国立感染症研究所

国立感染症研究所では、当研究所で分離されたCOVID-19の原因ウイルス(SARS-CoV-2)の分与について、まだ、他施設では入手が困難であったことから本業務を優先的に実施してきました。しかしながら、すでに国内外の試験研究機関等約100カ所に分与していることから、本業務を優先的に実施することを2020年6月30日をもって終了致します。尚、以後、本件に関する個別の相談先は病原体担当部(ウイルス第三部、メール:This email address is being protected from spambots. You need JavaScript enabled to view it. )となります。

過去記事「新型コロナウイルスの分与について」

<Rapid report>Outbreak of novel coronavirus disease (COVID-19) on a cruise ship docked in Nagasaki City: preliminary interim report

Posted date 2020/6/3

In this report, we describe an outbreak of novel coronavirus disease (COVID-19) that occurred on the cruise ship, “Costa Atlantica”, docked in Nagasaki City, Nagasaki Prefecture. This report provides information pertaining to the confirmation of a cluster of COVID-19 cases, the initial test results, and the early situation on the ship. Response activities are currently ongoing, and this report should be considered as preliminary and interim.

On 29 January 2020, the Italian cruise ship, “Costa Atlantica”, entered Nagasaki Port and docked inside the port on 20 February, remaining there until 25 March for ship repairs. Since then, given the enhanced quarantine measures implemented globally, departure became difficult and the ship continued to remain in Nagasaki Port. All persons on the ship were crew members, with 623 persons on board on 20 April 2020. Many were young male adults; 523 (84%) were men with a median age of 31 years (range: 19-69 years). The majority were of foreign nationality, with the Philippines, India, Indonesia, and China (listed in descending order) contributing the largest number of crew members.

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 (https://www.niid.go.jp/niid/en/2019-ncov-e/2484-idsc/9497-covid19-14-200309-e.html), 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.

Descriptive epidemiology of 287 confirmed cases of new coronavirus infection reported by the national epidemiological surveillance of infectious disease system (NESID) and active epidemiological surveillance (as of March 9, 2020)

Posted date 2020/3/17

On February 1, 2020, new coronavirus infectious disease (COVID-19) was added as a designated infectious disease under the Infectious Diseases Control Law, article 6 in paragraph 8, which required doctors to immediately report diagnosed COVID-19 cases to the public health center in their jurisdiction. These reported cases were aggregated through the national epidemiological surveillance of infectious diseases (NESID) system. Additionally, active epidemiological investigation could then 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 reported through NESID and active epidemiological investigations, as of March 9. Data in NESID were 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). This updated report provides additions to the report published on February 24 (https://www.niid.go.jp/niid/en/2019-ncov-e/2484-idsc/9473-2019-ncov-08-e-2.html). 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 have been delayed reporting or case notification not yet 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.

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.

IASR-logo

Case of First Human-to-Human Infection of Novel Coronavirus in Japan

(Date of posting bulletin: February 26, 2020)

The novel coronavirus (hereinafter, SARS-CoV-2) is a new type of coronavirus that has been detected in patients with pneumonia of unknown cause, which has occurred in Wuhan City, Hubei Province in the People's Republic of China since December 2019. On February 11, the World Health Organization (WHO) specified the official name for the novel coronavirus infection as “COVID-19 (coronavirus disease 2019)” (hereinafter referred to as “COVID-19”). This paper summarizes and reports the results of an active epidemiological surveillance forcases of human-to-human infection of COVID-19 in 3 persons with no travel history to Wuhan for 2 weeks before the onset of the disease, in cooperation with local governments.

Field Briefing: Diamond Princess COVID-19 Cases, 20 Feb Update

Background:

Please refer to Field Brief: Diamond Princess COVID-19 Cases (https://www.niid.go.jp/niid/en/2019-ncov-e/9407-covid-dp-fe-01.html).

Quarantine Measures:

The initial quarantine period for those onboard the Diamond Princess was 5-19 February, with passengers informed that the 14-day quarantine could be extended if they were exposed to additional risk, for example close contact with a confirmed COVID-19 case. Additional details on quarantine measures can be found in “Field Briefing: Diamond Princess COVID-19”.

