Pediatr Infect Dis J. 2014 Nov;33(11):1114-8.

Prevalence of antibody to Bordetella pertussis in neonates and prevalence of recent pertussis infection in pregnant women in Catalonia (Spain) in 2003 and 2013.

Plans P, Álvarez E, de Ory F, Campins M, Payà T, Balfagón P, Godoy P, Caylà J, Carreras R, Cabero L, Domínguez A; Pertussis Working Group.

 

From the *Public Health Agency of Catalonia, Catalonia; †CIBER de Epidemiología y Salud Pública (CIBERESP), Instituto de Salud Carlos III, Madrid; ‡Obstetrics Service, Hospital Josep Trueta of Girona, Girona; §Instituto de Salud Carlos III, Madrid; ¶Preventive Medicine and Epidemiology Service, Hospital Vall d’Hebron of Barcelona; ‖Ginaecology and Obstetrics Service, Hospital del Mar of Barcelona; **Public Health Agency of Barcelona; ††Obstetrics Service, Hospital Vall d’Hebron of Barcelona; ‡‡Department of Public Health, University of Barcelona, Barcelona, Spain.

 

Abstract

BACKGROUND: Infections because of Bordetella pertussis still occur in infants and adults in European countries, despite vaccination coverage against pertussis being high.

METHODS: IgG antibody titers to pertussis toxin (anti-PT) were assessed using an enzyme-linked immunosorbent assay test (Serion ELISA classic) in 353 cord blood samples from neonates of a representative sample of pregnant women obtained in Catalonia (Spain) in 2013. Neonates with anti-PT titers ≤ 40 international units (IU)/mL were considered to be unprotected against pertussis. IgG-PT titers >100 IU/mL in umbilical cord samples were considered to be indicative of a current or recent pertussis infection (12 months) in pregnant women. The age-standardized prevalence of recent pertussis infection obtained in this study was compared with the prevalence obtained in 2003.

RESULTS: The mean anti-PT titer in neonates was 10.8 IU/mL and 89.8% of neonates were unprotected against pertussis. The prevalence of unprotected neonates as defined by cord blood anti-PT ≤ 40 IU/mL was 90%. The prevalence of recent pertussis infection in pregnant women as defined by cord blood anti-PT >100 IU/mL was 2%. The diphtheria-tetanus-pertussis vaccination coverage during childhood in pregnant women was 75%. The age-standardized prevalence of recent pertussis infection in pregnant women observed in this study (2.2%) was slightly higher than the prevalence obtained in 2003 (1.5%), with an odds ratio = 1.45 (95% confidence intervals: 0.5-3.9), although differences were not statistically significant.

CONCLUSIONS: Most neonates are unprotected against pertussis and pertussis infections are frequent in pregnant women in Catalonia. Infants and pregnant women should be the priority population groups for pertussis prevention programs in Catalonia.

PMID: 24871642

 

Supplement:

The low mean IgG anti-PT titers (10.8 IU/ml), the high prevalence of unprotected neonates (90%), and the high prevalence of recent pertussis infections in pregnant women (2%) found in the study shows that neonates and pregnant women are vulnerable to pertussis.

The whole cell diphtheria-tetanus-pertussis vaccine (wDTP) introduced in Spain in the 1960s significantly reduced the mortality rates of whooping cough (pertussis) in developed countries. However, Spain and other European countries have experienced increasing pertussis rates and outbreaks in the last 10 years despite higher percentages of vaccinations. The higher age-standardized prevalence of recent pertussis infections in pregnant women found in the study in 2013 as compared to 2003 (2.2.% vs. 1.5%; Odds Ratio=1.65) is consistent with the increase in the incidence of whooping cough observed in Catalonia from 2003 to 2013. The DTP vaccination program reduced the occurrence of pertussis in children in Catalonia, but waning anti-pertussis immunity has permitted the disease to affect adolescents and adults, who can transmit the disease to unprotected pregnant women and infants.

The prevention of whooping cough in infants aged less than 3 months and less than 1 year should be a public health priority in Spain, as well in other developed countries, because they suffer the highest incidence rate, the highest hospitalization rate, and the highest frequency of complications due to the disease. In Spain in 2011, the incidence rate of whooping cough in infants aged less than 1 year was 120 per 100,000, the hospitalization rate was 8.75 per 100,000, and 95% of deaths due to whooping cough occurred in this age group. In infants under 3 months of age, the incidence was 142 per 100,000.

