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As the worst yellow fever epidemic occurred in Angola in 2016, yellow fever cases had been discovered firstly in China in the history, which raising great public concern in domestic and international societies. The epidemiological characteristics of the total eleven yellow fever cases were analyzed. The results showed that all imported cases came from Angola, and they were identified in the 11th to 15th week of 2016, 1-2 weeks after the peak of the Angolan epidemic. Eight cases had once visited the same local Chinese medicine hospital in Angola. Expect for one death, all other 10 cases had recovered after timely and proper treatment. The results suggested that although China has taken effective response to the imported epidemic of yellow fever, several problems on cases information sharing, health education were still exposed, which might also be obstacles for reducing the imported risk of other foreign infectious diseases for China. This study summarize the experiences learned from 2016, with the hope of providing experiences on prevention and control to other diseases.

Summary COVID-19 was declared a pandemic by WHO on March 11, 2020, the first non-influenza pandemic, affecting more than 200 countries and areas, with more than 5·9 million cases by May 31, 2020. Countries have developed strategies to deal with the COVID-19 pandemic that fit their epidemiological situations, capacities, and values. We describe China's strategies for prevention and control of COVID-19 (containment and suppression) and their application, from the perspective of the COVID-19 experience to date in China. Although China has contained severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and nearly stopped indigenous transmission, a strong suppression effort must continue to prevent re-establishment of community transmission from importation-related cases. We believe that case finding and management, with identification and quarantine of close contacts, are vitally important containment measures and are essential in China's pathway forward. We describe the next steps planned in China that follow the containment effort. We believe that sharing countries' experiences will help the global community manage the COVID-19 pandemic by identifying what works in the struggle against SARS-CoV-2.

Imported infectious diseases are becoming a serious public health threat in China. However, limited information concerning the epidemiologic characteristics of imported infectious diseases is available. In this study, we collected data related to imported infectious diseases in mainland China from the National Information Reporting System of Infectious Diseases and analyzed demographic, temporal, and spatial distributions. The number of types of imported infectious diseases reported increased from 2 in 2005 to 11 in 2016. A total of 31,740 cases of infectious disease were imported to mainland China during 2005-2016; most of them were found in Yunnan Province. The cases were imported mainly from Africa and Asia. As a key and effective measure, pretravel education should be strengthened for all migrant workers and tourists in China, and border screening, cross-border international cooperation, and early warning should be further improved.

Human infections with influenza H7 subtypes, such as H7N9, have raised concerns worldwide. Here, we report a human infection with a novel influenza A(H7N4) virus. A 68 years-old woman with cardiovascular and cholecystic comorbidities developed rapidly progressed pneumonia with influenza-like-illness as initial symptom, recovered after 23 days-hospitalization including 8 days in ICU. Laboratory indicators for liver and blood coagulation dysfunction were observed. Oseltamivir phosphate, glucocorticoids and antibiotics were jointly implemented, with nasal catheterization of oxygen inhalation for this patient. We obtained the medical records and collected serial respiratory and blood specimens from her. We collected throat, cloacal and/or feces samples of poultry and wild birds from the patient’s backyard, neighborhood, local live poultry markets (LPMs) and the nearest lake. All close contacts of the patient were followed up and sampled with throat swabs and sera. Influenza viruses and other respiratory pathogens were tested by real-time RT-PCR, viral culturing and/or sequencing for human respiratory and bird samples. Micro-neutralizing assay was performed for sera. A novel reassortant wild bird-origin H7N4 virus is identified from the patient and her backyard poultry (chickens and ducks) by sequencing, which is distinct from previously-reported avian H7N4 and H7N9 viruses. At least four folds increase of neutralizing antibodies to H7N4 was detected in her convalescent sera. No samples from close contacts, wild birds or other poultry were tested positive for H7N4 by real-time RT-PCR.

