In order to respond to severe changes in the situation surrounding infectious diseases, the Infectious Diseases Act (formal name: Law Concerning Prevention of Infectious Diseases and Medical Care for Patients with Infectious Diseases) was implemented from April 1, 1999 instead of the Infectious Diseases Prevention Act so far, and measures to prevent infectious diseases and measures to harmonize the patient’s human rights have been taken.
The Infectious Diseases Act was revised on October 16, 2003 (enforced on November 5, 2003) and also revised from April 1, 2007, and integrated with the Tuberculosis Prevention Act in order to respond to changes in the environments surrounding health and medical care, as people and supplies move rapidly and actively as infectious diseases occur abroad, such as SARS (Severe Acute Respiratory Syndrome), which has spread worldwide between November and early July 2002.
In preparation for the spread of highly pathogenic avian influenza (H5N1) and the outbreak of pandemic influenza, it was revised on May 2, 2008 (enforced on May 12).
The Infectious Diseases Act classifies infectious diseases First to fifth classes, five categories, designated infectious diseases, and seven categories based on the severity of symptoms and the infectivity of pathogens. In addition, the revision in May 2008 resulted in the addition of “Infectious Diseases such as Pandemic Influenza.” Different types of infectious diseases can be handled by different medical institutions, enabling countermeasures to be taken in accordance with each risk level.
Drug-resistant Acinetobacter infections caused by nosocomial infections have been added to class 5 infections, and chikungunya fever, a mosquito medium, has been added to class 4 infections.
The Middle East Respiratory Syndrome (MERS), where cases of infection have persisted mainly in the Middle East since 2012, and avian influenza H7N9, which has been confirmed to be transmitted to humans since 2013, were designated as two infectious diseases equivalent to avian influenza A (H5N1), considering their pathogenicity and infectivity.
In response to changing infectious diseases, the law system has been established and measures have been improved.

[Classification of Infectious Diseases in Infectious Diseases Act].

Classification Definition Infections name
1 class infection Highly dangerous infectious diseases
From a comprehensive perspective based on infectivity and seriousness of the disease
Ebola hemorrhagic fever;
Hemorrhagic fever; Smallpox;
South American hemorrhagic
Fever; Plague; Marburg isease;
Lassa fever
2 class infection High-risk infections from a comprehensive
perspective based on nfectivity and seriousness of the disease
Acute poliomyelitis, tuberculosis, diphtheria, severe acute respiratory syndrome}
(limited to those in Which the pathogen is a coronavirus genus SARS coronavirus), Middle East respiratory syndrome
(limited to those in which the pathogen is a betacoronavirus genus MERS
3 class infection Infectious diseases that can ause outbreaks of I nfectious diseases by employment in specific occupations, although the risk is not high from a comprehensive perspective based on infectivity, seriousness of the disease, etc. Cholera;
enterohemorrhagic E. coli infection;
4 class infection There are few human-to-human Infections, but infectious diseases that can infect humans through objects such as animals, foods, and drinks and may affect the health of the public. Hepatitis E, West Nile fever (including West Nile encephalitis), Hepatitis A, Echinococcosis, Yellow fever, Omsk hemorrhagic fever, Relapsing fever, Casanur Forest disease, Q fever, Rabies, Coccidioidomycosis, Monkeypox, Zika virus infection, Severe Febrile Thrombocytopenia Syndrome (only if the pathogen is Phlebovirus SFTS virus.), nephrotic symptomatic hemorrhagic fever, Western equine encephalitis, anthrax, chikungunya fever, Typhus disease, dengue fever, eastern Equine encephalitis, avian influenza (excluding avian influenza (H5N1 and H7N9H5N1)), Nipah virus infection, Japanese encephalitis, hantavirus pulmonary syndrome, B virus disease, meliosis, Venezuelan equine encephalitis, hendra virus infection, episodes, botulinum,  tularemia, Lyme disease, Rift Valley fever, Melioidosis, leptospirosis
5 class infection Infectious diseases that should be prevented from occurring and spreading by conducting surveys on the trends of infectious diseases in Japan and providing and Disseminating necessary information to the public and healthcare professionals based on the outcomes Amebic dysentery, viral hepatitis (excluding hepatitis E and hepatitis A), carbapenem-resistant Enterobacte riaceaebacterial infections, acute encephalitis(West Nile encephalitis, tick-borneencephalitis, eastern equine encephalitis, Japanese encephalitis, Venezuelan equine encephalitis and Rift Valley fever), cryptosporidiosis, Creutzfeldt-Jakob disease, fulminant hemolytic Streptococcal infection, acquired immunodeficiency syndrome, Giardia infection, invasive meningococcal infection, invasive pneumococcal infection, chickenpox (limited to hospitalized cases), congenital rubella syndrome syphilis, disseminated cryptococcosis, tetanus, vancomycin-resistant Staphylococcus aureus infection, pertussis, rubella, measles, drug-resistant Acinetobacter infection, respiratory syncytial virus infection, pharyngococcal fever, group A haemolytic gastroenteritis, varicella, hand-foot-mouth disease, Erythema contagiosum, herpangina, mumps, Influenza (excluding infections such as avian influenza and pandemic influenza), acute hemorrhagic Conjunctivitis, epidemic keratoconjunctivitis, genital Chlamydial infection, genital herpesvirus infection, condyloma acuminatum, gonococcal infection, chlamydial pneumonia (excluding psittacosis), bacterial meningitis (excluding invasive Haemophilus influenzae infection, invasive meningococcal infection, and invasive pneumococcal infection), mycoplasma pneumonia, aseptic meningitis, penicillin-resistant pneumococcal infection, methicillin-resistant Staphylococcus aureus infection, and drug-resistant Pseudomonas aeruginosa infection
New influenza and other infectious diseases Pandemic Influenza: Influenza caused by a virus that has the capacity to spread from person to person. Influenza is an influenza that is recognized as having a serious impact on the life and health of people due to the rapid spread of the infectious disease nationwide since the public has not generally acquired immunity to the infectious disease.
Re-emerging influenza: Re-emerging influenza is influenza that has once infection worldwide for a long time without epidemic, and is Recognized as having a serious impact on the life and health of the population due to the rapid spread of the infectious disease nationwide,  since most of the current population has not acquired immunity to the infectious disease.
Designated infectious disease Infectious diseases not classified as Category 1 to 3 or Pandemic Influenza InfectiousDiseases, for which measures according to Category 1 to Category 3 need to be taken  (designated by the government ordinance, limited to 1 year)
New infectious disease Infectious diseases that are

found to be transmittedfrom person to person, which are distinctly different from known I Nfectious diseases in terms  of symptoms and transmission power and Severity of the disease, and which have a very high  risk as determined by the seriousness of the infection

The prefectural governors provide Individual first aid with technical guidance and advice from the Ministry of Health, Labour and Welfare.[After designation of government ordinance]
Respond according to a class I infectious disease after complying with the requirements of symptoms, etc. according to a government  ordinance.

(Revised: November 21, 2014; enforced: April 1, 2016).