Seroprevalence studies are important to vaccination managers, health planners and epidemiologists because they inform about: the real immunity level in the population and the effectiveness of vaccination programs in terms of immunity levels.1 If the objective is to achieve and maintain sufficient immunity protection in the population to prevent transmission of an infectious agent, seroprevalence studies show whether or not herd immunity can be considered established. The establishment of herd immunity is assessed by comparing the prevalence of positive results observed in a serological survey with the critical prevalence associated with herd immunity.1 Based on this method, when the prevalence of positive results is lower than the critical prevalence, additional vaccinations are recommended to establish herd immunity. For pertussis, the critical prevalence of protected individuals required to establish the necessary herd immunity to block pertussis transmission in the community is 90−94%.1 The critical prevalence of positive seroplogic results associated with herd immunity is 88−91%, assuming 99% sensitivity and 98.5% specificity for the serologic test. The vaccination coverage required to establish herd immunity is 95−99%, assuming 95% vaccine effectiveness. The seroprevalence study carried out in Catalonia in 2013 showed that anti-pertussis immunity levels found in neonates and pregnant women were much lower than those required to prevent pertussis transmission.

The following pertussis immunization strategies can be used to protect pregnant women and neonates against pertussis infections:

  1. Universal immunisation of adolescents and adults.
  2. Immunisation of pregnant women.
  3. Immunisation of mothers and close family contacts of newborns (cocooning).

 

Until 2004, the pertussis immunisation program in Catalonia included five doses of the wDTP vaccine at 2, 4, 6, and 18 months, and at 4-6 years. Beginning this year, the program included five doses of the diphtheria-tetanus-acellular pertussis vaccine (DTaP). Vaccines containing tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis antigens (Tdap) can be used to maintain anti-pertussis immunity in women of childbearing age, adolescents and adults if the are used instead of the anti tetanus and diphtheria (Td) for adults. In January 2013, the Centers for Disease Control and Prevention Advisory Committee on Immunisation Practices (ACIP) of the United States recommended administering a dose of Tdap vaccine to all women during each pregnancy, regardless of immunization history.2 Immunizing women after delivery and close family contacts of newborns is less effective and more costly than immunizing women during pregnancy for preventing pertussis illness in infants aged less than 6 months. In 2014, the Health Department of Catalonia recommended that women receive a booster dose of Tdpa vaccine during the third trimester of pregnancy. Anti-pertussis immunisation during pregnancy provides infants protection by means of preventing pertussis infections in pregnant women and by increasing passive anti-pertussis antibodies in infants. The universal vaccination strategy using Tdap vaccines every 10 years in adolescents and adults should requires 95−99% coverage figures to establish the necessary herd immunity to prevennt pertussis transmission in the community..

The importance of the study is four-fold. First, it shows that pregnant women and neonates can be vulnerable to pertussis infections in countries where wDTP/aDTP vaccines are given only during childhood. Second, it shows that Bordetella pertussis infections can be frequent during pregnancy. Third, it supports the vaccination of pregnant women with dTpa vaccines during the third trimester of pregnancy. Four, it shows that it could be necessary to give dTpa vaccines to adolescents and adults to achieve and maintain high anti-pertussis immunity levels in the population.

 

References

  1. Plans-Rubió P. Evaluation of the establishment of herd immunity in the population by means of serological surveys and vaccination coverage. Human Vaccines & Immunotherapeutics 2012; 8:184-188. Available from: http://www.tandfonline.com/doi/pdf/10.4161/hv.18444
  2. Centers for Disease Control (CDC). Updated recommendations for use of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine (Tdap) in pregnant women – Advisory Committee on Immunization Practices (ACIP). Mortality and Morbidity Weekly Report (MMWR) 2013;62:131–135.

 

Contact:

Pedro Plans-Rubió, M.D., Ph.D., M.Sc.

Responsible for Health Registries, Public Health Agency of Catalonia

Roc Bornat 83-95, 08005 Barcelona, Spain

pedro.plans@gencat.cat

 

 

 

Multiselect Ultimate Query Plugin by InoPlugs Web Design Vienna | Webdesign Wien and Juwelier SchönmannMultiselect Ultimate Query Plugin by InoPlugs Web Design Vienna | Webdesign Wien and Juwelier Schönmann