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Toppage > Surveillance > Pertussis, Epidemiological week 1-21, 2025 (as at 28 May 2025)

Pertussis, Epidemiological week 1-21, 2025 (as at 28 May 2025)

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◆Pertussis, Epidemiological week 1-21, 2025 (as at 28 May 2025)

Pertussis is an acute respiratory tract infection caused mainly by Bordetella pertussis, and the main routes of infection are droplet infection and contact infection. Although Bordetella parapertussis can also cause pertussis, only infections caused by B. pertussis should be notified under the Infectious Diseases Control Law in Japan. The illness progresses through three phases: catarrhal stage (cold-like symptoms), paroxysmal stage (paroxysmal coughs, whooping, etc.), and convalescent stage (gradual recovery), with recovery usually taking two to three months. In early infancy, the characteristic cough may not be observed. In some cases, apnea episodes can progress to respiratory arrest. Complications such as pneumonia and encephalopathy have also been reported, making it particularly important to pay special attention. In adults, the disease is often mild and may be overlooked, even if the cough persists for a long time. Pertussis is mainly treated with macrolide antibiotics. The cornerstone of prevention during childhood is the four-dose regimen of routine immunization with the 5-in-1 vaccine (DPT-IPV-Hib), in addition to basic hand hygiene and other infection control measures.

In Japan, pertussis has been a category V notifiable disease under the Infectious Diseases Control Law since 1 January 2018. It was a category V pediatric sentinel surveillance disease through 2017 but was reclassified as a notifiable disease, allowing for more accurate monitoring of its epidemiology and incidence trends nationwide. Pertussis is subject to notification when the patient has clinical features such as coughing and is diagnosed by one of the following methods: isolation and identification of the pathogen, amplification and detection of pathogen genes, antigen detection by immunochromatography, or antibody detection. It must also be reported in cases where, even without laboratory findings, the patient had contact with a confirmed case and the clinical features are consistent with pertussis (clinical diagnosis). In addition, the disease is designated as a Class II infectious disease under the School Health and Safety Act. The aim of this article is to provide the most recent information on the epidemiology of pertussis in Japan, mainly based on the National Epidemiological Surveillance of Infectious Diseases.

As at 28 May 2025, the cumulative number of reported pertussis cases diagnosed in the first 21 weeks of 2025 was 22,351, marking the highest number recorded for the same period since surveillance for the disease as a notifiable disease began in 2018. The annual number of reported cases in 2024 was 4,096, while the cumulative number reported through week 21 of 2025 has already exceeded five times the total number of cases reported last year. In addition, from 2018 to 2024, by week of diagnosis, there were no weeks during weeks 1-21 in which the number of cases reported exceeded 500. However, in 2025, 571 cases were reported in week 10. A particularly notable increase has been observed since week 15, with 1,611 cases reported that week, and then more than 2,000 cases reported each week from week 16 onward.

Of the 22,351 cases reported, 21,689 (97%) cases were diagnosed using some type of testing, of which nucleic acid amplification methods such as PCR or LAMP were performed in 13,501 (62%) cases. 662 (3%) were reported by clinical diagnosis. 11,366 cases were male, 10,983 cases were female, and 2 cases had unknown sex, with a median age of 12 years (range: 0-99 years). By age group, 10–19-year-olds accounted for 58.7% of the cumulative reported cases during weeks 1-21 of 2025, showing a marked increase compared to previous years' levels. In addition, the proportion of cases among those aged 20 years and above was lower than in previous years. The cumulative number (n) and percentage of case reports by age group for weeks 1-21 of 2018-2025 are shown in Table 1.

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The top three prefectures in terms of cumulative case reports in weeks 1-21 of 2025 were Niigata (1,473 cases), Tokyo (1,448 cases), and Osaka (1,276 cases), while the highest number of reported cases per 100,000 population was Miyazaki (81.1 cases), followed by Niigata (70.2 cases) and Kochi (68.9 cases). Regarding vaccination history, 581 cases had no vaccination history, 188 cases had one dose, 98 cases had two doses, 592 cases had three doses, 13,072 cases had four doses, and 7,820 cases had unknown vaccination history.

The cumulative number of reported pertussis cases diagnosed in weeks 1-21 in each year of 2018-2025, the number of medical facilities that reported a pertussis case(s), and the number of reported pertussis cases per reporting medical facility are shown in Table 2.

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By week 21, 2025, the number of reporting medical facilities reached 4,198, with an average of 5.32 case reports per facility. The large increase in the number of reporting facilities may be partly attributed to the growing interest in respiratory infections following the implementation of acute respiratory infection (ARI) surveillance, which began in week 15, 2025. However, no similar increase has been observed in other respiratory infections during the same period, and the number of reports per facility is well above that seen in the past seven years. These findings suggest a nationwide pertussis outbreak that cannot be fully explained by the increase in the number of reporting medical facilities alone.

In recent years, macrolide-resistant B. pertussis (MRBP), which shows resistance to macrolide antibiotics—the first-line treatment—has become a problem worldwide, including Japan. Since 2024, cases of MRBP infection have been reported from Tokyo, Osaka, Tottori, and Okinawa prefectures. In April 2025, a 1-month-old girl with no underlying conditions died of MRBP infection after developing respiratory failure, pulmonary hypertension, and renal failure. It is important to continue bacteriological and epidemiological analyses to monitor trends in antimicrobial resistance of B. pertussis.

Pertussis activity has been increasing internationally, and since 2021, the number of cases reported to the World Health Organization (WHO) has shown an increasing trend across many regions. On 31 May 2025, the Pan American Health Organization/WHO issued an epidemiological alert following a substantial increase in reports from several countries in the Americas. The Alert calls on member states to strengthen pertussis surveillance and to continue to monitor vaccination coverage, with particular attention to children under 1 year and under 5 years of age.

The number of reported cases of pertussis is likely to continue to increase, and attention should be paid across all age groups. On 21 May 2025, the Expert Council on Promotion of Vaccination released a “Request for vaccination in response to the pertussis epidemic”. As a measure to prevent infection in infants, it is recommended that they receive the 5-in-1 vaccine, which is available as a routine immunization starting at two months of age. People who are in close contact with infants or pregnant women should pay particular attention to preventing droplet and contact infection. Since adolescents and adults may also become infected, maintaining basic infection control measures such as wearing masks, practicing cough etiquette, and handwashing, are of great importance. Furthermore, in cases of persistent cough, pertussis should be considered as a possible cause, and it is important to seek medical attention and take appropriate preventive measures.

For more information and updates on Pertussis, please refer to the following (cited on 28 May 2025, all articles in Japanese, except for WHO and PAHO/WHO links):


Department of Infectious Disease Surveillance
Center for Public Health Action in Applied Epidemiology
Department of Bacteriology II
National Institute of Infectious Diseases, Japan Institute for Health Security

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