E. Savickienė, D. Razmuvienė, S. Čaplinskas
Centre for Communicable Diseases and AIDS, Vilnius, Lithuania
Citation: Savickienė E., Razmuvienė D., Čaplinskas S. Pertussis epidemiology in Lithuania, 2006 – 2010. EpiNorth 2012;13:35-9.
Pertussis is highly communicable respiratory disease that causes a high morbidity among children. The incidence of pertussis infection in the neighbouring countries (Belarus, Lithuania, Latvia, Poland) was similar to that in Lithuania except in Estonia where the incidence of pertussis is the highest in the Baltic States. The objective of this study was to describe the epidemiology of pertussis in Lithuania in 2006-2010 using case-based reporting data. Incidence increases are observed every four years. The mean annual incidence in Lithuania is 4.9 cases per 100,000 population. The highest incidence was observed in 2009 (6.9 cases per 100,000 population). Infection is common among both vaccinated and non-vaccinated persons. Pertussis incidence was higher among vaccinated than among unvaccinated persons for almost all ages. The highest incidence in the unvaccinated group was among children less than 1 year of age who were too young to be vaccinated. The highest incidence among vaccinated persons was seen in the age groups from ten and fourteen years and from fifteen to nineteen years. More than 80 percent of the cases among vaccinated persons had received at least three doses of the pertussis vaccine. Immunization against pertussis in Lithuania, as it is in other EU countries, led to an observed decline in incidence among younger children. Despite high vaccination coverage whooping cough is becoming a contagious disease of older children and adults due to the lack of long-lasting vaccine-induced immunity.
The notification of pertussis has been mandatory in Lithuania since 1957. At the national level, monthly data in an aggregated format are reported and analyzed by age group, gender and municipality. More specific data are analyzed annually by age group, laboratory confirmation and vaccination status. Case-based reporting with basic epidemiologic data began in 2004.
Immunization using whole-cell diphtheria-tetanus-pertussis vaccine was introduced in Lithuania in 1956. Routine childhood vaccination led to a reduction in number of pertussis cases from thousands to hundreds. The national immunization programme switched from whole cell pertussis vaccines to the acellular vaccine in 2007, and a booster dose against diphtheria-tetanus-pertussis for children of pre-school age was added to the vaccination programme at the beginning of 2008. Currently, the national childhood vaccination schedule recommends the administration of primary vaccination at the age of two, four and six months. A fourth dose is recommended at the age of eighteen months and the fifth and final dose at six-seven years of age (1,2).
During 2006-2010 the incidence of pertussis infection in the neighbouring countries (Belarus, Estonia, Lithuania, Latvia, Poland) was similar except in Estonia where the highest incidence was observed. The incidence of pertussis increased every year from11.4 cases per 100,000 population in 2006 to 96.6 in 2010 (3). In Lithuania in 2010 the incidence of pertussis infection was higher than in Latvia (0.4 cases per 100,000 population) but lower than in Belarus (1.2 cases per 100,000 population), Poland (3.3 cases per 100,000 population) and Estonia (96.6 cases per 100,000 population) (Fig. 1).
The objective of this study was to describe the epidemiology of pertussis in Lithuania in 2006-2010.
Fig. 1. Incidence of pertussis in Lithuania and the neighbouring countries, 2006-2010
Data were obtained from the Centre for Communicable Diseases and AIDS (CCDA), an organization responsible for the surveillance of infectious diseases that used a paper-based annual reporting system through 2009 and an electronic disease reporting system from 2010. Data is reported continuously via the electronic reporting system from the Territorial Public Health centres that receive information from hospitals or health care institutions. Detailed epidemiological data on pertussis were collected retrospectively from 2006 to 2010. Age-specific incidence was calculated using the population estimates from Statistics Lithuania.
A total of 326 cases of pertussis were reported to the CCDA from the ten administrative districts in Lithuania that provided epidemiological data based on the mandatory notification system covering the total population of the country from 2006 to 2010. This corresponds to a mean annual incidence of 4.9 cases per 100,000 inhabitants. Primary pertussis vaccination coverage reaches more than 94 percent annually. Vaccination coverage began to rise from 2006 to 2009, 94.1 and 97.4%, respectively, and in 2010 declined to 94.8%.
Analyzing the incidence in 2001-2010 we observed that three pertussis incidence peaks occurred every fourth year: the first in 2001, the second in 2005 and the third in 2009 (Fig. 2). The highest incidence of 6.9 cases per 100,000 inhabitants was observed in 2009. The lowest incidence of 0.1 cases per 100,000 inhabitants was reported in 2003 (4,5).
