Elsevier

Vaccine

Volume 31, Issue 4, 11 January 2013, Pages 618-625
Vaccine

Review
Sources of pertussis infection in young infants: A review of key evidence informing targeting of the cocoon strategy

https://doi.org/10.1016/j.vaccine.2012.11.052Get rights and content

Abstract

Background

The relative contribution of different categories of contact in transmitting pertussis to very young infants, who experience the most severe morbidity, is the most important single factor determining the likely benefit of pertussis vaccination of their close contacts (the “cocooning” strategy).

Objective

To identify, evaluate the quality of and summarise existing data on potential sources of infant pertussis infection in high income countries, focussing on infants under 6 months old.

Data sources: Online databases MEDLINE and EMBASE. Additional studies were identified from the reference lists of relevant articles.

Study selection and analysis: Study quality was evaluated by standardised criteria, based on the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement. Pooled estimates of the proportion of pertussis cases attributable to various contact sources were calculated using data from the highest quality studies.

Results

Nine studies met the inclusion criteria; seven included data on contacts of hospitalised infants less than 6 months old. Case definitions and methods of contact ascertainment were variable. Most identified sources were from the household, of which 39% (95%CI 33–45%) were mothers, 16% (95%CI 12–21%) fathers, and 5% (95%CI 2–10%) grandparents. Estimates for siblings (16–43%) and non-household contacts (4–22%) were more heterogeneous. For 32–52% of infant cases, no source was identified. Asymptomatic pertussis infection was found in 8–13% of contacts evaluated.

Conclusions

These data suggest that the greatest potential impact of pertussis vaccination of adults to prevent severe disease in young infants comes from vaccinating mothers, followed by fathers, with grandparents having a minor role. Siblings varied in importance and, given recent data regarding waning immunity in vaccinated children, need further study. Non-household sources are also well documented, highlighting the potential limitations of the cocoon strategy to prevent severe infant disease.

Highlights

► Literature review and pooled data analysis on infant pertussis infection sources. ► Parents were an important source of pertussis infection in very young infants. ► Grandparents were seldom implicated in infant pertussis infection. ► Siblings play a role as pertussis a source, but data is heterogeneous. ► Parents should be the focus of post-partum pertussis immunisation.

Introduction

The introduction of extensive childhood vaccination programmes during the 1940s and 1950s led to a significant reduction in the incidence of pertussis disease in infants in many countries. Despite this reduction, pertussis remains endemic in populations with high vaccine coverage, and continues to affect young infants, particularly those too young to have completed the primary vaccination course [1], [2]. Waning immunity in adolescents and adults was identified as a significant factor in transmission to young infants over 30 years ago [3], [4]. It is, however, often difficult to identify a source of infection for infants with pertussis, and studies addressing this vary in setting and in the comprehensiveness of evaluation.

The cocooning strategy was identified by the Global Pertussis Initiative (GPI) in 2005, and implementation recommended for countries where it is economically feasible [5], [6]. The aim of “cocooning” – the immunisation of close contacts of young infants – is to protect infants under six months of age who are too young to be fully vaccinated against pertussis and most vulnerable to severe pertussis disease if infected. Various versions of the cocooning strategy have been recommended in Australia, France and Germany [7], [8]. In the United States, cocooning was initially recommended by the Advisory Committee on Immunisation Practices (ACIP) as preferred to maternal immunisation [9] but recently the order of preference was reversed, largely related to the logistic challenges of delivering cocoon programmes [10], [11]. However, immunisation of adult contacts continues to be recommended in the US and elsewhere [8], [11], despite existing challenges in implementation and the lack of strong empirical evidence regarding effectiveness. It is therefore crucial to have high-quality estimates of the proportion of infant infections acquired from various contacts who are the target of a cocooning strategy, in order to inform vaccination policy.

The aim of this literature review was to (1) critically evaluate and summarise the strengths and weaknesses of evidence on the importance of potential household sources (contacts) of pertussis infection, and (2) calculate the relative proportions of infants infected by various household contact categories using estimates from high quality studies conducted in developed countries.

Section snippets

Search strategy

The online databases MEDLINE and EMBASE were searched for all studies published between January 1999 and October 2010 of contacts of infants with pertussis, either clinically diagnosed or laboratory–confirmed. Additional studies were also identified from the reference lists of relevant articles. Search terms to identify studies that included information on infant contacts as sources of disease transmission were included. The search terms were “Diphtheria-Tetanus-acellular-Pertussis Vaccines”,

Study identification and quality

Appendix 1 details the results of the literature search. Of the 15 papers assessed for inclusion, six were excluded due to location, or not providing specific sources of infection for infants less than six or 12 months old. Of the nine included studies listed in Table 1, seven presented data on hospitalised infants less than 6 months of age. The doctoral thesis underpinning one of these studies was also reviewed for additional data [14]. Four of the seven studies were assigned a quality score

