Epidemiological and clinical characteristics of pertussis in pediatric population: a multicenter study of 20,727 children in Hubei, China

Abstract

Background

This study aims to investigate the current epidemiological and clinical features of pertussis among children in Hubei, China, and to provide evidence for optimizing prevention and control strategies.

Methods

From October 2023 to February 2025, nasopharyngeal swabs of altogether 20,727 children with suspected pertussis across multiple hospitals were collected for etiological detection of Bordetella pertussis. Real-time PCR (qPCR) assay was used to confirm diagnosis. Descriptive epidemiological analysis was performed on the results.

Results

Among the study population, 2,523 cases (12.2%) were PCR positive. Seasonal peaks were in spring (49.7%) and winter (25.1%), and the highest incidence occurred in April 2024 (511 cases, 20.3%). PCR positive children were significantly older than PCR negative counterparts (median [IQR] age: 5 [2–7] vs 4 [2–6] years, P < 0.001), while in pertussis cases the inpatients were significantly younger than the outpatients (median [IQR] age: 0 [0–5] vs 6 [4–7] years, P < 0.001). Children aged 5–9 years (around primary school age) were the most affected (1,468 cases, 58.2%), whereas infants aged 0–2 months were most severely hospitalized (48 cases, 27.9%). Alarmingly, the vast majority of pertussis cases are not adequately identified, up to 98.9%.

Conclusions

Our findings indicate a significant epidemiological shift with the primary school age emerging as the new high-risk population for pertussis, necessitating targeted surveillance. These results underscore the urgent need for enhanced clinical awareness, improved diagnostic protocols, and targeted vaccination strategies, particularly for primary school children and infants.

Background

Pertussis is a highly contagious, vaccine-preventable acute respiratory infectious disease caused by Bordetella pertussis. At present China uses DTP (Diphtheria-Tetanus-Pertussis) vaccine to prevent pertussis and the coverage rate remains above 99% [1]. Despite high vaccination rates, there has been a marked resurgence in pertussis cases since 2022 and similar phenomena have also occurred worldwide [2]. Since 2023, a sharp increase in the number of deaths and the atypical epidemic pattern of pertussis have been reported as well [3, 4], which triggered widespread concerns. Up to now, the persistent pertussis resurgence remains unresolved [1].

Among all populations, pertussis demonstrates high susceptibility in children, highlighted by high risks of morbidity and mortality [5], and ranks among the foremost vaccine-preventable causes of childhood death globally [6]. The accelerating prevalence of pertussis not only becomes a grave public health challenge, but also severely threatens the health of children. Thus, studying the distribution pattern of pertussis in children is indispensable for managing the evolving dynamics of pertussis. Here we analyzed the epidemiology and clinical characteristics of pertussis among pediatric population from October 2023 to February 2025 in Hubei Province, hoping to identify the current epidemic situation of pertussis and inform contemporary prevention and control strategies.

Methods

Patients and samples

This is a multicenter cross-sectional study conducted under the leadership of Renmin Hospital of Wuhan University. From October 2023 to February 2025, nasopharyngeal swabs were obtained from 20,727 children (≤ 14 years, both inpatients and outpatients) with suspected pertussis from three tertiary hospitals in Hubei Province (Renmin Hospital of Wuhan University, Tongji Hospital affiliated to Tongji Medical College HUST, and Maternal and Child Health Hospital of Hubei Province). Case information including age, gender, date of onset, treatment method and clinical diagnosis etc. was recorded. Sample analysis was performed by qPCR for detection of Bordetella pertussis. This study was approved by Clinical Research Ethics Committee of Renmin Hospital of Wuhan University.

Collection of nasopharyngeal swabs

Using a flexible shaft minitip flocked or rayon swab, gently insert the swab into a nostril while the patient’s head is tilted back approximately 70 degrees, advancing along the palate until resistance is encountered at the nasopharynx. Hold the swab in place for several seconds, rotating it gently to absorb secretions, then slowly withdraw it while continuing to rotate. Immediately place the collected specimen into a tube containing sterile transport medium and secure the lid. The sample is stored at 4 °C without delay and transported to the laboratory on ice for processing within 24 h.

