[Epidemiological and clinical characteristics of pertussis identified through active surveillance]

Objective: To analyze the epidemiological and clinical characteristics of pertussis cases identified through active surveillance. Methods: Active surveillance for pertussis was conducted in three sentinel hospitals in Yiwu, Zhejiang Province, and Yongcheng, Henan Province. The study population included cases that met the surveillance case definition and sought medical care at outpatient/emergency departments or were hospitalized between June 1, 2021, and May 31, 2022. Samples were collected for bacterial culture and PCR detection. Case information and clinical data were collected. Differences in rates were assessed using the chi-square test or Fisher's exact probability test, and the differences in cough time were compared using the Mann-Whitney U test. Results: Among 1 423 cases of pertussis surveillance, the positive rate of pertussis was 28.11% (400/1 423), with a median age of 5 years (interquartile range: 2, 8). The positive rate in Yongcheng, Henan Province, and Yiwu, Zhejiang Province were 39.27% (216/550) and 21.08% (184/873), respectively; the positive rate of pertussis was highest in July 2021, and the highest positive rate of pertussis was among those aged 10-14. The positive rate of pertussis in hospitalized cases was higher than in outpatient/emergency cases (26.68%) (χ²=4.16, P=0.041). Among the 400 laboratory test-positive cases, the highest proportion of atypical symptom cases was in adults aged 20-59 (43.33%, 13/30). The specificity rates of apnea and worsening nocturnal cough in monitored cases under 3 months of age were 100.00% and 73.81%, respectively. Among monitored cases aged 3 months to 9 years, the proportions of symptoms including worsening nighttime cough (63.00%) and night sweats (4.59%) in test-positive cases were significantly higher than those in the test-negative group (47.77% and 0.56%, respectively), with statistically significant differences (both P<0.05). The specificity rates of worsened nighttime coughing and night sweats were 52.23% and 99.44%, respectively. Conclusions: The active surveillance results for pertussis showed that the 10-14 age group exhibited the highest positivity rate. Active surveillance enhanced the detection rate of pertussis. Among laboratory-confirmed cases, the proportion of atypical symptoms was the highest in adults, suggesting that laboratory testing should be combined to diagnose programs of pertussis. For infants under 3 months, worsening nighttime cough and apnea increase the diagnostic specificity, while for individuals aged 3 to 9 years old, worsening nighttime cough and night sweats increase the diagnostic specificity.