EPIDEMIOLOGICAL STUDY OF PERTUSSIS IMMUNIZATION EFFECTIVENESS IN VARNA REGION ( 2009-2014 )

Gabriela Tsankova1, Eliana Ivanova2, Tatina Todorova1, Rumen Konstantinov2, Neli Ermenlieva3, Ianka Draganova4 1) Department of Preclinical and Clinical Sciences, Faculty of Pharmacy, Medical University Varna, Bulgaria 2) Department of Hygiene, Disaster Medicine and Epidemiology, Faculty of Public Health, Medical University Varna, Bulgaria, 3) Medical college Varna, Medical University Varna, Bulgaria, 4) Regional Health Inspectorate Varna, Bulgaria Journal of IMAB Annual Proceeding (Scientific Papers) 2016, vol. 22, issue 2 Journal of IMAB ISSN: 1312-773X http://www.journal-imab-bg.org


BACKGROUND
Pertussis, or whooping cough, is an acute infectious disease of the respiratory tract, caused by the bacterium Bordetella pertussis.It can be found only in humans [1].The disease spreads predominantly among children, but adults may also be affected [2].The contagious indexvaries from 70-75% to 90%.Whooping cough is easily transmitted from person to person, mainly through air droplets [3].
The incubation period of pertussis usually lasts for 3-5 days.The clinical course of the illness is divided into three stages: catarrhal stage, paroxysmal stage and convalescent stage.Before pertussis vaccine became availablein the 1940s, more than 200,000 cases of pertussis were reported annually.In spite of high vaccination coverage in western countries pertussis is still a major public health burden because of yearly incidenceswhich continue to increase and the mortality in children under 6 months which reaches 0.2%.About 195,000 deaths in children per year are registered according to the World Health Organization in the developing countries.Most deaths occur among young babies who are either unvaccinated or incompletely vaccinated [4].The spreading of the infection can be stopped only by achieving high immunization coverage in the population (>92%) [5].
In Bulgaria routine pertussis immunization was in-troduced in 1960 with diphtheria, tetanus, whole cell pertussis (DTwP) vaccine in 3 dose schedule [6].In addition to this between 1960 and 1981, two booster doses with whole cell pertussis vaccine were implemented among children at age of 18 months and 4 years respectively.This immunization schedule was used for the next 20 years [7].Acellular pertussis vaccine (DTaP) has been applied asa booster doseat 6 years old children since 2008.Since 2010acellular vaccine was included in the Bulgarian Immunization Calendar to perform the primary immunization and it replaced the whole cellular vaccine that had been used for 50 years [8].According to the Bulgarian Immunization Calendar from 1 April 2010 the pentavalentvaccine Pentaximwas used for vaccination at 2-, 3-, 4-, 16-montholds and Tetraxim was applied at 6-year-olds [9].

PURPOSE
In the current study we analyze the epidemiology and control of pertussis in Varna region from 2009 to 2014.We also try to assess the effectiveness of anti-pertussis immunization in the region.

MATERIAL AND METHODS
We performed a retrospective analysis (2009 -2014) using epidemiological data from Regional Health Inspectorate -Varna.

RESULTS AND DISCUSSION
From 2009 to 2014 the morbidity of pertussis in Bulgaria was between 3.3%000 (2009) and 0.3%000 (2014).During the analyzed period, 29 pertussis cases were reported in Varna region.However only 5 of them were confirmed by microbiology diagnosis and PCR typing.The incidence of pertussis in Varna region has been steadily decreasing for the last six years: in 2009 its total value was 4,35%000 while in 2014 zero cases were registered (Fig. 1).The analy-Due to the difficulty in the etiological confirmation of pertussis disease, the reported morbidity rate cannot be used to assume the real intensity of its epidemiological progress.Only those cases with typical clinical manifestation have been registered.The remaining ones are clas-sis of data showed that from 2010 to 2014 the morbidity in Varna region was lower than the average incidence in Bulgaria.

Fig. 1. Morbidity of pertussis in Varna Region and in whole country
sified as acute respiratory diseases.
The disease has a clear seasonal pattern, as most of the notifications occur during the spring and summer (Fig. 2).

Fig. 2. Seasonal distribution of cases in the study region (on y-axis are presented the number of reported cases)
Table 1 shows the distribution of the patients infected with B. pertussisaccording to their age from 2009 to 2014.B. pertussis infection affects different age groups, but the incidence rate is highest in infantsunder 1 year (12 cases in total), following the group of children at 0-9 years of age (9 cases in total).As mentioned above during 2014 there are not any pertussis cases.The main and most effective mean of pertussis's prevention is the specific immunization.During 2009 -2014 vaccination coverage in infant population with 4 doses ranged between 54.6% and 100%.The lowest vaccination coverage (54.6%) was observed from 1 June 2014 to 31 August 2014, when the supply of vaccines was irregular (Table 2).Surpris-ingly, during the same year the lowest pertussis incidence was also observed mainly due to better immunization coverage in the previous years.The result of the irregular vaccination during the last year of our study will be precisely observed in the near future when an increased number of pertussis cases are expectedto appear in the region.

CONCLUSION
In this study we show that during 2009-2014 Bordetella pertussis infection tends to decrease in Varna region.The reduction in vaccination coverage due to the irregular supply with vaccines and the increasing lack of vac-

Table 2 .
Pertussis immunization in Varna region parents is alarming.Therefore the range and quality of specific immunoprophylaxis should be improved.Thehealth care professionals should have a central role in maintaining public trust in vaccination.