 4-day window of early April, was 24.9 with SD=5.45. Recently approved antigen testing kits were also used in the same samples (62 positives) along with 100 negative cases, and it revealed the positive predictive value of 80.6% and negative predictive value of 100%, with an overall agreement rate of 92.6%. These results indicate that a certain number of patients with lower Ct values, existed in Japan when SARS-CoV-2 virus started to spread. The newly approved rapid antigen testing kit will be a useful tool to identify such populations rapidly.

Much of the current literature on the adverse effects occurring after the coronavirus disease-2019 (COVID-19) vaccination focused on serious adverse events (AEs). Consequently, the non-serious AEs have yet to be comprehensively elucidated. This study aims to investigate the incidence rate and risk of non-serious AEs including gynecological, hematological, dermatological, ophthalmological, otologic, and dental problems following the COVID-19 vaccination. We conducted a population-based cohort study was conducted with the National Health Insurance Service (NHIS) database in Seoul, South Korea. The cumulative incidence rate (cIR) per 10,000 population, Odds ratio, and Hazard ratio (HR) with a 95% Confidence Interval (CI) were measured to assess the non-serious AEs, as reported by the Vaccine Adverse Event Reporting Center, after COVID-19 vaccination. The cIR of non-serious AEs for three months was significantly higher in vaccinated subjects than in non-vaccinated subjects, except for endometriosis. The vaccination significantly increased the risks of all the non-serious AEs except for visual impairment. The risk of inner ear disease showed the highest HRs (HR [95% CI] = 2.37 [2.15-2.60]) among the non-serious AEs following COVID-19 vaccination. Among the vaccinated subjects, heterologous vaccination was associated with the increased risk of most of the non-serious AEs. The three-month risks of incidental non-serious AEs are substantially higher in the COVID-19 vaccinated subjects than in non-vaccinated controls. Our findings suggested that vaccinated subjects with predisposition are potentially vulnerable to the occurrence of broad-spectrum AEs although the COVID-19 vaccines may not be serious.

PurposeTo estimate the effectiveness of an Epstein-Barr virus (EBV) serology-based screening program to reduce nasopharyngeal carcinoma (NPC) mortality in a cluster randomized controlled trial in an NPC high-risk population. MethodsSixteen towns in Sihui and Zhongshan Cities, China were selected; eight were randomly allocated to the screening group and eight to the control group. Cantonese residents aged 30-69 years with no history of NPC were included January 1, 2008 to December 31, 2015. Residents in the screening towns were invited to undergo serum EBV VCA/EBNA1 IgA antibody tests; others received no intervention. Screening lasted through December 31, 2015; the population was followed through December 31, 2017. ResultsA total of 175,037 residents in the screening group and 184,526 residents in the control group were included. NPC incidence was similar in screening and control groups. A 28% reduction in NPC mortality was observed in the screening versus control arms in the overall study population (8.0 NPC deaths per 1000 person years versus 11.1; adjusted rate ratio [aRR]=0.72; 95% confidence interval=0.48-1.09; p=0.12). A stronger benefit was observed among individuals aged >50 (aRR=0.63; p=0.048) compared to those <50 (aRR 0.93; p=0.75). The reduction was increased among individuals from towns randomized to screening who participated in the screening program (aRR=0.38, p=0.001). ConclusionIn this near 10-year trial, serology EBV VCA and EBNA1 IgA antibody testing led to a reduction in NPC mortality, particularly among individuals aged [&gt;=]50. EBV antibody-based screening for NPC is effective at reducing NPC mortality in high-risk populations. Trial registration numberNCT00941538

