ReviewSources of pertussis infection in young infants: A review of key evidence informing targeting of the cocoon strategy
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)
- et al.
Prevention of pertussis: recommendations derived from the second Global Pertussis Initiative roundtable meeting
Vaccine
(2007) - et al.
The case for maternal vaccination against pertussis
Lancet Infect Dis
(2007) - et al.
Infant pertussis: who was the source?
Pediatr Infect Dis J
(2004) - et al.
Pertussis in early infancy: disease burden and preventive strategies
Curr Opin Infect Dis
(2009) The changing epidemiology of pertussis in young infants the role of adults as reservoirs of infection
Am J Dis Child
(1978)- et al.
Duration of immunity against pertussis after natural infection or vaccination
Pediatr Infect Dis J
(2005) - et al.
Potential strategies to reduce the burden of pertussis [Review] [54 refs]
Pediatr Infect Dis J
(2005) - et al.
Reducing the risk of pertussis in newborn infants
J Prev Med Hyg
(2009) Australian immunisation handbook
(2008)- 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)
Impact of maternal postpartum tetanus and diphtheria toxoids and acellular pertussis immunisation on infant pertussis infection
Clin Infect Dis
Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration
PLoS Medicine/Public Library of Science
Meta-Analyst: software for meta-analysis of binary, continuous and diagnostic data
BMC Med Res Methodol
Severe and unrecognised: pertussis in UK infants.[Erratum appears in Arch Dis Child. 2006 May;91(5):453]
Arch Dis Child
Pertussis disease burden in the household: how to protect young infants
Clin Infect Dis
Cited by (161)
Pertussis outbreak in children hospitalized in Rabat (Morocco)
2024, Diagnostic Microbiology and Infectious DiseaseAssociation between social vulnerability and influenza and tetanus-diphtheria-acellular pertussis vaccination in pregnant and postpartum individuals
2022, American Journal of Obstetrics and Gynecology MFMCirculation of Bordetella pertussis in vaccinated Cambodian children: A transversal serological study
2021, International Journal of Infectious DiseasesCitation 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