Descriptive epidemiology of 516 confirmed cases of novel coronavirus infection reported by the national epidemiological surveillance of infectious diseases (NESID) system and active epidemiological surveillance (as of March 23, 2020)

Posted date 2020/4/9

On February 1, 2020, novel coronavirus infectious disease (COVID-19) was added as a designated infectious disease under the Infectious Diseases Control Law, article 6 in paragraph 8, requiring physicians to immediately report diagnosed novel coronavirus infection cases to the public health center in their jurisdiction. Additionally, active epidemiological investigation became possible, as stipulated in the Infectious Diseases Control Law, article 15.

The primary sources of data in this report were lab-confirmed novel coronavirus infection cases (including asymptomatic SARS-CoV-2 infection cases) reported through both the National Epidemiological Surveillance of Infectious Diseases (NESID) system and the active epidemiological investigation program, as of March 23. Cases reported by local public health centers through NESID were linked to cases monitored daily for follow-up by members of the Novel Coronavirus Response Headquarters team at the Ministry of Health, Labour and Welfare (MHLW), via the active epidemiological investigation program. This report provides an update to the previous report for the data as of March 9 (, and is the third update thus far. As data collection is ongoing, the data may be revised or updated accordingly in the future. It should also be noted that there is delayed reporting or cases still in the process of notification for some cases. As such, there may be a difference in the number of cases in this report versus those officially reported by MHLW. It is expected that this difference will be gradually resolved in the future, but caution is required.

Based on data reported as of March 23, 2020, 516 lab-confirmed novel coronavirus infection cases could be linked among the cases reported through both NESID and the MHLW’s active epidemiologic investigation program.

The gender ratio was 1.2:1, higher for males, with 285 males and 231 females.

The median age was 60 years (age range 1-97), with the following age distribution: 6 under 10 years (1.2%), 3 aged 10-19 years (0.6%), 46 aged 20-29 years (8.9%), 52 aged 30-39 years (10.1%), 59 aged 40-49 years (11.4%), 87 aged 50-59 years (16.9%), 98 aged 60-69 years (19.0%), 124 aged 70-79 years (24.0%), 39 aged 80-89 years (7.6%), and 2 aged 90 years or older (0.4%). Approximately 50% of cases were 60 years of age or older.

The nationality of cases were as follows: 405 from Japan, 25 from the United States, 20 from Australia, 13 from China, 9 from Canada, 9 from the Philippines, 7 from India, 5 from Indonesia, 5 from Hong Kong, 3 from Thailand, 2 from New Zealand, 2 from France, 1 from Ireland, 1 from Ukraine, 1 from Colombia, 1 from Hungary, 1 from Romania, 1 from Russia, 1 from South Africa, and 4 with unconfirmed nationality.

The suspected route of infection or location of infection were as follows: 214 cases associated with a cruise ship (crew and passengers), 65 in Osaka, 30 in Tokyo, 23 in Niigata, 19 in Kanagawa, 14 in Wakayama, 13 in Chiba, 10 in Gunma, 7 in Kyoto, 7 in Oita, 3 in Hokkaido, 3 in Aichi, 3 in Fukuoka, 2 in Saitama, 2 in Ishikawa, 2 in Gifu, 2 in Hyogo, 2 in Yamaguchi, 1 in Nagano, 1 in Hiroshima, 1 in Kumamoto, 1 in Miyazaki, and 15 cases with prefecture information unknown; among suspected imported cases, 11 were associated with China, 5 with Egypt, 3 with Italy, 3 with the United Kingdom, 3 with Spain, 3 with France, 2 with the Philippines, 1 with Ireland, 1 with Switzerland, 1 with Thailand, and 1 with the United States; among cases suspected as potentially domestic or imported, 1 was associated with Hokkaido/Hawaii, 1 with Ishikawa/Egypt, 1 with Ishikawa/France, 1 with Nagano/France, 1 with Fukuoka/South Korea, 1 with an unknown prefecture/Egypt, 1 with an unknown prefecture/the United States, 1 with Italy/the Netherlands, 1 with Spain/France, 1 with Russia/Finland, 1 with the United Kingdom/France/Italy, 1 with Spain/France/Belgium, 1 with an unknown prefecture/Singapore/Indonesia, and 29 with unknown location of infection.

The figure shows the epidemic curves of 405 cases with known dates of symptom onset, from January 20 to March 21, 2020. The confirmed cruise ship-related cases among passengers and crew peaked on February 7 and confirmed cases with travel history to China or Wuhan city were high in January, with domestic cases increasing gradually since mid-February.