BackgroundSince December 2019, Severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)-infected disease (Coronavirus Disease 2019,COVID-19) emerged in Wuhan, China,and rapidly spread throughout China,even throughout the world. We try to describe the epidemiological and clinical characteristics of COVID-19 in non-Wuhan area,and explore its effective treatment. MethodsRetrospective, single-center case series of the 51 hospitalized patients with confirmed COVID-19 at Chongqing University Three Gorges Hospital in Chongqing, China, from January 20 to February 3, 2020;The discharge time was from January 29 to February 11, 2020. The main results and indicators of epidemiology, demography, clinical manifestation, laboratory examination, imaging data and treatment data of 51 patients with covid-19 were collected and analyzed. The changes of blood routine and biochemical indexes at discharge and admission were compared. Compare the clinical characteristics of severe patients (including severe and critical patients) and non-severe patients (general patients). ResultsOf 51 hospitalized patients with COVID-19, the median age was 45 years (interquartile range, 34-51; range, 16-68 years) and 32 (62.7%) were men.43(84.3%) patients had been to Wuhan or Other Hubei areas outside Wuhan,and 4(7.7%) patients had a clear contact history of COVID-19 patients before the onset of the disease, and 4 (7.7%) patients had no clear epidemiological history of COVID-19.Common symptoms included fever (43 [84.3%]), cough (38 [74.5%]) and fatigue (22 [43.1%]). Lymphopenia was observed in 26 patients (51.0%), and elevated C-reactive protein level in 32 patients (62.7%). Ground-glass opacity was the typical radiological finding on chest computed tomography (41 [80.4%]),Local consolidation of pneumonia in some patients(17 [33.3%]).Most of the patients were treated with traditional Chinese medicine decoction (28 [54.9%]),all of them received aerosol inhalation of recombinant human interferon a-1b for injection and oral antiviral therapy with Lopinavir and Ritonavir tablets (51 [100%]); Most of the patients were given Bacillus licheniformis capsules regulated intestinal flora treatment (44 [86.3%]). 10 patients (19.6%) received short-term (3-5 days) glucocorticoid treatment. Compared with non-severe patients (n = 44), severe patients (n = 7) were older (median age, 52 years vs 44 years), had a higher proportion of diabetes mellitus (4 [57.1%] vs 0 [0.0%]), most of them needed antibiotic treatment (7 [100%] vs 4 [9.1%], most of them needed nutritional diet (6 [85.7%) vs 0 [0.0%], and were more likely to have dyspnea (6 [85.7%] vs 5 [11.4%]),most of them needed noninvasive mechanical ventilation (6 [85.7%] vs 0 [0.0%]). Except one patient died, the remaining 50 patients were discharged according to the discharge standard, the common clinical symptoms disappeared basically, the lymphocyte increased significantly (P=0.008), CRP decreased significantly (P <0.001). The median length of stay was 12 days (IQR, 9-13). ConclusionIn 51 single center cases confirmed as COVID-19 and discharged from the hospital, 13.7% of the patients were severe. The main clinical symptoms of patients with COVID-19 were fever, cough and asthenia,Some patients had obvious dyspnea. They had clinical laboratory and radiologic characteristics. There is no specific drug treatment for the disease. For the treatment of COVID-19, in addition to oxygen inhalation and antiviral treatment, attention should be paid to the dialectical treatment of traditional Chinese medicine, regulation of intestinal flora, nutritional support treatment and other comprehensive treatment.

The total number of COVID-19 patients since the outbreak of this infection in Wuhan, China has reached 40000 and are still growing. To facilitate triage or identification of the large number of COVID-19 patients from other patients with similar symptoms in designated fever clinics, we set to identify a practical marker that could be conveniently utilized by first-line health-care workers in clinics. To do so, we performed a case-control study by analyzing clinical and laboratory findings between PCR-confirmed SARS-CoV-2 positive patients (n=52) and SARS-CoV-2 negative patients (n=53). The patients in two cohorts all had similar symptoms, mainly fever and respiratory symptoms. The rates of patients with leukocyte counts (normal or decreased number) or lymphopenia (two parameters suggested by current National and WHO COVID-19 guidelines) had no differences between these two cohorts, while the rate of eosinopenia (decreased number of eosinophils) in SARS-CoV-2 positive patients (79%) was much higher than that in SARS-CoV-2 negative patients (36%). When the symptoms were combined with eosinopenia, this combination led to a diagnosis sensitivity and specificity of 79% and 64%, respectively, much higher than 48% and 53% when symptoms were combined with leukocyte counts (normal or decreased number) and/ or lymphopenia. Thus, our analysis reveals that eosinopenia may be a potentially more reliable laboratory predictor for SARS-CoV-2 infection than leukocyte counts and lymphopenia recommended by the current guidelines.

BackgroundLittle is known about the population prevalence of antibodies against emerging immune escape variants of SARS-CoV-2. MethodsA population-based prevalence study was conducted in Yokohama City, the most populous municipality of Japan. Quantitative measurements of immunoglobulin G against SARS-CoV-2 spike protein (SP-IgG) and qualitative measurements of neutralization antibodies against the Omicron BA.1 and BA.2 variants were performed. ResultsOf 6,000 randomly selected residents aged 20-74, 1,277 participated in the study during a period from January 30 to February 28, 2022. Of them, 3% had prior diagnosis of COVID-19, 96% received at least two-doses of SARS-CoV-2 vaccines, and 94% were positive for SP-IgG. The positive rates of neutralizing antibodies were 28% to Omicron BA.1 and BA.2 variants in a random sample of 10% of participants (n=123) and 100% to BA.1 and BA.2 among participants who received the third vaccination at least 7 days before (n=66). ConclusionsIn this population-based prevalence study in Japan, most had SP-IgG antibodies but the overall neutralizing antibody positive rate was 28% against the Omicron BA.1 and BA.2 variants. The population-level insufficient humoral immunity against the Omicron variants may explain the outbreak of COVID-19 during this period in Japan.