Etiological detection of Bordetella pertussis

According to the manufacturer’s instructions, DNA was extracted from clinical samples using the pertussis bacillus nucleic acid detection kit (PCR fluorescence probe method) (Shenzhen Yilifang Biotech CO., LTD., China). Applied Biosystems 7500 Real-Time PCR System (Applied Biosystems Inc., USA) was used for detection. The FAM detection channel is for pertussis amplification signal, and the HEX/VIC detection channel is for internal standard amplification signal. If the FAM detection channel has a clear and smooth S-shaped amplification curve, and the Ct value is ≤ 38, then the sample is positive; if there is no Ct value in the FAM detection channel or Ct value > 38, and the Ct value in the HEX/VIC detection channel is ≤ 34, then the sample is negative.

Statistical analysis

We analyzed all data using SPSS 25.0. Categorical variables are presented as case number (%), and group differences were compared using the Chi-square test. For continuous variables—specifically age—we assessed normality with the Kolmogorov–Smirnov test. Since these data were non-normally distributed, we summarized them as median and interquartile range (M [IQR]) and compared between groups using the Mann–Whitney U test (for two groups) or the Kruskal–Wallis H test (for multiple groups), as appropriate. We considered a two-sided P value < 0.05 as statistically significant.

Results

General situation

Throughout the research period, nasopharyngeal swabs were collected from a total of 20,727 children with suspected pertussis in the above-mentioned hospitals, including 11,577 males and 9,150 females (male to female ratio 1.26). The age range was from 1 day to 14 years, with a median [IQR] age of 4 [2–6] years. 2,523 cases (12.2%) were diagnosed with pertussis by positive PCR result.

Demographic characteristics

Among the positive cases, there were 1,396 males and 1,127 females (male to female ratio 1.24) and positive rates between the two genders (male 12.0% vs female 12.3%) were comparable (χ² = 0.320, P = 0.572) (Table 1). Notably, among infant cases (< 1 year), the positive rate of female infants (15.1%) was significantly higher than that of male infants (11.6%) (χ² = 8.754, P = 0.003). It was observed that PCR positive children were significantly older than the PCR negative (median [IQR] age: 5 [2–7] vs 4 [2–6] years, Z = −15.064, P < 0.001). And there was significant difference in the incidence of pertussis between age groups (χ² = 731.925, P < 0.001). The highest case numbers (1,468 cases, 58.2%) and positive rate (19.0%) were both found in the 5–9 years group (around primary school age) (Table 1).

Table 1.

General characteristics of the sample population, from Oct 2023 to Feb 2025

	Negative PCR	Positive PCR		Total	χ 2	P value*
Age (years), M [IQR]	4 [2–6]		5 [2–7]			< 0.001※
Gender	(n = 18,204)		(n = 2,523)		0.320	0.572
Male	10,181(55.9%)		1,396(55.3%)	11,577
Female	8,023(44.1%)		1,127(44.7%)	9,150
Age group					731.925	< 0.001
0–5 months	1,755(9.6%)		319(12.6%)	2,074
6–12 months	1,213(6.7%)		122(4.8%)	1,355
1–4 years	7,864(43.2%)		443(17.6%)	8,307
5–9 years	6,267(34.4%)		1,468(58.2%)	7,735
10–14 years	1,105(6.1%)		171(6.8%)	1,276
Season					321.853	< 0.001
Spring	7,176(39.4%)		1,254(49.7%)	8,430
Summer	4,440(24.4%)		552(21.9%)	4,992
Autumn	2,833(15.6%)		83(3.3%)	2,916
Winter	3,755(20.6%)		634(25.1%)	4,389
Clinical diagnosis	(n = 15,160)		(n = 2,164)
Pertussis	119		23	142
Tracheitis/Bronchitis	2,331		269	2,600
Pneumonia	2,414		180	2,594
Respiratory tract infection	7,471		1,326	8,797
Cough	1,397		241	1,638
Others	1,843		147	1,990
Treatment method	(n = 14,770)		(n = 2,201)		254.179	< 0.001
Outpatient	11,438(77.4%)		2,029(92.2%)	13,467
Inpatient	3,332(22.6%)		172(7.8%)	3,504

^*Chi-square test

^※Mann-Whitney U test

(The counting rule for “Clinical diagnosis” category in Table 1 is as follows: if a given keyword is included in the diagnosis, the diagnostic category will be counted; while if none are included, it will be recorded as “Others”. As a diagnosis may contain more than one disease, the sum of case numbers of each item in the clinical diagnosis category is greater than the sample size of this category in Table 1.)

