Letter to the Editor

162 To the Editor, The incidence of Bordetella pertussis infections has been increasing (1-4). The Centers for Disease Control and Prevention (Georgia, USA) has reported the greatest number of cases since World War II, including epidemics in Washington, Minnesota and Wisconsin (USA) (3,4). Canada has also reported significant increases in disease activity in British Columbia, Ontario and New Brunswick (5-7). Recent studies suggest that pertussis vaccine immunity may not be as long-lasting as previously believed (8). Pertussis often goes undiagnosed in adults, who are often the source of infection for young infants; however, it is children (particularly infants too young to be fully immunized) who typically carry the highest disease morbidity, and the vast majority of pertussis-related deaths occur among infants <1 year of age (9,10). Due to the increased focus on pertussis internationally, as well as the number of infant pertussis cases this year, we reviewed all pediatric hospitalizations due to pertussis at the Winnipeg Children’s Hospital (WCH, Winnipeg, Manitoba) in the past five years. The review was also used as part of a survey-based study of postpartum women to determine potential hurdles to preventive measures for the protection of infants <3 months of age in Manitoba. Children (<18 years of age) with a laboratory-confirmed diagnosis (nucleic acid detection) of pertussis admitted to WCH from January 1, 2007 to December 31, 2011 were included. WCH is the only major tertiary care centre for pediatrics (86 beds) for Manitoba and the regions of eastern Saskatchewan, northwestern Ontario and southern Nunavut, with a total catchment area of >1.2 million people. The cases were identified through a search of medical records using the International Classification of Diseases – Ninth and Tenth Revision codes for pertussis (033.0), in addition to a review of available pediatric infectious diseases consultant service databases. The charts were abstracted for relevant data including age, duration of admission, intensive care unit care, immunization history, sick contacts, symptoms, laboratory results, management and complications. A spreadsheet (Excel 2007, Microsoft Corporation, USA) was used for descriptive statistics. Forty-two children (18 male) were hospitalized due to pertussis, all were <1.5 years of age and from various regions in Manitoba. The mean age at admission was 83 days. The interquartile range (IQR) was 27.75 to 80.75 days of age at admission. The most common symptom at presentation was cough (86% of cases; mean duration of nine days; IQR four to 13.3 days) (Figure 1). In 21 (50%) of the cases, patients had a sick contact at home; however, their symptoms were most often unspecified. Only three of these were stated to have experienced a cough illness, of whom two were tested and found positive for pertussis. Of these 21 cases, the most frequently reported sick contacts were siblings (60%) and the mother (33%). Twenty-four children (55%) were <2 months of age and, therefore, had not received their first diptheria, tetanus, acellular pertussis (DTaP) dose. Only two children had received their second primary series dose and only one received the full three doses. Most (67%) were admitted to the ward and 33% to the perinatal intensive care unit either on presentation or shortly after admission. The mean length of admission was 17 days (IQR five to 21.5 days). All patients were treated with a full course of a macrolide (either azithromycin for five days or erythromycin for 14 days), except one patient in whom the treatment was unspecified. Many patients (60%) required supplemental oxygen. Complications identified included respiratory failure requiring intubation and ventilation (24%), dehydration requiring intravenous fluids (19%) and hernia (2%). The mean length of intubation was 6.3 days, with an IQR of two to seven days. There were no deaths during the study period, although one involving a four-week-old infant did occur outside the study period in the summer of 2012. Our review of children hospitalized with pertussis at WCH demonstrated that all cases occurred in very young infants, with most too young to have received their primary immunization series. These infants, on average, experienced considerable lengths of stay in hospital, with one-quarter requiring intubation and mechanical ventilation. These infants frequently had exposure to an ill household contact. A limitation of our retrospective review was the frequent lack of confirmation of pertussis or immunization status in these contacts. In addition, our sample sizes were small and may be a reflection of a single-centre review. Despite these aspects, the review reinforces the fact that young infants are at greatest risk for severe morbidity and mortality from pertussis. Our centre’s experience would appear to mirror what has been described across Canada following implementation of acellular pertussis immunization programs, although we did not review the pre-acellular vaccine era. Bettinger et al (11) noted that data from the Immunization Monitoring Program ACTive (IMPACT) surveillance network revealed a shift in the pertussis epidemiology following this change. After 1999, the incidence decreased in children <5 years of age as well as the reported numbers of pertussis-associated encephalitis cases. In the same period, there was an increase in the proportion of cases <3 months of age. One notable difference in our review was that the mean length of admission was almost double, while length of intensive care unit stay was similar. This difference was also apparent when compared with IMPACT data collected before 1997 (12). This may be due to differences in patient populations, comorbid conditions or local practice patterns. There continues to be a need to devise and implement strategies to protect these most vulnerable of patients. Ideally, this should involve increasing herd immunity through several approaches. Maintaining high levels of coverage with DTaP in children and Tdap in adolescents, as well as improving on the extremely poor uptake of Tdap in adults should be priorities (13). Waning of vaccine immunity may require changes in the schedule of boosters (8). ‘Cocooning’ of newborn infants by immunizing all close adult contacts postpartum has been recommended by the Advisory Committee on