Infant age

Two of the nine studies examined patterns of presumptive contact by age strata among infants less than 6 months of age. In Australia, 0–7 week, 8–15 week and 16–23 week old infants were progressively less likely to have been infected by a parent (χ2 trend, P= 0·07)[20]. In the United States, mothers were 2·0 (95% CI 1·1–3·8) times more likely to have been identified as the source of infection for infants aged 0–3 months than for infants aged 4–11 months (P = 0·01)[1]. In the only study of

Discussion

The majority of identified sources of infant pertussis infection were from the household. All of the studies reported either parents or siblings as the most commonly identified source of infection for infant pertussis cases. When taken together, 55% (95% CI 52%–58%) of identified sources of infant pertussis infection was a parent, with mothers approximately twice as likely as fathers to be source. Importantly, this review has allowed for pooled estimates from high quality studies to be

Acknowledgments

The authors gratefully acknowledge Catherine King for her contribution to the development of our search strategies, and Drs Natasha Crowcroft and Sabine De Greeff for providing clarification of data.

Contributors: KE Wiley participated in identifying relevant studies, lead study quality assessment, analysing the data and writing the manuscript. Y Zuo participated in identifying relevant studies, data extraction and assisted in manuscript preparation. KK Macartney and PB McIntyre provided

References (34)

  • K.D. Forsyth et al.

    Prevention of pertussis: recommendations derived from the second Global Pertussis Initiative roundtable meeting

    Vaccine

    (2007)
  • F.R. Mooi et al.

    The case for maternal vaccination against pertussis

    Lancet Infect Dis

    (2007)
  • K.M. Bisgard et al.

    Infant pertussis: who was the source?

    Pediatr Infect Dis J

    (2004)
  • P. McIntyre et al.

    Pertussis in early infancy: disease burden and preventive strategies

    Curr Opin Infect Dis

    (2009)
  • J.D. Nelson

    The changing epidemiology of pertussis in young infants the role of adults as reservoirs of infection

    Am J Dis Child

    (1978)
  • A. Wendelboe et al.

    Duration of immunity against pertussis after natural infection or vaccination

    Pediatr Infect Dis J

    (2005)
  • K. Forsyth et al.

    Potential strategies to reduce the burden of pertussis [Review] [54 refs]

    Pediatr Infect Dis J

    (2005)
  • F. Blangiardi et al.

    Reducing the risk of pertussis in newborn infants

    J Prev Med Hyg

    (2009)
  • National Health Medical Research Council

    Australian immunisation handbook

    (2008)
  • K. Kretsinger et al.

    Preventing tetanus, diphtheria, and pertussis among adults: use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine – recommendations of the Advisory Committee on Immunization Practices (ACIP) and recommendation of ACIP, supported by the Healthcare Infection Control Practices Advisory Committee (HICPAC), for use of Tdap among health-care personnel

    MMWR: Morbidity & Mortality Weekly Report

    (2006)
  • L.A. Castagnini et al.

    Impact of maternal postpartum tetanus and diphtheria toxoids and acellular pertussis immunisation on infant pertussis infection

    Clin Infect Dis

    (2012)
  • Centers for Disease Control and Prevention. Updated Recommendations for Use of Tetanus Toxoid, Reduced Diphtheria...
  • J.P. Vandenbroucke et al.

    Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration

    PLoS Medicine/Public Library of Science

    (2007)
  • B.C. Wallace et al.

    Meta-Analyst: software for meta-analysis of binary, continuous and diagnostic data

    BMC Med Res Methodol

    (2009)
  • Crowcroft N. Estimating the burden of Bordetella pertussis infection presenting to paediatric intensive care units and...
  • N.S. Crowcroft et al.

    Severe and unrecognised: pertussis in UK infants.[Erratum appears in Arch Dis Child. 2006 May;91(5):453]

    Arch Dis Child

    (2003)
  • S.C. de Greeff et al.

    Pertussis disease burden in the household: how to protect young infants

    Clin Infect Dis

    (2010)
  • Cited by (161)

    • Pertussis outbreak in children hospitalized in Rabat (Morocco)

      2024, Diagnostic Microbiology and Infectious Disease
    • Circulation of Bordetella pertussis in vaccinated Cambodian children: A transversal serological study

      2021, International Journal of Infectious Diseases
      Citation Excerpt :

      The most severe cases of pertussis occur in young infants, particularly in those aged <3 months who have not yet started their primary vaccination. However, due to waning immunity induced by the vaccine or by natural infection, pertussis has been recognized to be an important cause of morbidity in older children, adolescents and adults, which in turn represents a source of contamination for infants (Jenkinson, 1988; Wiley et al., 2013; Zepp et al., 2011). To better control the circulation of the pathogen, the WHO recommends several booster doses in a lifetime, including in toddlers and children (World Health Organization, 2015b).

    • Effect of a postpartum prescription for pertussis vaccine: a before-and-after study

      2021, Journal of Gynecology Obstetrics and Human Reproduction
    View all citing articles on Scopus
    View full text