Positive rates varied significantly across different age groups and exhibited a temporal pattern over the months. In 2024, the positive rate of the 5–9 years remained relatively high throughout the year, with a maximum value (Feb) exceeding 30%, and the positive rate of the 0–5 months (15.4% overall) was also slightly higher than the overall level (12.2%). The rest were all similar to or lower than the overall level (Fig. 1).

Fig. 1.

Positive rate per month and age group (2024)

Figure 2 shows the monthly variation of case numbers and the composition proportion of infant cases from Oct 2023 to Feb 2025. Generally, from Dec 2023 to Oct 2024 when there were relatively large case numbers, the proportion of infant cases wasn’t high and no evident shift occurred either. Combining with Table 1, the overall percentage of infant cases was only 17.4%, indicating that infants are not the main population affected by pertussis nowadays.

Fig. 2.

Monthly distribution of pertussis children aged < 1 year and ≥ 1 year, Oct 2023 – Feb 2025

Seasonal distribution

There were 1,254 pertussis cases (49.7%) in spring (Mar-May), 552 cases (21.9%) in summer (Jun-Aug), 83 cases (3.3%) in autumn (Sep-Nov) and 634 cases (25.1%) in winter (Dec-Feb) (Table 1). The incidence of pertussis was significantly different between seasons (χ² = 321.853, P < 0.001), with the highest case number and positive rate observed in spring (1,254 cases, positive rate 14.9%), followed by winter (634 cases, positive rate 14.4%). From a yearly perspective, the number of pertussis cases increased drastically, reaching its peak in spring (Mar-May, 2024) and then gradually decreased. The maximum frequency occurred in April 2024 (511 cases, 20.3%) (Fig. 2). In 2024, the positive rate of pertussis in children was higher in the first half of the year (winter and spring) (approx 15% overall) and then gradually decreased over time. All the age groups generally corresponded with this trend (Fig. 1).

For infants, pertussis infection showed variations by age in months and seasonal patterns. Among a total of 441 infant cases, pertussis was mainly distributed in the age range of under half a year old (≤ 5 months) with a proportion of 72.3% (Table 1), especially concentrated around 3 months. Among the infant cases of each season, the highest case numbers were found at 3 months old (with the highest overall proportion of 17.9% in infants) (autumn of 2023, spring of 2024, summer of 2024), 2 months old (winter of 2023 and 2024) and 5 months old (autumn of 2024) respectively, while the lowest proportion was at 12 months old (0 case, 0%) (Fig. 3).

Fig. 3.

Age composition (months) of pertussis infants, Oct 2023 – Feb 2025

Clinical diagnosis

Among 2,164 PCR-positive cases with complete clinical diagnostic information, there was a high rate of overlooking (or under-recognition) of pertussis, up to 98.9% (2,141/2,164), with only 23 out of 2,164 pertussis cases (1.1%) definitively diagnosed as pertussis. Most pertussis cases were diagnosed as respiratory tract infection (1,326 cases), tracheitis/bronchitis (269 cases), cough (241 cases) and pneumonia (180 cases), etc. (Table 1).

Distribution of treatment methods

Table 2 shows the hospitalization status of pertussis children in different groups. Among them, 172 cases (7.8%) were inpatients and 2,029 cases (92.2%) were outpatients, and the age of the former was significantly younger than that of the latter (median [IQR] age: 0 [0–5] vs. 6 [4–7] years, Z = −9.640, P < 0.001). And compared with the PCR negative patients, there was a significant difference in the composition of treatment methods (χ² = 254.179, P < 0.001) (Table 1).

Table 2.