Disembarkation Procedures:

Criteria for disembarkation of non-cases from the Diamond Princess included 1) completion of a 14-day period without sharing a cabin with a confirmed case; 2) a negative result for a SARS-CoV-2 by PCR in the final days of the period; and 3) no relevant symptoms identified during a medical screening in the final day of the period. As of 20 February, over 1600 individuals have been disembarked from the Diamond Princess. Initially, testing focused on high-risk persons. Beginning on 11 Feb, efforts shifted toward testing all passengers by PCR for SARS-CoV-2. Due to the number of persons on board, these efforts began with passengers over 80, then over 75, then over 70, etc. After all passengers had been tested, the focus shifted to testing all crew members. Although no international guidelines require PCR testing to clear a quarantine for COVID-19 outbreaks, the Japanese government sought to do so as an additional measure of assurance.

Data Collection:

In addition the data collection methods described in Field Brief: Diamond Princess COVID-19 Cases; retrospective data collection has also begun by gathering information from the ship’s onboard clinic. Data here have been analysed descriptively.

Preliminary Results:

As of 20 February, 619 cases have been confirmed (16.7 % of the population on board), including 82 crew and 537 passengers. A total 3011 respiratory specimens were tested, and 621 were positive (20.6%), including double tests. Persons aboard between 70 and 89 were the most affected (Table 1). Among confirmed COVID-19 cases with recorded symptom onset (n=197), there were 34 (17.3 %) with onset dates before 6 February, which was the first full day of quarantine, and 163 (82.7%) with onset dates on or after the 6th (Figure 1). Among these 197 cases, 163 occurred during the quarantine period (48 crew, 115 passengers), with 52–92 among passengers in cabins without a previously confirmed case (Table 2). Of these, 3–7 occurred after the median quarantine day (day 7). The proportion of COVID-19 cases confirmed among passengers increased with cabin occupancy (Figure 2). A total 318 (51%) of all confirmed cases were asymptomatic when the respiratory specimen was collected (10 crew and 308 passengers).

Preliminary Conclusions:

Based on current available epidemiologic information, there is clear evidence that substantial transmission of SARS-CoV-2 was occurring prior to arrival of Diamond Princess in Yokohama. The subsequent decline in the number of confirmed cases with reported onset dates, may be explained by the natural course of the outbreak, by the implementation of quarantine measures, or by other unknown factors. Based on the cabin occupancy findings and the number of cases identified in cabins with previously confirmed cases, passengers within cabins may have been exposed to a common source or may have transmitted the virus within cabins. Due to the nature of the ship, individual isolation of all those aboard was not possible. Sharing cabins was necessary, and some crew had to perform essential duties while passengers remained aboard. After accounting for delayed reporting, the peak number of confirmed cases with known onset dates occurred on 7 February. The high number of recently reported cases can be explained by the shift in testing strategy described above, most of which were asymptomatic.

The proportion of asymptomatic cases observed aboard Diamond Princess is substantially higher than what has been reported elsewhere. A major factor in this proportion is the systematic testing of passengers that began on 11 Feb and increased each day. Due to the lack of symptom presentation, it is not possible to infer when these cases were infected (see Annex A). Some may have been secondary cases within a given cabin. Some may have been infected before the quarantine began. Nevertheless, these asymptomatic cases were detected through testing, disembarked, and transferred to isolation. Their cabin mates have been defined as close contacts with their 14-day isolation reset on the last day the asymptomatic case disembarked. The systematic testing of asymptomatic cases was therefore important and beneficial for identifying potentially infectious individuals before allowing them to disembark. Current global research has scant evidence on asymptomatic transmission of SARS-CoV-2; thus, ongoing efforts to thoroughly investigate asymptomatic cases from Diamond Princess will provide important information for the global COVID-19 outbreak. (Information on the development of symptoms after disembarkation of asymptomatic confirmed cases is being collected.)

Surveillance staff are working on merging the data from Diamond Princess with information from reported COVID-19 cases in the National Epidemiological Surveillance of Infectious Diseases (NESID) to understand more about the clinical presentation, severity and initial asymptomatic presentation. This information will be important for further the understanding this event and the global situation of COVID-19.

Preliminary Actions/Guidance:

Nearly all disembarked individuals have observed a 14-day quarantine without sharing a cabin with a confirmed case, have received a recent negative PCR-test, and have passed a medical screening for symptoms (e.g. fever, cough,). Individuals who shared a cabin with a confirmed case will be put in isolation until they complete a 14-day beginning after the last day of contact with a confirmed COVID-19 cabinmate. This includes a large proportion of the crew, who admirably performed essential tasks that allowed the quarantine to occur and should be appreciated for their service. As more than 1600 individuals, primarily passengers, have been disembarked from Diamond Princess, the focus and support will now shift toward preventing further transmission of SARS-CoV-2 among crew.