Fig.2. The incidence of pertussis in Lithuania, 2001-2010
The age range of cases reported from 2006 to 2010 was between zero and 75 years. There was a dominance of female cases in all age groups. The ratio male to female cases was 0.7. The incidence was highest among infants (118 cases per 100,000) and 82.1% of the cases were among infants under the age of six months. The distribution of the number of cases by age group showed that most pertussis cases, 105 (32%) were among children between ten and fourteen years and 98 cases (30.1%) were among fifteen to nineteen years olds (Tab. 1). Thirty nine (11.9%) cases were among children under one year of age, 36 (11.0%) cases among five to nine year olds and 28 (8.5%) cases were among children aged one to four years. Only 20 (6%) cases were among persons older than 20 years (4, 5).
Table 1. Number (n) of whooping cough cases and mean annual incidence (MAI) by age group in Lithuania, 2006-2010
The vaccination status was known for 309 (94.8%) cases. Eighty three cases (26.8%) were among unvaccinated individuals. Most of the unvaccinated cases (30 cases; 36%) were under one year of age. In older age groups the number of unvaccinated cases decreased to 2 (2.4%) among twenty to twenty four year olds. The number of cases among vaccinated individuals increased from 2 (1.1%) among those under one year of age to 80 (42.1%) among those between ten to fourteen years of age. Among the vaccinated cases only 14 (4.5%) cases were vaccinated with one dose. 210 (67.9%) were vaccinated with at least two doses, of which 190 (90.5%) had completed the primary vaccination series and had received more than three doses. Two cases (0.6%) were vaccinated but number of doses is unknown. Seventeen cases (5.2%) had an unknown vaccination status. The largest number of cases with an unknown vaccination status, 11 (64.7%), were 30 years of age and older.
Fig. 3. Proportion of reported pertussis cases by vaccination status and age group in Lithuania, 2006-2010
Forty one cases (12.6%) were confirmed clinically and 88% (287) laboratory confirmed of which 8.4% were confirmed microbiologically (27 cases) and 73.5% serologically (211 cases) of all of the cases reported from 2006 to 2010.
Vaccination coverage was stable and high from 2006 to 2010. Incidence peaks of pertussis occur periodically and suggest that B. pertussis is circulating in Lithuania. The highest morbidity was reported in 2009 and is related to better diagnostics and an increased awareness among the public.
During 2006 to 2010, the highest incidence of pertussis was among children under one year of age who were too young to be vaccinated or vaccinated incompletely, and among fully vaccinated children from ten to nineteen years of age. The rise in the number of pertussis cases among older age groups is probably due to a waning of vaccine-induced immunity (5), as a result, the last booster dose given to children of pre-school age was added to the vaccination programme in 2008.
While the number of microbiological case confirmations remained relatively stable, serological case confirmation has become considerably more frequent in recent years.
In conclusion, there is a need to raise awareness about pertussis on a local level and strengthen the current epidemiological surveillance system. Most important is timely vaccination of children, maintaining high vaccination coverage and improving laboratory diagnostics. According to ECDC guidelines, it might be advantageous to introduce a pertussis booster dose for adolescents and adults to maintain a high level of immunity and ensure indirect protection to infants (5).
1. Lithuanian National Immunization Programme 2009-2013, order of the Minister of Health No.V-242, signed 31 March, 2009. Available from: http://www3.lrs.lt/pls/inter3/dokpaieska.showdoc_l?p_id=340907&p_query=&p_tr2=
2. Lithuanian pertussis epidemiological surveillance, prevention and control recommendations, 2009
3. EpiNorth, EpiNorth data. Available from: http://www.epinorth.org/eway/default.aspx?pid=230&trg=Area_5279&MainArea_5260=5279:0:15,2937:1:0:0:::0:0&Area_5279=5291:44530::1:5290:1:::0:0&diseaseid=26
4. Lithuanian Centre for Communicable Diseases and AIDS. Statistical report form No. 4. Morbidity of infectious diseases. Available from: http://www.ulac.lt/ataskaitos
5. European Centre for Disease Prevention and Control (ECDC) Guidance. Scientific Panel on Childhood Immunisation Schedule: Diphtheria-tetanus-pertussis (DTP) vaccination. 2009. Available from: http://www.ecdc.europa.eu/en/publications/Publications/0911_GUI_Scientific_Panel_on_Childhood_Immunisation_DTP.pdf