Hospitalization status of pertussis cases in different groups

	Outpatient	Inpatient	χ 2	P value*
	(total n = 2029)	(total n = 172)
Age (years), M [IQR]	6 [4–7]	0 [0–5]		< 0.001※
Gender			10.067	0.002
Male	1,139(56.1%)	75(43.6%)
Female	890(43.9%)	97(56.4%)
Age group			324.107	< 0.001
0–2 months	42(2.1%)	48(27.9%)
3–5 months	117(5.8%)	29(16.9%)
6–12 months	96(4.7%)	10(5.8%)
1–4 years	361(17.8%)	29(16.9%)
5–9 years	1,271(62.6%)	45(26.2%)
10–14 years	142(7.0%)	11(6.4%)
Season			24.232	< 0.001
Spring	1,021(50.3%)	79(45.9%)
Summer	416(20.5%)	28(16.3%)
Autumn	54(2.7%)	16(9.3%)
Winter	538(26.5%)	49(28.5%)

^*Chi-square test

^※Mann-Whitney U test

Further analysis revealed that the hospitalization rates varied significantly by gender (χ² = 10.067, P = 0.002), age (χ² = 324.107, P < 0.001) and season (χ² = 24.232, P < 0.001). In terms of gender, the hospitalization rate of females (9.8%) was higher than that of males (6.2%). In terms of age, the 0–2 months had the highest hospitalization rate (53.3%) and proportion (48 cases, 27.9%). And after vaccination age (3–5 months and later) there was a substantial decrease in hospitalization. Although the proportion of hospitalization in the subsequent 5–9 years group was high (45 cases, 26.2%), the hospitalization rate was very low (3.4%). In terms of season, the most hospitalized cases were in spring (79 cases, 45.9%) and followed by winter (49 cases, 28.5%), which was consistent with the seasonal distribution of pertussis incidence.

Discussion

In recent years, the number of pertussis children in China has been increasing year by year, and their origins are widespread and spread throughout various provinces [7]. However, due to insufficient monitoring and identification, the actual incidence rate of pertussis is still seriously underestimated [8]. The resurgence of pertussis is fierce and has become a critical challenge in pediatric infectious disease management [9]. Therefore, investigating the epidemic patterns of pertussis is of significant importance for disease prevention, control, and clinical management.

This study shows that pertussis was more prevalent in children in Hubei Province during winter and spring (around spring), accounting for over 70% of both cases and hospitalizations. While in some studies, the summer predominance of pertussis has also been reported [10, 11]. Considering the time span of this study, the case number in summer was also relatively high (21.9%), so the incidence of pertussis in summer cannot be ignored either. This reflects the long-term transmission and prevalence of pertussis across multi seasons throughout the year that warrants sustained vigilance.

Our study found that pertussis infection may exhibit certain sex-based differences. Specifically, female infants had a higher positive rate than males, and among infected children, females had a higher hospitalization rate than males. We speculate that this may be due to sex-based immunological differences, leading to higher susceptibility to pertussis and possibly more severe inflammatory responses after infection in female children. Additionally, these observed differences could reflect regional characteristics of pertussis transmission.

Among all age groups, children aged 5–9 years (around primary school age) not only had a high number of cases (58.2%) but also a high positive rate (19.0% overall, consistently at a high level throughout the year), while the proportion of cases in the infant population was only less than 20% (17.4% overall). This reflects that the peak susceptibility group for pertussis has shifted to school age children, and other studies in the past two years have also mentioned the phenomenon of the age of peak onset shifting from infancy to school age [12, 13]. The findings of this study further narrow down this scope to primary school age. This phenomenon may be related to the attenuation of vaccine immunity [13] and the lack of universal vaccination for school age children in China before 2025 [11]. The active gathering environment of primary school may also be an important reason for the high incidence and spread of pertussis in this age group. In addition, it was found that there was a high proportion of non-hospitalized samples (92.2%) in pertussis cases, which may suggest that there were a large number of omitted infected school age cases in society. The widespread presence of latent infections among adolescents can make them an important source of infection [14]. Therefore, it should be considered to include primary school age children in the pivotal population for pertussis prevention and control, and to screen, immunize, and educate relevant populations to enhance their awareness of disease defense. In the future, prevention and treatment of pertussis in primary school age children may become a new focus of pertussis management.

The age of pertussis positive children was significantly higher than that of pertussis negative children, which may be due to vaccine immune attenuation leading to susceptibility to pertussis. And the age of hospitalized children with pertussis was significantly younger than that of the outpatients, which is consistent with previous research results, may be due to the mitigation of clinical symptoms of pertussis caused by aging [10]. Infants remain vulnerable, particularly very young infants. Our data indicate that patients aged 0–2 months accounted for the largest proportion (27.9%) of all hospitalized cases, and this group also exhibited the highest hospitalization rate (53.3%) among all age cohorts. This suggests that children aged 5–9 years are more commonly diagnosed with mild symptoms, while those aged 0–2 months have relatively fewer cases but more severe symptoms [15]. This is related to the underdeveloped immune system of young infants [16] and their age being too young to receive vaccinations [17].