Background The first human infections of novel avian influenza A(H7N9) virus were identified in China in March 2013. Sentinel surveillance systems and contact tracing may not identify mild and asymptomatic human infections of influenza A(H7N9) virus. Objectives We assessed the seroprevalence of antibodies to influenza A(H7N9) virus in three populations during the early stages of the epidemic. Patients/Methods From March 2013—May 2014, we collected sera from the general population, poultry workers and contacts of confirmed infections in nine Chinese provinces reporting human A(H7N9) infections and, for contacts, second sera 2-3 weeks later. We screened for A(H7N9) antibodies by advanced hemagglutination inhibition (HI) assay and tested sera with HI titers ≥20 by modified microneutralization (MN) assay. MN titers ≥20 or four-fold increases in paired sera were considered seropositive. Results Among general population sera (n=1480), none were seropositive. Among poultry worker sera (n=1866), 28 had HI titers ≥20; two (0.11%, 95% CI: 0.02%-0.44%) were positive by MN. Among 61 healthcare and 117 non-healthcare contacts’ sera, five had HI titers ≥20, and all were negative by MN. There was no seroconversion among 131 paired sera. Conclusions There was no evidence of widespread transmission of influenza A(H7N9) virus during March 2013 to May 2014, although A(H7N9) may have caused rare, previously unrecognized infections among poultry workers. Although findings suggest there were few undetected cases of influenza A(H7N9) early in the epidemic, it is important to continue monitoring transmission as virus and epidemic evolve. This article is protected by copyright. All rights reserved.

Since human infections with avian influenza A(H7N9) virus were first reported by the Chinese Center for Disease Control and Prevention (China CDC) in March 2013 (1), mainland China has experienced four influenza A(H7N9) virus epidemics. Prior investigations demonstrated that age and sex distribution, clinical features, and exposure history of A(H7N9) virus human infections reported during the first three epidemics were similar (2). In this report, epidemiology and virology data from the most recent, fourth epidemic (September 2015-August 2016) were compared with those from the three earlier epidemics. Whereas age and sex distribution and exposure history in the fourth epidemic were similar to those in the first three epidemics, the fourth epidemic demonstrated a greater proportion of infected persons living in rural areas, a continued spread of the virus to new areas, and a longer epidemic period. The genetic markers of mammalian adaptation and antiviral resistance remained similar across each epidemic, and viruses from the fourth epidemic remained antigenically well matched to current candidate vaccine viruses. Although there is no evidence of increased human-to-human transmissibility of A(H7N9) viruses, the continued geographic spread, identification of novel reassortant viruses, and pandemic potential of the virus underscore the importance of rigorous A(H7N9) virus surveillance and continued risk assessment in China and neighboring countries.

Word Health Organizaiton has declared the clusters of microcephaly cases and other neurological disorders constituted a Public Health Emergency of International Concern on 1 Feberuary 2016, and there is increasing evidence that they are causal related with Zika virus. Zika virus disease has been identified in 41 countires and areas since 2015, and it is spreading to the other parts of the world. There were 10 imported cases of Zika virus disease detected in the mainland of China from January to February 2016, without autochthonous transmission.

