Is the current pertussis incidence only the results of testing? A spatial and space-time analysis of pertussis surveillance data using cluster detection methods and geographically weighted regression modelling

Abstract

BackgroundDespite high vaccination coverage, pertussis incidence in the Netherlands is amongst the highest in Europe with a shifting tendency towards adults and elderly. Early detection of outbreaks and preventive actions are necessary to prevent severe complications in infants. Efficient pertussis control requires additional background knowledge about the determinants of testing and possible determinants of the current pertussis incidence. Therefore, the aim of our study is to examine the possibility of locating possible pertussis outbreaks using space-time cluster detection and to examine the determinants of pertussis testing and incidence using geographically weighted regression models.MethodsWe analysed laboratory registry data including all geocoded pertussis tests in the southern area of the Netherlands between 2007 and 2013. Socio-demographic and infrastructure-related population data were matched to the geo-coded laboratory data. The spatial scan statistic was applied to detect spatial and space-time clusters of testing, incidence and test-positivity. Geographically weighted Poisson regression (GWPR) models were then constructed to model the associations between the age-specific rates of testing and incidence and possible population-based determinants.ResultsSpace-time clusters for pertussis incidence overlapped with space-time clusters for testing, reflecting a strong relationship between testing and incidence, irrespective of the examined age group. Testing for pertussis itself was overall associated with lower socio-economic status, multi-person-households, proximity to primary school and availability of healthcare. The current incidence in contradiction is mainly determined by testing and is not associated with a lower socioeconomic status.DiscussionTesting for pertussis follows to an extent the general healthcare seeking behaviour for common respiratory infections, whereas the current pertussis incidence is largely the result of testing. More testing would thus not necessarily improve pertussis control. Detecting outbreaks using space-time cluster detection is feasible but needs to adjust for the strong impact of testing on the detection of pertussis cases.

Protection against Pertussis in Humans Correlates to Elevated Serum Antibodies and Memory B Cells

“…Awareness among physicians about pertussis circulation has led to increased suspect of the disease in patients with persistent coughing and, consequently, to a more frequent testing. It has been shown that B. pertussis infects subjects of all ages who act as infection source causing local clusters of disease ( 28 ). Adults and adolescents may be unaware of being infected by B. pertussis as they experience mild symptoms, difficult to distinguish from those caused by other respiratory infections.…”

Vaccination against Paediatric Respiratory Pathogens

“…Moreover, earlier waning of protective immunity and the circulation of B. pertussis variants depleted of vaccine-included antigens further favor the increase in pertussis disease [74]. Studies in immunized children have reported that antibody responses and protective immunity wane 3-5 years after immunization with acellular pertussis (aP) vaccines, which may reflect poor induction of memory T and/or B cells [76][77][78].…”

Spatio-temporal analysis of Pertussis using geographic information system among Iranian population during 2012-2018

“…About 10 million cases of pertussis occur annually in the world, which most of them(about 90 to 95%) occurred in developing countries (7,8). This reported number had an increasing trend in many countries with high coverage of immunization, and the incidence has shifted the adults (9,10). This indicates challenges in controlling this infection (11).…”