Although the disembarked persons have passed laboratory testing, medical screening and the 14-day quarantine, they are asked to stay at home, where feasible, 14 days unless absolutely necessary, as an additional precautionary measure. They are asked also to monitor themselves for symptoms and contact a a healthcare facility if symptoms develop.

Note: this work would not have been possible without the important efforts of medical teams who went aboard Diamond Princess to care for passengers and crew and obtain this necessary information; the efforts of the crew to provide essential services; and the collaboration of Princess Cruises. 

 

Table 1. Percent of persons aboard confirmed with COVID-19 by age group and symptom status at the time of specimen collection. (As of 20 February).

Age group

Symptomatic confirmed cases (%)

Asymptomatic confirmed cases (%)

Total confirmed cases (%)

Persons aboard on 5 February 

00-09

0(0)

1(6)

1(6)

16

10-19

2(9)

3(13)

5(22)

23

20-29

25(7)

3(1)

28(8)

347

30-39

27(6)

7(2)

34(8)

428

40-49

19(6)

8(2)

27(8)

334

50-59

28(7)

31(8)

59(15)

398

60-69

76(8)

101(11)

177(19)

923

70-79

95(9)

139(14)

234(23)

1015

80-89

27(13)

25(12)

52(24)

216

90-99

2(18)

0(0)

2(18)

11

Total

301(8)

318(9)

619(17)

3711

 

Figure 1. Number of confirmed COVID-19 cases* with reported onset dates, by onset date, aboard Diamond Princess, 6 – 20 February 2020 (n=163)

  COVID DP2 Fig1 

 * The number of cases (n = 163) was based on the cases with available onset date reported.

 

Figure 2. Comparison of proportions of confirmed cases among passengers by cabin occupancy.

COVID DP2 Fig2 

 

Table 2. Characteristics of COVID-19 Cases with reported on-set dates of 6 – 17 Feb 2020 (n=163).

 

Day of Quarantine

Date of Onset

(n cases)

Crew

Passengers

Total

In cabins with a confirmed case

In cabins without a confirmed case

12

17 Feb (1)

1

0

0

0

11

16 Feb (2)

2

0

0

0

10

15 Feb (4)

3

1

0 [1]

0-1

9

14 Feb (7)

5

2

1 [0]

1

8

13 Feb (17)

8

9

4 [3]

2-5

7

12 Feb (12)

7

5

0 [2]

3-5

6

11 Feb (19)

8

11

3 [1]

7-8

5

10 Feb (10)

3

7

3 [1]

3-4

4

9 Feb (24)

5

19

6 [9]

4-13

3

8 Feb (19)

2

17

1 [7]

9-16

2

7 Feb (31)

2

29

4 [10]

15-25

1

6 Feb (17)

2

15

1 [6]

9-14

Total

48

115

23 [40]

52-92

The number in brackets represents the number of additional confirmed cases in the same cabin with unknown onset date. Due to the uncertainty of knowing which case came first, the column to the far right presents a range.

 

 

Annex A. Theoretical depiction of the identification of asymptomatic cases during the quarantine period.

COVID DP2 AnnexA 

Appreciation and Request from National Institute of Infectious Diseases, Japan

 
Dear Passenger,

We would like to extend our sincere gratitude for your patience and compliance in participating in the health observation period onboard the Diamond Princess from February 5th to 19th.

We would like to reassure you, based on your negative test results for the novel coronavirus and a successful medical visit confirming that you do not the fever or respiratory symptoms associated with the disease, that it is highly unlikely that you have been infected with the new coronavirus and can return to your normal lifestyle. We recognize that there may be concern for your health from many family and friends, so we would like to offer you the following guidance and requests from the National Institute of Infectious Diseases:

If you feel unwell during the next two weeks, please reach out for a consultation with the two institutes listed below:

  • A visitor hotline operated by the Japan National Tourism Organization (JNTO)
*Phone number: 050-3816-2787
http://www.mlit.go.jp/kankocho/content/001327108.pdf
(Support is available in English, Chinese and Korean)
  • 日本語でのコミュニケーションが可能な方については、以下へのご相談が可能です。
★各都道府県の新型コロナウイルスに関する帰国者・接触者相談センター★
(令和2年2月13日時点版)
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/covid19-kikokusyasessyokusya.html

In addition, as you have been carefully monitoring your health for the last two weeks, we would like to encourage you to continue with your usual disease prevention methods. This includes washing your hands often and wearing a mask.