To the Editor: Zika virus, a member of the Flaviviridae family, is primarily transmitted through Aedes spp. mosquitoes, and evidence of vertical, sexual, and blood transmission of Zika virus has been reported (1–3). The virus has spread rapidly across Latin America and the Caribbean since the end of 2014 and has been linked to an increase in neurologic disorders and neonatal malformations in these areas (4). Zika virus has the potential to spread internationally through the carriage of goods and travelers (5). Traveler volume between China and areas with autochthonous transmission of Zika virus is increasing; in 2015, China received ≈84,000 travelers who had departed from international airports in Brazil (5). The Ae. aegypti mosquito, the competent vector for Zika virus, is found in areas of Hainan, Guangdong, and Yunnan provinces on the mainland of China, where the known distribution is limited to areas below 22° latitude. However, Ae. albopictus mosquitoes are widely distributed, extending from the southern reaches to the northern and western parts of China, with north fringes from Shenyang in Liaoning Province, through Tianshui and Longnan in Gansu Province, to Motuo in Tibet (6). Surveillance of Zika virus infection among Chinese travelers has been enhanced since January 2016. We report the clinical and laboratory findings for a case Zika virus infection imported from Venezuela. A previously healthy 34-year-old Chinese man was admitted to the Hospital of Ganxian on February 6, 2016. He had worked in Caracas, Venezuela, during January 1–February 2 and had onset of fever (38.0°C), headache, and dizziness on January 28. He subsequently had rash, chills, retro-orbital pain, and mild diarrhea on February 2, the day on which he departed from Caracas and traveled to Jiangxi Province via Paris and Hong Kong, arriving in Shenzhen, China, on February 5. At the time of hospital admission, the patient had fever (36.7°C), headache, conjunctivae, rash on his back and face, retro-orbital pain, and mild diarrhea. General clinical examination was unremarkable. Results of a complete blood cell count and liver function tests were within reference ranges. Serum samples were collected at day 9 and day 10 after symptom onset, and urine samples were collected once a day from day 10 through day 14. In the 2 serum samples, no dengue virus (DENV) or chikungunya virus (CHIKV) IgM or IgG were detected by a Panbio IgM and IgG capture ELISA for DENV (Panbio, Queensland, Australia) or by an indirect immunofluorescence assay slide test kit for CHIKV (EUROIMMUN AG, Lubeck, Germany). Serum and urine samples were negative for DENV nonstructural protein 1 (NS1) antigen on an NS1-ELISA test kit (Wantai Bio-Pharm, Beijing, China). To detect virus RNA in samples, in-house–designed probe and primers specific to DENV and CHIKV were used (7). The PCR for Zika virus was targeted to the NS1 gene. RNA was extracted from 140 μL of serum or urine by using the QIAamp Viral RNA Mini Kit (QIAGE, Hilden, Germany). Amplification reactions were performed by using the AgPath-ID One-Step RT-PCR Kit (Ambion, Carlsbad, CA, USA). A standard curve with serial dilutions of known concentrations of in vitro–transcribed RNA from a reference plasmid was used to estimate viral load in samples. Test results for DENV and CHIKV were negative. However, the serum sample collected at day 9 was positive for Zika virus RNA (viral load 1.4 × 104 copies/mL), and Zika virus RNA was detected from urine samples collected on days 10, 11, and 12 (viral loads 8.6 × 104, 4.5 × 104, and 1.2 × 104 copies/mL, respectively). Next-generation genomic sequencing of the Zika virus genome was conducted by using the MiSeq platform (Illumina, Hayward, CA, USA) on serum and urine samples. A 1,813-bp of partial genome sequences (strain VE_Ganxian, GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"KU740199","term_id":"998963116","term_text":"KU740199"}}KU740199) was obtained from urine and was used for comparing with selected other strains from GenBank. Phylogenetic analysis showed that the virus was of Asian lineage (Figure). Pairwise genetic distance calculation indicated that the sequence was most closely related to other viruses reported from French Polynesia in 2013 (strain H/PF/2013), the Caribbean in 2014 (strain Haiti/1225/2014), and Latin America in 2015 (strain ZikaSPH2015), having a 99.4% similarity in sequence. Figure Phylogenetic analysis of partial sequences of Zika virus for an imported case of Zika virus infection in a traveler returning to China from Caracas, Venezuela, February 2016, compared with selected other strains from GenBank. A) Schematic diagram showing ... The clinical findings for the patient were similar to those previously reported among Zika virus–infected patients (9), although no arthralgia was apparent. Viral RNA remained detectable for 9 days after symptom onset in serum and for an additional 3 days in urine. We did not test this patient’s semen and thus cannot comment on risk for onward sexual transmission; however, the patient was told about the risks for sexual transmission of Zika virus and was advised to adopt safer sexual practices or to abstain from sexual activity for at least 1 month after recovery. In February, the mosquito density is low in Jiangxi Province (10), suggesting that this imported case is unlikely to cause mosquitoborne transmission. However, with the onset of summer and increased density of Aedes mosquitos, the risk for onward transmission of travel-associated Zika virus should not be overlooked.

To detect changes in human-to-human transmission of influenza A(H7N9) virus, we analyzed characteristics of 40 clusters of case-patients during 5 epidemics in China in 2013-2017. Similarities in number and size of clusters and proportion of clusters with probable human-to-human transmission across all epidemics suggest no change in human-to-human transmission risk.

Since the first outbreak of avian influenza A(H7N9) virus in humans was identified in 2013, there have been five seasonal epidemics observed in China. An earlier start and a steep increase in the number of humans infected with H7N9 virus was observed between September and December 2016, raising great public concern in domestic and international societies. The epidemiological characteristics of the recently reported confirmed H7N9 cases were analysed. The results suggested that although more cases were reported recently, most cases in the fifth epidemic were still highly sporadically distributed without any epidemiology links; the main characteristics remained unchanged and the genetic characteristics of virus strains that were isolated in this epidemic remained similar to earlier epidemics. Interventions included live poultry market closures in several cities that reported more H7N9 cases recently.

