Clinical presentation of pertussis in fully immunized children in Lithuania

BMC Infectious Diseases Clinical presentation of pertussis in fully immunized children in Lithuania Irena Narkeviciute 2 Ema Kavaliunaite 2 Genovaite Bernatoniene 1 Rimantas Eidukevicius 0 0 Department of Mathematics and Informatics, Vilnius University , Naugarduko 24, 03225 Vilnius , Lithuania 1 Laboratory of Microbiology, Vilnius University Children's Hospital , Santariskiu 4, 08406 Vilnius , Lithuania 2 Center of Pediatrics, Clinic of Children's Diseases, Vilnius University , Santariskiu 4, 08406 Vilnius , Lithuania Background: In Lithuania, the vaccination coverage against pertussis is high. Nevertheless, there is a significant increase in pertussis cases in fully immunized children. The aim of our study was to determine the frequency of classical symptoms of laboratory confirmed pertussis and describe its epidemiology in children fully vaccinated against pertussis. Methods: From May to December 2001, 70 children aged 1 month to 15 years, suffering from prolonged cough were investigated in the Centre of Paediatrics, Vilnius University Children's Hospital. The collected information included personal data, vaccination history, clinical symptoms of the current illness, and treatment before hospitalization. At the admission to the hospital blood samples were taken from all studied children for Bordetella pertussis IgM and IgA. Results: A total of 53 (75.7%) of the 70 recruited patients with prolonged cough showed laboratory evidence of pertussis. 32 of them were fully vaccinated with whole cell pertussis vaccine (DTP). The age of fully vaccinated patients varied from 4 to 15 years (average 10.9 3.1; median 11). The time period between the last vaccination dose (fourth) and the clinical manifestation of pertussis was 2.6-13 years (average 8.9 3.0; median 9). More than half of the children before the beginning of pertussis were in contact with persons suffering from long lasting cough illness in the family, school or day-care center. The mean duration from onset of pertussis symptoms until hospitalization was 61.4 68.3 days (range, 7 to 270 days; median 30). For 11 patients who had had two episodes (waves) of coughing, the median duration of cough was 90 days, and for 21 with one episode 30 days (p < 0.0002). Most of the children (84.4%) had paroxysmal cough, 31.3% had posttussive vomiting, 28.1% typical whoop, and 3.1% apnea. Only 15.6% children had atypical symptoms of pertussis. Conclusion: Fully vaccinated children fell ill with pertussis at the median of 11 years old, 9 years following pertussis vaccination. More than half of the children could catch pertussis at home, at school or day-care center. Clinical picture of pertussis in previously immunized children is usually characterized by such classical symptoms as prolonged and paroxysmal cough, rarely by whopping and post-tussive vomiting, and very rarely by apnea. - Background Pertussis is a highly communicable, vaccine-preventable respiratory disease. The incidence of pertussis has been greatly reduced by massive vaccination. Nevertheless, there is a significant increase in pertussis cases in older children, adolescents and adult people [1-4]. Improved diagnosis, awareness of pertussis, genetic Bordetella pertussis changes and waning of vaccine-induced immunity are the possible reasons for increased incidence of pertussis [1-5]. In the USA the incidence of vaccine-preventable diseases such as measles, rubella, mumps, diphtheria, tetanus has been greatly reduced in the last 15 years. However, the incidence of pertussis cases increased more than twice: 8296 reported cases in 2002 versus 3450 in 1988 [6]. The age distribution of patients with pertussis in the USA in 19941996 and 19972000 has changed. During the last period, the incidence of pertussis among infants increased by 11%, in children aged 14 years decreased to 8%, remained stable for children aged 59 years and among adolescents and adults increased by about 60% [7]. In Lithuania immunization of infants and children against pertussis has been introduced since 1956 and massive vaccination started in 1961. According to our standard vaccination schedule, pertussis whole-cell vaccine incorporated in diphtheria-tetanus-pertussis (DTP) vaccine is offered at 3, 4.5 and 6 months of age with a booster dose only at 18 months of age. In 1991, the vaccine coverage among children aged 1 year was 73.2%, whereas this percentage has been increasing and since 1996 reached above 90% (93.6% in 2000, 94.6% in 2001). 35% of all pertussis cases were diagnosed in vaccinated children (at least three DTP vaccine doses) during the period from 1991 to 1995, 33.4% of the cases from 1996 to 2000 and 43.2% in 2001. Clinical presentation of pertussis in unvaccinated children had been extensively described by several authors [8,9]. The disease in these patients is usually typical and often severe. Data of the clinical course of pertussis in fully immunized children is usually atypical and generally mild [10]. The aim of our study was to determine the frequency of classical symptoms of laboratory confirmed pertussis and describe its epidemiology in fully vaccinated children. Methods From May to December 2001, 70 children aged 1 month to 15 years with prolonged cough (duration 14 days) and siblings with shorter duration cough (but not less than 7 days) were hospitalized and investigated at Vilnius University Children's Hospital, Centre of Paediatrics. The patients were referred to the hospital by general practitioners or pediatricians, because detailed investigation of the children with prolonged cough of unknown etiology was only available in the hospital. The data regarding to the patient's age, vaccination history, clinical symptoms and signs of the current illness, previous treatment was collected on to computer database. Single blood samples were taken from all the children upon admission and sent for detection of specific immunoglobulin (Ig) IgM and IgA antibodies to B. pertussis by an enzyme-linked immunosorbent assay (ELISA). Serological tests were performed and estimated according to the manufacturer's instructions (Labsystems, Finland). Specimens for B. pertussis and B. parapertussis culture were not obtained because of the late illness stage and received previous antimicrobial therapy before hospitalization. Classical symptoms of pertussis were defined as a prolonged cough lasting two weeks or more, paroxysmal cough, inspiratory whoop, post-tussive vomiting and apnea. Confirmed case of pertussis was defined as an episode of cough lasting 7 days or more and positive anti-B. pertussis IgM or IgA or both levels. Two groups of our studied patients were compared. One group of children with prolonged cough who had two episodes (waves) of successive coughing (when first episode was not ended, it means that cough become more intensified and coughing paroxysm renewed) was compared to the second group who had only one episode of prolonged cough. The descriptive values were (...truncated)