We recognize that the recently disembarked passengers have been in the frontlines in the fight to prevent the invasion of emerging infectious diseases into Japan. We would like to request Japanese citizens for their maximum support in helping disembarked passengers regain their health and normal lifestyles. 

February 21, 2020

National Institute of Infectious Diseases, Japan

 


 

Field Briefing: Diamond Princess COVID-19 Cases

Background:

A cruise ship, named the Diamond Princess, had travel that originated in Yokohama on 20 January and included stops in Japan (Kagoshima), Hong Kong, Vietnam, Taiwan and Japan (Okinawa), before arriving back in Yokohama on 3 February. During this time, a passenger who disembarked on 25 January in Hong Kong, has presented with cough since 19 23 Jan and was confirmed positive for Novel coronavirus on 1 February. The Japanese government requested that the Diamond Princess stay at port, with no passengers or crew disembarking, in Yokohama when it arrived on 3 February. During 3-4 February, health status of all passengers and crew members were checked by questionnaire by quarantine officers, and respiratory specimens were taken from symptomatic passengers, crew, and their close contacts to test for Novel coronavirus. On 5 February, a lab-confirmed case of COVID-19 led to the quarantine of the Diamond Princess for 14 days beginning at 7am, with passengers requested to stay in their cabins. As of 5 February, there was a total of 3711 individuals on board the Diamond Princess, with 2666 passengers and 1045 crew members.

Quarantine Measures:

At the beginning of the quarantine period, crew members were provided with personal protective equipment (PPE) and instructed on appropriate IPC practices. On 7 February, passengers were provided thermometers for self-monitoring of body temperature, with instructions on calling a “Fever Call Center”, if they had a fever above 37.5C. Passengers who developed fever were referred to the medical team in charge and were tested for Novel coronavirus. Passengers who developed serious illness, including non-COVID-19 morbidities, were referred the ship’s Medical Center, which provided essential health services. Those passengers with lab-confirmed COVID-19 were disembarked and transferred to an isolation ward at healthcare facilities. Their cabinmates were defined as “close contacts” and were therefore tested. If positive, they were also confirmed as a case and disembarked to a healthcare facility. If they tested negative, they remained on board but with a 14-day quarantine period reset after the last contact with the confirmed case. All crew and healthcare staff onboard the Diamond Princess were instructed to follow international guidance on infection prevention and control. To maintain operations of the ship, some crew continued to perform essential, limited services while the ship remained in quarantine. This led to those crew members not remaining fully isolated, in the same manner as passengers, during the quarantine period.

Data Collection:

Initially, only symptomatic cases and close contacts were being tested for COVID-19. This was changed on 11 February, due to the expansion of laboratory capacity, with quarantine officers systematically collecting respiratory specimens from all passengers by age group, starting with those 80 years old and older as well as individuals with co-morbidities, such as diabetes or a heart condition. Respiratory specimens collected were tested via PCR for confirmation of Novel coronavirus. Epidemiological data collected was initially limited due to the emergency nature of the quarantine and included data on onset of symptoms, date of lab confirmation, and close contacts. A confirmed case of COVID-19, for this report, is anyone, passenger or crew, who had a positive PCR test for Novel coronavirus, independent of their symptom presentation. In most cases, the “population on board,” refers to the 3,711 passenger and crew aboard Diamond Princess on 5 February.

Preliminary Results:

As of 18 February, there have been 531 confirmed cases (14.3% of all individuals on board on 5 February), including 65 crew and 466 passengers. A total 2404 respiratory specimens were tested, and 542 were positive (22.5), including double tests. Among confirmed COVID-19 cases with recorded symptom onset (n=184), there were 33 (18%) with onset dates before 6 February, which was the first full day of quarantine, and 151 (82%) with onset dates on or after the 6th. A total 255 (48%) of the confirmed cases were asymptomatic when the respiratory specimen was collected. Of these, 8 were crew and 247 were passengers. (Information on development of symptoms after disembarkation of asymptomatic confirmed cases is not currently available.) A total 23 passengers with reported onset dates were confirmed after another passenger in the same cabin had been confirmed. From 13 February to now, 81% of cases among confirmed passengers or crew with reported onset dates (n=22) occurred in crew (n=13) or passengers from cabins with a previously confirmed case (n=5).