On the Internet, there is a lot of open access information related to infectious diseases, e.g., official announcement, media news, bulletin boards, blogs, and other social media. If proper data retrieval and screening methods were applied on these Internet-based data, it would be very useful to improve the timeliness of early detection for infectious diseases. In China, we practice early warning using Internet-based data with routine intelligence screening assessment every day, and respond to any unusual event in a timely manner. Through this mechanism, the surveillance and early warning of Internet-based data for infectious disease and public health emergency plays an important supplemental role to the traditional surveillance systems.

This chapter describes how the surveillance department conducts investigation and verification, risk assessment, and takes necessary public health actions after the early warning system detects or produces a warning signal. We need to verify the reliability and validity of the warning signal, to conduct a risk assessment to see how it may affect public health, and to advise what kind of actions are required to prevent and control a communicable disease.

Objective To explore the epidemiology and etiology for an outbreak of acute respiratory tract infection that occurred in one county of Jiangsu Province, China 2004. Methods Only cases meeting the case definition were included in the study. We reviewed the medical records of the cases who were admitted to the local hospitals, interviewed cases by a standard questionnaire, and then described the epidemiologic features and analyzed risk factors by means of a case-control study. We collected pharyngeal swab specimens and sent them to different laboratories for isolation and culture. The laboratory used different detection methods such as DIF, PCR, electron microscope examination and microneutralization assay, to identify and then type the positive specimens. Results A total of 871 cases were reported during the period from April 18 to July 4, 2004. The distribution of onset times presented two peaks, one in late May and another in middle June. The epidemic occurred mainly in the elementary and junior high schools in ten townships of one county, and the mean age of the cases was 12 years (range 7 months to 18 years). The course of the disease was acute, and was characterized by fever accompanied with sore throat and tonsillitis. The WBC count of cases was normal or elevated. The mean duration of illness was 5 days (range 2 to 12 days). No fatalities from illness were reported. A case-control study indicated that the possible risk factors were close contact with a case and/or poultry before onset and sharing of towels among members of the family. The typical CPE was observed through inoculating pharyngeal swab specimens into the HEP-2 cell cultures in different laboratories. An infection of adenovirus type 3 was verified by detecting positive specimens in different methods. Conclusion This investigation demonstrated that the acute respiratory infection in cases was caused by adenovirus type 3. Cases occurred in over 70 schools in ten townships in 2004, and the route of transmission was possibly close contact with cases or droplet transmission.

To analyze the epidemiological characteristics of Middle East Respiratory Syndrome (MERS) outbreak in the Republic of Korea in 2015 and provide related information for the public health professionals in China.The incidence data of MERS were collected from the websites of the Korean government, WHO and authoritative media in Korea for this epidemiological analysis.Between May 20 and July 13, 2015, a total of 186 confirmed MERS cases (1 index case, 29 secondary cases, 125 third generation cases, 25 fourth generation cases and 6 cases without clear generation data), including 36 deaths (case fatality rate: 19%), were reported in Korea. All cases were associated with nosocomial transmission except the index case and two possible family infections. Sixteen hospitals in 11 districts in 5 provinces/municipalities in Korea reported confirmed MERS cases, involving 39 medical professionals or staff. For the confirmed cases and death cases, the median ages were 55 years and 70 years respectively, and the cases and deaths in males accounted for 60% and 67% respectively. Up to 78% of the deaths were with underlying medical conditions. Besides the index case, other 12 patients were reported to cause secondary cases, in which 1 caused 84 infections. One imported MERS case from Korea was confirmed in China on May 29, no secondary cases occurred. The viruses strains isolated from the cases in Korea and the imported case in China show no significant variation compared with the strains isolated in the Middle East.The epidemiological pattern of the MERS outbreak in Korea was similar to MERS outbreaks occurred in the Middle East.

