Registry-Based Surveillance of Influenza-Associated Hospitalisations during the 2009 Influenza Pandemic in Denmark: The Hidden Burden on the Young

To follow the impact of the 2009 influenza pandemic in Denmark, influenza surveillance was extended with a system monitoring potentially influenza-associated hospitalisations.National administrative data from 2004–2010 from the automatic reporting of all hospital visits and admissions in Denmark (population 5.5 million) were used. In-patient hospitalisations linked to ICD-10 codes for potentially influenza-associated conditions (influenza, viral and bacterial pneumonia, respiratory distress, and febrile convulsion) were aggregated by week and age groups; <5 years, 5–24 years, 25–64 years and ≥65 years. Weekly numbers of influenza-associated hospitalisations were plotted to follow the course of the pandemic. We calculated the total numbers of influenza-associated hospitalisations in each influenza season (week 30 to week 15, the following year). Risk ratios of being admitted with an influenza-associated condition in this season (2009/2010) compared to the previous five seasons (2004/2005–2008/2009) were calculated using binary regression. During the pandemic season, influenza-associated hospitalisations peaked in week 47, 2009. The total number of influenza-associated hospitalisations was 38,273 compared to the median of previous seasons of 35,662 (p = 0.28). The risk ratio of influenza-associated hospitalisations during the pandemic season compared to previous seasons was 1.63 (95%CI 1.49–1.78) for 5–24 year-olds and ranged between 0.98 and 1.08 for the other three age groups.The 2009 pandemic influenza did not lead to an overall increase in the number of influenza-associated hospitalisations in Denmark in the 2009/2010 season and could be managed within existing hospital capacity. However, there was a disproportionally large impact on the age group 5–24 years. The influenza-associated hospitalisations during the 2009/2010 pandemic influenza season bore the signature features of historical pandemics: A skewed age-pattern and early out of season transmission

The epidemiology of varicella zoster virus disease in Sweden : before and after vaccination

Primary infection with the varicella zoster virus (VZV) presents as chickenpox, a highly contagious infection. Thereafter the virus establishes latency in nerve ganglia of the host. The virus may reactivate later in life and cause shingles, neurological and/or visceral complications. The overall aim of this thesis was to provide a baseline for the burden of chickenpox disease in Sweden and to assess the impact of vaccination on the epidemiology of VZV disease in order to contribute knowledge to an appraisal of general vaccination against the diseases in Sweden carried out by the Public Health Agency. In Study I, we obtained data from healthcare registers and databases and found a chickenpox-related hospitalisation rate of 3.56/100,000 person-years, a consultation rate of 20.1/100,000 person-years in specialist care and 109/100,000 person-years in primary care in Sweden in 2007-2013. In Study II, we included patients hospitalised with chickenpox in Stockholm and Gothenburg in 2012-2014. Their median age was 3.6 years. 43.1% of children and 67.4% of adults had an underlying condition. Overall 87.2% and 63.0% developed complications, respectively. There was no increased risk of complications among those with underlying conditions. In addition, in a nation-wide serology study using residual samples from 2011-2013, we found a VZV seroprevalence of 66.7% in 5-year-olds and 91.5% in 12-year-olds. In Study III, we compared demographic and socio-economic factors for children hospitalised with chickenpox, influenza and respiratory syncytial virus with patients with rotavirus, in a paediatric hospital in Stockholm in 2009-2014. We found that admitted chickenpox cases were older and lived in a household with more children than the cases with rotavirus. In Study IV, we explored the impact of chickenpox vaccination on shingles incidence in a mathematical model under a range of assumptions regarding VZV immunity after an encounter with a contagious case, so-called exogenous boosting (EB). We found that EB could be strong, intermediate or weak and still not cause a surge in shingles incidence after chickenpox vaccination. In addition, the same transmission model was used to investigate the impact of various strategies for vaccination against chickenpox and/or shingles in Sweden. In conclusion, a majority of Swedes had chickenpox in early childhood. The need for hospitalisation was low. More than half of complications were seen in previously healthy patients. Chickenpox vaccination led to a dramatic decrease in chickenpox incidence in our model, whereas the impact on shingles incidence was dependent on the assumed strength and duration of exogenous boosting. Of the assessed vaccination strategies, two-dose chickenpox vaccination in early childhood combined with shingles vaccination (RZV) at 65 years prevented the most VZV cases in the model. However, a cost-effectiveness analysis is needed to evaluate which vaccination strategy has the most reasonable costs for healthcare and society in relation to its health effects