Preliminary Conclusions:

Based on the number of confirmed cases by onset date, there is clear evidence that substantial transmission of COVID-19 had been occurring prior to implementation of quarantine on the Diamond Princess on 5 February (see also febrile patient visits to the on-board clinic below). The decline in the number of confirmed cases, based on reported onset dates, implies that the quarantine intervention was effective in reducing transmission among passengers. Transmission toward the end of the quarantine period, which is scheduled to end for most passengers on 19 Feb, appears to have occurred mostly among crew or within passenger cabins. It should be noted that due to the nature of the ship, individual isolation of all those aboard was not possible. Sharing of cabins was necessary, and some crew had to continue to perform essential duties for the functioning of the vessel with passengers aboard.

Recent confirmations of asymptomatic cases can be explained by the systematic testing of passengers that began around 14 Feb. Although some of these cases may have been secondary cases within a given cabin, it is difficult to know when transmission occurred. They may have been infected before the quarantine began. Nevertheless, these asymptomatic cases have been disembarked and their cabinmates have been defined as close contacts with their 14-day isolation reset on the day the asymptomatic case was disembarked. The systematic testing of asymptomatic cases was useful in screening these persons before allowing them to disembark.

Preliminary Actions/Guidance:

Those persons (mostly passengers) who have completed the 14-day quarantine, have not tested positive, and pass a medical check on the 14th day, will be disembarked on the 19th.

Those individuals who were in contact with a confirmed case will be put in isolation until they complete the 14-day period beginning after the last day of their suspected contact with a case. This includes a large proportion of the crew members of the Diamond Princess. The crew performed essential tasks that allowed the quarantine to occur successfully for 14 days and should be appreciated for their service.

As the persons aboard were exposed to a high-risk environment for a prolonged period, all persons who disembark should be careful about the health conditions for the time being and immediately report to a public health center if they develop symptoms.

 

Percent of persons aboard who were confirmed with COVID-19 by age group and symptom status at the time of specimen collection.

Age group

Symptomatic confirmed cases (%)

Asymptomatic confirmed cases (%)

Total confirmed cases (%)

Persons aboard on 5 February 

00-09

0(0)

1(6)

1(6)

16

10-19

1(4)

1(4)

2(9)

23

20-29

18(5)

2(1)

20(6)

347

30-39

18(4)

5(1)

23(5)

429

40-49

18(5)

7(2)

25(8)

333

50-59

27(7)

22(6)

49(12)

398

60-69

73(8)

56(6)

129(14)

924

70-79

92(9)

136(13)

228(22)

1015

80-89

27(13)

25(12)

52(24)

215

90-99

2(18)

0(0)

2(18)

11

Total

276(7)

255(7)

531(14)

3711

 

Number of confirmed COVID-19 cases with reported onset dates, by onset date, aboard Diamond Princess, 6 – 17 February 2020 (n=151)

  COVID DP Fig1

 

Febrile Patients, by date of clinic visit, Diamond Princess clinic, 19 Jan - 2 Feb 2020 (n=79)

COVID DP Fig2 

 

Characteristics of COVID-19 Cases with reported on-set dates of 6 – 17 Feb 2020 (n=151)*.

Date of Onset (n cases)

Crew

Passengers

Passengers from cabins with another confirmed case (%)

17 Feb (0)

0

0

0

16 Feb (0)

0

0

0

15 Feb (1)

1

0

0

14 Feb (5)

4

1

1 (100%) [0]

13 Feb (16)

8

8

4 (50%) [2]

12 Feb (12)

7

5

0 (00%) [2]

11 Feb (18)

7

11

3 (27%) [1]

10 Feb (10)

3

7

3 (43%) [1]

9 Feb (24)

5

19

6 (32%) [9]

8 Feb (18)

2

16

1 (6%) [3]

7 Feb (31)

2

29

4 (14%) [10]

6 Feb (16)

1

15

1 (7%) [6]

Total

40

111

23 (21%) [34]

* The total number of cases in this table (n=151) is the total number of cases with known onset dates.
Note, the number in brackets represents the number of additional confirmed cases in the same cabin with unknown onset date.


Corrigendum:

  • The denominator in the table " Characteristics of COVID-19 Cases with reported on-set dates of 6 – 17 Feb 2020 (n=53)" was incorrect upon publication. This Briefing has been updated on 20 Feb to reflect the accurate number at time of publishing (n=151).

  • In Background, a passenger who disembarked on 25 January in Hong Kong has presented with cough since 19 Jan was incorrect upon publication. This parson has been coughed since 23 Jan.

Copyright 1998 National Institute of Infectious Diseases, Japan

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