To establish a comprehensive evaluation index system for the China Public Health Emergency Events Surveillance System (CPHEESS).A draft index system was built through literature review and under the consideration of the characteristics on CPHEESS. Delphi method was adapted to determine the final index system.The index system was divided into primary, secondary and tertiary levels. There were 4 primary indicators: System structure, Network platform, Surveillance implementation reports with Data analysis and utilization. There were 16 secondary and 70 tertiary indicators being set, with System structure including 14 tertiary indicators (accounted for 20.00%), 21 Network platforms (accounted for 30.00%). Twenty-four Surveillance implementation reports (accounted for 34.29%), 11 Data analysis and utilization (accounted for 15.71%). The average score of importance of each indicators was 4.29 (3.77-4.94), with an average coefficient variation as 0.14 (0.12-0.16). The mean Chronbach's α index was 0.84 (0.81-0.89). The adaptability of each related facilities indicator was specified.The primary indicators were set in accordance with the characteristics and goals of the surveillance systems. Secondary indicators provided key elements in the management and control of the system while the tertiary indicators were available and operative. The agreement rate of experts was high with good validity and reliability. This index system could be used for CPHEESS in future.

To analyze the information obtained through Internet-based media surveillance in 2013 on domestic public health emergencies and to compare with the related data reported through Chinese Public Health Emergency Management Information System (PHEMIS), and to study the role of Internet-based Media Surveillance Program (IBMSP) in the detection of public health emergencies.A descriptive analysis was conducted based on the database of the information on domestic public health emergencies. Information was obtained through the Internet-based media surveillance in 2013.A total of 752 pieces of information regarding domestic public health emergencies in 31 provinces were obtained, through the IBMSP, run by the China CDC in 2013. 53.46% of all the information were categorized as initial ones on public health emergency while another 22.07% were considered as updated ones. 41.62% of the information were related to infectious diseases with another 24.73% to food poisoning. 27.53% of the information were from official websites of governments and professional organizations, with the rest 72.47% were from media. As for corresponding public health emergencies, 41.79% were food poisoning and 18.66% were infectious diseases. 22.39% of them occurred in schools, 18.16% in other organizations and 16.92% in households. 28.86% were reported through Chinese PHEMIS. For the 116 public health emergencies that both related to information obtained through Internet-based media surveillance in 2013 and reported through PHEMIS, the median days of interval between illness onset of the first case as well as reported by media, interval between onset of the first case as well as reported through PHEMIS, were 2.5 days and 2.0 days respectively. 19.83% of the emergencies were first reported by media than through PHEMIS.Internet-based media surveillance programs had become an important way to detect public health emergencies and could serve as the supplement to the classic surveillance programs on public health emergencies.

To investigate the epidemiological characteristics of human infections with avian influenza A (H7N9) in China and to provide scientific evidence for the adjustment of preventive strategy and control measures.Demographic and epidemiologic information on human cases were collected from both reported data of field epidemiological investigation and the reporting system for infectious diseases.A total of 433 cases including 163 deaths were reported in mainland China before June 4, 2014. Two obvious epidemic peaks were noticed, in March to April, 2013 and January to February, 2014. Confirmed cases emerged in 14 areas of China. Five provinces, including Zhejiang, Guangdong, Jiangsu, Shanghai, and Hunan, reported about 85% of the total cases. Median age of the confirmed cases was 58 years (range, 1-91), with 70% as males. Of the 418 cases with available data, 87% had ever exposed to live poultry or contaminated environments. 14 clusters were identified but human to human transmission could not be ruled out in 9 clusters.Human infections with avian influenza A (H7N9) virus showed the characteristics of obvious seasonal distribution, with certain regional clusters. The majority of confirmed cases were among the elderly, with more males seen than the females. Data showed that main source of infection was live poultry and the live poultry market had played a significant role in the transmission of the virus.

We recently determined that Nanjianyin virus, isolated from serum of a patient in Yunnan Province, China, in 1989, is a type of Kyasanur Forest disease virus. Results of a 1987-1990 seroepidemiologic investigation in Yunnan Province had shown that residents of the Hengduan Mountain region had been infected with Nanjianyin virus.

To understand the Escherichia coli O157:H7 carrier rate of host animals and the toxic gene of the strains in different areas in Jiangsu province.Surveillance spots were set up in different areas, to collect feces of pigs, chickens, sheep, cattle to culture for O157:H7 with immunomagnetic separation as well as detection of toxic gene of the strain with MPCR were both carried out.One hundred and seventy strains of O157:H7 were separated from 1 767 feces of different animals in six spots, with a overall positive rate 9.62%. The positive rates of cattle and sheep were 19.05% and 12.01% respectively. Among 85 strains SLT1, SLT2, eaeA and hly toxic genes were detected. In which, 56.47% of the strains were positive curturely while 79.17% of them carried SLT2, eaeA and hly gene simultaneously.The positive rate of O157:H7 in animals and the positive rates of strains were correlated to the incidence of the area. The highest rates were seen in areas where there had been O157:H7 epidemic, followed by the areas where there were only scattered cases identified while the lowest was in areas with no patients. Data indicated that it was important to enforce the surveillance of O157:H7 in animals to better predict and control of the disease.