The burden of chickenpox disease in Sweden

Abstract Background Chickenpox vaccine is not included in the routine childhood vaccination programme in Sweden. The aim of this study was to estimate the baseline of national chickenpox disease burden, as comprehensive studies, required for an assessment regarding vaccine introduction, are lacking. Methods We used available health care registers and databases; the death register, hospitalisations register, communicable disease notifications database, Stockholm County registers on consultations in specialist and primary care, temporary parental benefit to care for a sick child, and searches on the health care system’s website. From each data source, records regarding chickenpox were identified and extracted, either using relevant diagnosis codes (ICD-10) or key words. A descriptive analysis with regards to number of cases and incidence, severity, and seasonality, was carried out covering the time period 2007 to 2013. Results There were on average 333 patients hospitalised annually due to chickenpox, yielding a hospitalisation rate of 3.56/100,000 person-years. We found a slight male predominance in hospitalised cases. The highest hospitalisation rate was seen in 1 year-olds, whereas the peak in primary care consultations was in 2 year-olds. Nearly a quarter of children had parents who reported absence from work to care for them when sick with chickenpox. The average yearly death rate from chickenpox was 0.034/100,000 person-years. The duration of hospital stay increased with age. The seasonality in number of searches on the health care website corresponded well with hospitalisations and primary care consultations with peaks in spring. Conclusions This study shows chickenpox death and hospitalisation rates in range with other European countries without routine vaccination. Swedish children fall ill with chickenpox at a very young age. The study provides essential input for future discussions on the introduction of routine chickenpox vaccination in Sweden

Cost-effectiveness of varicella and herpes zoster vaccination in Sweden : An economic evaluation using a dynamic transmission model

Objectives Comprehensive cost-effectiveness analyses of introducing varicella and/or herpes zoster vaccination in the Swedish national vaccination programme. Design Cost-effectiveness analyses based on epidemiological results from a specifically developed transmission model. Setting National vaccination programme in Sweden, over an 85- or 20-year time horizon depending on the vaccination strategy. Participants Hypothetical cohorts of people aged 12 months and 65-years at baseline. Interventions Four alternative vaccination strategies; 1, not to vaccinate; 2, varicella vaccination with one dose of the live attenuated vaccine at age 12 months and a second dose at age 18 months; 3, herpes zoster vaccination with one dose of the live attenuated vaccine at 65 years of age; and 4, both vaccine against varicella and herpes zoster with the before-mentioned strategies. Main outcome measures Accumulated cost and quality-adjusted life years (QALY) for each strategy, and incremental cost-effectiveness ratios (ICER). Results It would be cost-effective to vaccinate against varicella (dominant), but not to vaccinate against herpes zoster (ICER of EUR 200,000), assuming a cost-effectiveness threshold of EUR 50,000 per QALY. The incremental analysis between varicella vaccination only and the combined programme results in a cost per gained QALY of almost EUR 1.6 million. Conclusions The results from this study are central components for policy-relevant decision-making, and suggest that it was cost-effective to introduce varicella vaccination in Sweden, whereas herpes zoster vaccination with the live attenuated vaccine for the elderly was not cost-effective–the health effects of the latter vaccination cannot be considered reasonable in relation to its costs. Future observational and surveillance studies are needed to make reasonable predictions on how boosting affects the herpes zoster incidence in the population, and thus the cost-effectiveness of a vaccination programme against varicella. Also, the link between herpes zoster and sequelae need to be studied in more detail to include it suitably in health economic evaluations

Large outbreak of cryptosporidium hominis infection transmitted through the public water supply, Sweden

In November 2010, approximate to 27,000 (approximate to 45%) inhabitants of Östersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized by a rapid onset and high attack rate, especially among young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily, and gluten intolerance were identified as risk factors for acquiring cryptosporidiosis. Also, chronic intestinal disease and young age were significantly associated with prolonged diarrhea. Identification of Ctyptosporidium hominis subtype lbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens

Risk of HIV transmission from patients on antiretroviral therapy: A position statement from the Public Health Agency of Sweden and the Swedish Reference Group for Antiviral Therapy

The modern medical treatment of HIV with antiretroviral therapy (ART) has drastically reduced the morbidity and mortality in patients infected with this virus. ART has also been shown to reduce the transmission risk from individual patients as well as the spread of the infection at the population level. This position statement from the Public Health Agency of Sweden and the Swedish Reference Group for Antiviral Therapy is based on a workshop organized in the fall of 2012. It summarizes the latest research and knowledge on the risk of HIV transmission from patients on ART, with a focus on the risk of sexual transmission. The risk of transmission via shared injection equipment among intravenous drug users is also examined, as is the risk of mother-to-child transmission. Based on current knowledge, the risk of transmission through vaginal or anal intercourse involving the use of a condom has been judged to be minimal, provided that the person infected with HIV fulfils the criteria for effective ART. This probably also applies to unprotected intercourse, provided that no other sexually transmitted infections are present, although it is not currently possible to fully support this conclusion with direct scientific evidence. ART is judged to markedly reduce the risk of blood-borne transmission between people who share injection equipment. Finally, the risk of transmission from mother to child is very low, provided that ART is started well in advance of delivery