Abstract:

Objective To analyze the epidemiological characteristics of pertussis and infection status of household close contacts in Dalian City from 2023 to 2024，providing a basis for formulating prevention and control strategies. Methods Epidemiological data of confirmed pertussis cases in Dalian from 2023 to 2024 and laboratory test results of their household close contacts were collected for descriptive epidemiological analysis. Results From 2023 to 2024，the annual incidence rates of pertussis were 2.95/100 000（218 cases） and 0.46/100 000（35 cases），respectively，with seasonal peaks from July to October. Age-specific incidence rates per 100 000 population were 30.76 for 0-<5 years age groups，13.42 for 5-<10 years age groups，2.64 for 10-<15 years age groups，and 0.08 for ≥15 years age groups. The annual average incidence rate of the 0-<1 years old group was 180.60/100 000（122 cases），of which the cases aged 0-<3，3-<6，and 6-<12 months accounted for 51.64%，40.16% and 8.20%，respectively. 91.95% of the 5-<10 year old group received 4 doses of pertussis containing vaccine，while 96.83%，63.35% and 80.00% of the 0-<3，3-<6 and 6-<12 month old groups had no immunization history，respectively. The positive rates of Bordetella pertussis culture，polymerase chain reaction（PCR） testing，and serum PT-IgG antibody detection in the case were 10.77%，86.15% and 65.38%，respectively. Household contacts showed 1.14% culture-positivity and 31.46% PCR-positivity，with PCR-positivity highest among siblings（50.00%），followed by parents（30.00%），grandparents（36.36%），and caregivers or other nursing relatives（25.00%）. All seven Bordetella pertussis isolates were multi locus sequence typing（MLST） ST-2. Conclusion The incidence of pertussis in Dalian from 2023 to 2024 shows a downward trend，suggesting that the increase of the population's immune level after the high epidemic period can lead to the decline of the incidence rate，and the study on the impact of changes in immune level on the incidence rate can be carried out. It is suggested to accelerate the research and application of domestic tetanus，diphtheria and acellular pertussis combined vaccine（Tdap），while strengthening the prevention and control of clustered epidemics in families and schools.

Key words: Pertussis, Epidemic characteristics, Close contact, Infection circumstances, Polymerase chain reaction, Multi locus sequence typing