Human granulocytic anaplasmosis (HGA) is an emerging tick-borne disease in China. A cluster of cases among health care workers and family members following exposure to a patient with fulminant disease consistent with HGA prompted investigation.To investigate the origin and transmission of apparent nosocomial cases of febrile illness in the Anhui Province.After exposure to an index patient whose fatal illness was characterized by fever and hemorrhage at a primary care hospital and regional tertiary care hospital's isolation ward, secondary cases with febrile illness who were suspected of being exposed were tested for antibodies against Anaplasma phagocytophilum and by polymerase chain reaction (PCR) and DNA sequencing for A. phagocytophilum DNA. Potential sources of exposure were investigated.Cases with serological or PCR evidence of HGA were compared with uninfected contacts to define the attack rate, relative risk of illness, and potential risks for exposure during the provision of care to the index patient.In a regional hospital of Anhui Province, China, between November 9 and 17, 2006, a cluster of 9 febrile patients with leukopenia, thrombocytopenia, and elevated serum aminotransferase levels were diagnosed with HGA by PCR for A. phagocytophilum DNA in peripheral blood and by seroconversion to A. phagocytophilum. No patients had tick bites. All 9 patients had contact with the index patient within 12 hours of her death from suspected fatal HGA while she experienced extensive hemorrhage and underwent endotracheal intubation. The attack rate was 32.1% vs 0% (P = .04) among contacts exposed at 50 cm or closer, 45% vs 0% (P = .001) among those exposed for more than 2 hours, 75% vs 0% (P.001) among those reporting contact with blood secretions, and 87.5% vs 0% (P = .004) among those reporting contact with respiratory secretions from the index patient.We report the identification of HGA in China and likely nosocomial transmission of HGA from direct contact with blood or respiratory secretions.

Objective: To report a training course on the laboratory diagnoses of rickettsioses that 10 provincial/city CDCs participated in laboratory external quality assurance (EQA) based on the serological specific antibodies detection and rapid PCR amplifying targeted genes of rickettsiae. Methods: An EQA program to evaluate the following laboratory procedures was developed to detect rickettsiae: (1) immunofluorescent assay (IFA) to detect specific antibodies of A. phagocytophilum, R. heilongjiangensis and O. tsutsugamshi respectively. (2) Two sets of nested PCR were used amplifying groEL genes for most members of the family Rickettsiaceae and amplifying 16SrRNA genes for the most members of family anaplasmae, respectively. A scoring scheme based on the distribution of the median antibody titer values of the serologic assays was designed and a ranking list of the scores of the PCR results based on the detected minimal copy numbers of reference DNA was created. Results: Among nine laboratories who reported the results on time, eight laboratories gave acceptable serologic results, the other one provided an unacceptable antibody titer (1:2 vs median 1:64) results for O. tsutsugamshi. The limits of detection (LOD) for the PCR amplifying for five references DNA ranged from lcopy/μL to 10^6 copy/μL. Conclusions: We successfully trained and popularized modern diagnostic methods of rickettsiae in 10 provincial CDCs in China and first conducted the EQA projects and evaluated the results.

Screening admission diagnoses list. (DOCX 45 kb)

Screening admission diagnoses list. (DOCX 45 kb)

Background H7N9 human cases were first detected in mainland China in March 2013. Circulation of this virus has continued each year shifting to typical winter months. We compared the clinical and epidemiologic characteristics for the first three waves of virus circulation. Methods The first wave was defined as reported cases with onset dates between March 31-September 30, 2013, the second wave was defined as October 1, 2013-September 30, 2014 and the third wave was defined as October 1, 2014-September 30, 2015. We used simple descriptive statistics to compare characteristics of the three distinct waves of virus circulation. Results In mainland China, 134 cases, 306 cases and 219 cases were detected and reported in first three waves, respectively. The median age of cases was statistically significantly older in the first wave (61 years vs. 56 years, 56 years, p