Descriptive epidemiology of 112 confirmed cases of novel coronavirus infectious disease (COVID-19) as reported by the national epidemiological surveillance of infectious diseases (NESID) system and active epidemiological investigation (as of February 24, 2020)


On February 1, 2020, the novel coronavirus infectious disease (COVID-19) was added as a designated infectious disease under the Infectious Diseases Control Law, article 6 in paragraph 8, which requires doctors to immediately report diagnosed COVID-19 cases to the public health center in their jurisdiction. These reported cases are aggregated through the national epidemiological surveillance of infectious diseases (NESID) system. Additionally, active epidemiological investigation can be conducted, as stipulated in the Infectious Diseases Control Law, article 15.

The primary sources of data in this report were lab-confirmed COVID-19 cases notified through NESID and active epidemiological investigations, as of February 24. Data in NESID are aggregated from reporting by local public health centers. Daily data in active epidemiological investigation by local public health centers were aggregated by teams from the Novel Coronavirus Response Headquarters at the Ministry of Health, Labor, and Welfare (MHLW). As data collection is ongoing, this report may be revised or updated accordingly in the future. It should also be noted that there are cases in which there may be delayed reporting or case notification has not been completed. As such, there may be a difference in the number of cases reviewed in this report versus those under active investigation by MHLW. It is expected that this difference will be resolved in the future, but please note that there may be a difference.

Based on data reported as of February 24, 2020 by both NESID and MHLW’s active epidemiologic investigations, there were 112 lab-confirmed COVID-19 cases. The gender ratio was 1.6:1, with 69 males and 43 females in total. The median age was 66.5 (age range 15-89), with age distribution of 2 cases in the 10-19 range (2%), 7 cases in the 20-29 range (6%), 8 cases in the 30-39 range (7%), 9 cases in the 40-49 range (8%), 20 cases in the 50-59 range (18%), 13 cases in the 60-69 range (12%), 33 cases in the 70-79 range (29%), and 20 cases in the 80-89 range (18%). Approximately 60% of cases were identified in those over 60 years of age.

The nationality of cases were 75 cases from Japan, 11 from the United States, 7 from China, 7 from Australia, 4 from the Philippines, 3 from India, 3 from Canada, 1 from Thailand, and 1 from Hong Kong. The possible routes of infection identified were 72 cases originating from ship-based travel, 11 cases with travel history to China or Wuhan city, 11 cases in Tokyo, 11 cases in Wakayama, 2 cases in Chiba, 1 case in Kanagawa, 1 case in Osaka, 1 case in Ishikawa, 1 case with unknown Japanese prefecture, and 1 case with unknown infection transmission route.

Figure 1 shows the epidemic curve for the 90 cases with known dates of symptom onset, from January 20-February 19, 2020.  As shown, confirmed ship-related COVID-19 cases of crew and passengers peaked on February 7th and confirmed cases with links to China or Wuhan were higher in January, with the other cases having a sporadic spread over the timeframe.

At of case report day, the main symptoms identified were fever 81/112 (72%), cough 69/112 (62%), pneumonia 43/66 (65%), sore throat 23/68 (34 %), general malaise 20/61 (33%), nasal discharge or congestion 17/64 (27%), headache 17/62 (27%), diarrhea 11/64 (17%), nausea and/or vomiting 5/60 (8%), joint or muscle pain 4/58 (7%), acute respiratory distress syndrome (ARDS) 3/41 (7%), and conjunctival congestion 0/53 cases (0%). Please note that the change in denominators was due to the exclusion of a case from the total if there was no information provided for that symptom or if it was unknown.

In table 1, the number of reported cases by age group for each symptom is shown. At the time of COVID-19 case diagnosis, 21/112 cases (19%) were reported as asymptomatic cases. Out of the reported 21 asymptomatic cases, 5 cases had symptom onset dates provided which were either before the date of diagnosis or the same as the date of diagnosis. Of the remaining 16 reported asymptomatic cases, there were 4 symptomatic cases included without symptom onset dates provided and 6 symptomatic cases with symptom onset dates after the date of diagnosis. Excluding these 15 cases which were misclassified as asymptomatic, there were 6/112 asymptomatic cases (5%), as of February 24.

Table 1 also shows the medical interventions as reported by age group. Intensive care unit (ICU) admission was 8/52 (15%) and invasive ventilation (tracheal intubation) was 11/50 (22%). Other interventions used included extracorporeal membrane oxygenator (ECMO) in 5 patients, with 1 in their 40s, 1 in their 60s, 2 in their 70s, and 1 in their 80s. As of February 24, there were no deaths reported in the 112 cases analyzed. Please note that the change in denominators was due to the exclusion of a case from the total if there was no information provided for that medical intervention or if it was unknown.

Regarding severe cases requiring medical interventions, the presence of co-morbidities was analyzed. For the 8 cases requiring ICU admission: 4 cases had known co-morbidities, 1 case had no co-morbidities, and 3 cases had unknown status for co-morbidities. For the 11 cases requiring invasive ventilation: 5 cases had known co-morbidities, 1 case with no co-morbidities, 5 cases had unknown status for co-morbidities. For the 5 cases requiring ECMO: 3 cases had known co-morbidities and 2 cases had unknown status for co-morbidities.

This report summarizes a part of the PCR-positive cases in Japan (reported by the Ministry of Health, Labor and Welfare on February 25: 140 in domestic, 15 returnees on charter flights, and 691 crews and passengers in cruise ships). We will continue to collect, analyze, and feedback information on COVID-19 in Japan in order to understand the trends and the severity of the disease, and to reflect them in measures.

We would like to extend our sincere gratitude to the local government officials and public health centers for their continued cooperation in reporting COVID-19 cases during the outbreak as part of the NESID system. 


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Copyright 1998 National Institute of Infectious Diseases, Japan