This research indicates that pertussis is commonly overlooked in clinical practice, as most confirmed cases (98.9%) were not suspected of having pertussis during their initial medical consultation and were instead managed for other respiratory diagnoses, and this phenomenon occurs in various parts of the country as well [7]. There are multiple possible reasons for this, including a lack of clinical awareness and attention to pertussis [7], confusion in the diagnosis of co-infection or cough-related underlying diseases [15], and similarities in infection symptoms with some atypical pathogens [18, 19]. We should strengthen the training and education of medical personnel and the public to improve their awareness of pertussis, striving for early diagnosis, early control, and prevent the occurrence of serious complications and further spread of the disease.

These years, erythromycin-resistant and highly virulent strains of pertussis have been commonly found in Chinese pertussis patients [20, 21]. This change may increase the difficulty of treating pertussis and result in more serious complications. While exploring new therapies, more attention should be paid to the prevention of immunocompromised population such as infants. Analysis by Hu et al. suggests that a decrease in the proportion of pertussis cases in infants does not equate to a decrease in risk, and as more virulent strains emerge, infants may have a higher risk of mortality [12]. And our research finds that infant infection was mainly concentrated in the 0–5 months age group (72.3%), with the highest incidence occurring in the 3 months. This indicates that infants have a higher risk of pertussis infection from birth to around the first dose of DTP vaccine. Studies have shown that maternal immunization against pertussis is an effective protective strategy for infants under 6 months of age [22], which can significantly reduce the incidence and hospitalization of young infants [23]. However, China has not yet established a policy on maternal immunization against pertussis, and introducing pertussis vaccination during pregnancy should be considered to enhance immunity. In addition, starting from January 1 st, 2025, the new DTP vaccination policy of China has come into effect, and these are two of the changes: advancing the first dose to 2 months old and adding the fifth dose of DTP vaccine at the age of 6 years. This optimization is a significant step in the prevention and control of pertussis in China [24]. The new vaccination strategy of DTP vaccine can provide earlier infant immune protection and supplementary immune protection for school age children. A smooth transition is essential to implement vaccination among the school age and guarantee vaccination coverage in the future.

This study analyzes the epidemiological and clinical characteristics of pertussis among pediatric population in Hubei Province, which has the advantages of large sample size and strong timeliness, reflecting the latest epidemical situation of pertussis in Hubei and even central China, and providing ideas for the improvement and refinement of pertussis prevention and control strategies in various sectors of society. Furthermore, this study has several limitations. Incorporating relevant information such as clinical symptoms and antibiotic usage into further analysis could yield more comprehensive conclusions. Partially missing data for certain variables across different hospitals may introduce potential bias to the results.

In conclusion, pertussis among children in Hubei Province is more prevalent in spring and winter, and has a long duration of prevalence throughout the year. The awareness and vigilance of medical personnel towards pertussis urgently need to be strengthened. The susceptible population has shifted to the primary school age, while infections in young infants are more dangerous. It’s expected that the primary school age children may become a new focus of pertussis management. With the introduction and implementation of the new DTP vaccination strategy, further observation and research are needed on the new epidemic tendency of pertussis in the future.

Authors’ contributions

W.L., J.A.G.SEGBO and Z.J. conducted data collection and management. S.X. and L.Y. designed this study and analyzed the data. All authors interpreted the results. S.X. drafted the manuscript. C.Y. and Z.L. modified and polished the manuscript. C.Z. and Z.J. conceived and guided this study and revised the manuscript. All authors read and approved the final manuscript.

Funding

The Fundamental Research Funds supported this work for the National Key R&D Program of China (2024YFC2309300), the National Natural Science Foundation of China (project no. 82472337), the Open Research Program of the State Key Laboratory of Virology of China (Grant No. 2023KF004, 2022KF003).

Data availability

The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by Clinical Research Ethics Committee of Renmin Hospital of Wuhan University and adheres to the Declaration of Helsinki, and informed consent has been obtained from all participants.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Conflict of interest

The authors declare no conflict of interest.