The pathogen specific burden of hospitalisation for enteric and blood stream infection in children and young people in Western Australia

Parveen Fathima, Hannah C Moore, Thomas Snelling, Deborah Lehmann

Enteric infections cause significant mortality and morbidity worldwide, in both resource rich and poor settings. In WA, enteric infection is one of the leading causes for infection-related hospitalisations in children under the age of 2 years and Aboriginal infants are 8 times more likely to be admitted for enteric infections than non-Aboriginal infants. Although enteric infection is usually self-limiting in healthy children, it can lead to acute morbidity through dehydration and chronic morbidity through failure to thrive and under-nutrition. Furthermore, some enteric pathogens can translocate into the normally sterile bloodstream causing bloodstream infection (BSI) and sepsis.

The causative pathogens of enteric infection are geographically, seasonally and temporally variable. Rotavirus infection has been the single most important cause of enteric disease in WA as with elsewhere in Australia and globally, but bacterial enteric infection due to Campylobacter spp., Salmonella spp., Shigella spp. and parasites are also frequently reported in infants in the Northern Territory, and those aged less than 5 years in remote WA, especially in Aboriginal infants.

Rotavirus vaccination commenced in WA in mid-2007 and has been accompanied by a reduction in rotavirus-specific and all-cause gastroenteritis hospitalisations. We hypothesise that rotavirus immunisation has not only had a direct impact on rotavirus gastroenteritis, but it also has an indirect impact on non-rotavirus enteric pathogens by reducing their transmission.

There are a number of observations arising from the field trial and post licensure experience with rotavirus vaccines which support this hypothesis and yet it has never been formally tested. These observations include the disproportionate impact of vaccination observed against severe diarrhoea and diarrhoea-related mortality. Because of its capacity to directly link hospitalisation with pathogen-specific pathology data, WA is in a unique position to address this hypothesis. The results are highly significant for understanding the overall impact of rotavirus vaccination, especially among Aboriginal children and in resource-poor settings where non-rotavirus pathogens account for a significant proportion of the total diarrhoeal disease burden.

Accurate data on causative pathogens for community-acquired enteric infection are needed to guide medical management and further public health interventions. Pathogen data relevant to WA are limited. WA is climatically diverse, and has a large remote Aboriginal population among whom enteric disease causing pathogens differ from those in the non-Aboriginal population. A recent study has shown diverging temporal trends in gastroenteritis hospitalisation rates in Aboriginal and non-Aboriginal children in the different geographical regions of WA. We need to study the changes, if any, in the prevailing enteric pathogens over time to determine if they are driving these trends.

In this project, we propose to investigate the pathogen-specific burden of community-acquired enteric and bloodstream infection in Aboriginal and non-Aboriginal populations, focusing on children presenting to Emergency Department facilities or being hospitalised across the state of Western Australia. The results will allow us to evaluate the overall impact of WA’s rotavirus vaccination program and will inform future preventive and management strategies.

Specific aims of this project are:

1. To characterise the epidemiology and pathogen- specific burden of disease for community-acquired enteric disease including enteric bloodstream infection among Western Australian (WA) children.
2. To describe the changes over time in the prevalent enteric pathogens causing presentations for diarrhoea and blood stream infection (BSI), and to compare overall and pathogen-specific rates of infection pre and post rotavirus vaccine introduction, using non-enteric BSI (Staphylococcus, Pneumococcus and Group A Streptococcus) as a control outcome.
3. To determine the demographic and clinical risk factors for community-acquired infection with enteric pathogens in WA.
4. To determine the reduction in emergency presentations and hospitalisations attributable to the rotavirus vaccine program.
5. To prioritise future public health interventions to address the residual burden of enteric diseases in WA.

So far we have identified 15,888 gastroenteritis coded hospital admissions among a cohort of 13, 881 children born between January 2000 and June 2014. The overall gastroenteritis hospitalisation rate was 4.6/1000 child-years for non-Aboriginal children and 21.5/1000 child-years for Aboriginal children. Increasing maternal age decreased the risk of gastroenteritis hospitalisation in non-Aboriginal children.

The risk of hospitalisation for gastroenteritis decreased with increasing levels of socio-economic advantage in non-Aboriginal children, with children in the most disadvantaged group having 1.5 times the risk as compared to children in the most advantaged group. There was no evidence of risk difference based on socio-economic disparity in Aboriginal children.

Plain Language summary: Enteric (gut) infections are a major cause of illness in children and young adults. Aboriginal children suffer from more gut infections compared with non-Aboriginal children. In addition to dehydration, severe gut infections can give rise to bloodstream infections (BSI) and other nutrition/growth related health problems.

By bringing together the birth, hospitalisation, and laboratory records of children across Western Australia over the last 10 years, we will investigate which pathogens (bacteria, viruses or parasites) are responsible for enteric infection related health care presentations in children, who are most at risk and what factors (such as age, region of residence, infant low birth weight, maternal age etc.) predicts the severity of illness.

We will assess the overall impact of the rotavirus vaccination program introduced for children in Western Australia in 2007. This will help us to better target further prevention and management strategies for these infections.

Funder: Princess Margaret Hospital Foundation New Investigator Project Grant 2013

External collaborator: Thomas Riley (UWA)