Serological evaluation with SARS-CoV-2 specific IgG antibody will be an alternative way to know the pandemic of novel coronavirus disease (COVID-19) if the capacity for diagnostic PCR test is limited. The point-of-care test to detect SARS-CoV-2 specific IgG antibody in peripheral blood (n =202) was performed in two community clinics in Tokyo, Japan. The overall positive rate of SRAS-CoV-2 IgG antibody was 5.9% (95% confidence interval[CI]: 3.1-10.1). Higher rate was observed for healthcare workers (n =55, 9.1 [3.0-20.0]). The limitation on antibody tests includes low sensitivity and potent cross-reactivity with the previous coronavirus. Robust healthcare policy to efficiently monitor COVID-19 spread is warranted in Tokyo.

In China, the patients with previously negative RT-PCR results again test positive during the post-discharge isolation period. We aimed to determine the clinical characteristics of these "recurrent-positive" patients. We retrospectively reviewed the data of 15 recurrent-positive patients and 107 control patients with non-recurrent, moderate COVID-19 treated in Wuhan, China. Clinical data and laboratory results were comparatively analyzed. We found that recurrent-positive patients had moderate disease. The rate of recurrent-positive disease in our hospital was 1.87%. Recurrent-positive patients were significantly younger (43(35-54) years) than control patients (60(43-69) years) (P=0.011). The early LOS (length of stay in hospital before recurrence) was significantly longer in recurrent-positive patients (36(34-45) days) than in control patients (15(7-30) days) (P =0.001). The time required for the first conversion of RT-PCR results from positive to negative was significantly longer in recurrent-positive patients (14(10-17) days) than in control patients (6(3-9) days) (P =0.011). Serum COVID-19 antibody levels were significantly lower in recurrent-positive patients than in control patients (IgM: 13.69 {+/-} 4.38 vs. 68.10 {+/-} 20.85 AU/mL, P = 0.015; IgG: 78.53 {+/-} 9.30 vs. 147.85 {+/-} 13.33 AU/mL, P < 0.0001). Recurrent-positive patients were younger than control patients. The early LOS (length of stay in hospital before recurrence) was significantly longer in recurrent-positive group than that in control group. COVID-19 IgM/IgG antibody levels were significantly lower in recurrent-positive group than those in control group, which might explain why the virus RNA RT-PCR was positive after the initial "clinical cure"(with three times of virus RNA RT-PCR negative). The virus might not be fully eliminated because of the lower IgG level and their later replicating might result in recurrent-positive virus RNA RT-PCR.

ObjectiveThis study attempted to explore the difference of clinical characteristics in H1N1 influenza infection and SARS-CoV-2 Omicron infection in people younger than 65 years old, in order to better identify the two diseases. MethodsA total of 127 H1N1 influenza patients diagnosed from May 2009 to July 2009 and 3265 patients diagnosed and identified as SARS-CoV-2 Omicron BA.2 variant from March 2022 to May 2022 were admitted in this study. Through the 1 : 2 match based on age (The difference is less than 2 years), gender and underlying diseases, 115 patients with H1N1 infection and 230 patients with SARS-CoV-2 Omicron BA.2 infection(referred to as H1N1 group and Omicron group) were included in the statistics. The clinical manifestations of H1N1 group were compared with those of Omicron group. Logistic regression was performed to analyze the possible independent risk factors of H1N1 group and Omicron group. And multiple linear regression was used to analyze the factors for time for nucleic acid negativization (NAN). ResultsThe median age of the two groups was 21 [11,26] years. Compared with the H1N1 group, the Omicron group had lower white blood cell count and CRP levels, less fever, nasal congestion, sore throat, cough, sputum and headache, while more olfactory loss, muscle soreness and LDH abnormalities. The Omicron group used less antibiotics and antiviral drugs, and the NAN time was longer (17 [14,20] VS 4 [3,5], P < 0.001). After logistic regression, it was found that fever, cough, headache, and increased white blood cell count were more correlated with the H1N1 group, while muscle soreness and LDH abnormalities were more correlated with the Omicron group. After analyzing the factors of NAN time, it was found that fever (B 1.529, 95 % CI [0.149,2.909], P = 0.030) significantly predicted longer NAN time in Omicron patients. ConclusionThis study comprehensively evaluated the similarities and differences in clinical characteristics between SARS-CoV-2 Omicron infection and 2009 H1N1 influenza infection, which is of great significance for a better understanding for these diseases.