The table shows the number of reported cases by age group for each sign/symptom and medical intervention. From the time when the case was reported until March 23, the main signs/symptoms identified were fever 375/475 (79%), cough 353/465 (76%), pneumonia 245/387 (63%), general malaise 182/389 (47%), sore throat 115/393 (29%), nasal discharge and/or nasal congestion 79/321 (25%), headache 71/301 (24%), diarrhea 65/336 (19%), joint and/or muscular pain 42/310 (14%), nausea and/or vomiting 20/318 (6%), acute respiratory distress syndrome (ARDS) 10/277 (4%), and conjunctival congestion 6/283 (2%). The denominator values vary as cases with information on signs/symptoms missing or unknown were excluded from the denominator.

For medical interventions used, there were 35/323 (11%) intensive care unit (ICU) admissions and 49/347 (14%) invasive ventilation (including endotracheal intubation). Other interventions used included extracorporeal membrane oxygenator (ECMO) in 18 cases, with 2 in their 40s, 5 in their 60s, 9 in their 70s, and 2 in their 80s. Denominator values vary as cases with information on medical intervention missing or unknown were excluded from the denominator; interpretation thus requires caution as the proportions may be overestimated.

Regarding severe cases requiring medical interventions, the presence of co-morbidities was analyzed. For the 35 cases requiring ICU admission, there were 17 with co-morbidities, 5 with no co-morbidities, and 13 with unknown status/no information for co-morbidities. For the 49 cases requiring invasive ventilation, there were 29 with co-morbidities, 4 with no co-morbidities, 16 with unknown status/no information for co-morbidities. For the 18 cases requiring ECMO, there were 11 with co-morbidities, 2 with no co-morbidities, and 5 with unknown status/no information for co-morbidities. The co-morbidities among the 49 cases requiring invasive ventilation included diabetes (13 persons), hypertension (12 persons), dyslipidemia (10 persons), cardiovascular disease (5 persons), and malignant neoplasms (5 persons). The co-morbidities among the 18 cases requiring ECMO included hypertension (5 persons), diabetes (4 persons), dyslipidemia (4 persons), and cardiovascular disease (4 persons). Multiple co-morbidities were identified in some cases.

At the time of novel coronavirus infection case notification, 91 cases (18%) were reported as asymptomatic. Among the reported 91 asymptomatic cases, based on subsequent active epidemiological investigations, 11 cases were found to be symptomatic before the notification, 11 subsequently developed symptoms (i.e. presymptomatic at the time of notification), and 29 also subsequently developed symptoms but the date of symptom onset was not recorded. Of the 91 patients reported as asymptomatic cases, 6 (7%) required invasive ventilation (including endotracheal intubation) and 3 (3%) required ECMO. As of March 23, 40 of the cases reported as asymptomatic remained asymptomatic (no symptoms reported), which was 8% of the total 516 cases and 44% of the cases reported as asymptomatic cases at the time of notification.

As of March 23, among the 516 cases analyzed, 10 had died (2%) and 261 had been discharged from hospital (51%). Among the 226 with known hospitalization and discharge dates, the mean length of hospitalization was 16.6 days (standard deviation ± 7.9). Underlying co-morbidities in the fatal cases included diabetes (4 persons), malignant neoplasm (3 persons), hypertension (2 persons), and cerebral and cardiovascular diseases (2 persons). Multiple co-morbidities were identified in some case.

This report summarized a portion of the overall lab-confirmed novel coronavirus infection cases in Japan, as reported by the MHLW on March 23: 1,057 domestically cases in Japan, 15 returnee cases from chartered flights, 17 cases detected at airport quarantine, and 712 cases associated with the cruise ship. We will continue to collect, analyze, and feedback information on novel coronavirus infection cases in Japan in order to understand the trends and the severity of the disease and to inform intervention measures.

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

【Figure】Confirmed COVID-19 cases by date of onset, Jan-20 to Mar-21, based on data from the National Epidemiological Surveillance of Infectious Diseases (NESID) system and active epidemiological investigations, as of Mar 23 (n=405)
*Given the time it takes from onset to report, care must be taken in interpretation as cases with recent onset may not yet be reported. A: cases among cruise ship passengers and crew members; B: other cases.
14 200323 e f1
14 200323 e t1


June 8, 2020   Figure. B (Unknown Domestic or International) have been corrected.

Copyright 1998 National Institute of Infectious Diseases, Japan