Defining an Outbreak in Aged Care

Infectious disease outbreaks pose a constant challenge in residential aged care facilities, affecting the health and well-being of vulnerable residents and placing a strain on staff and resources. While the economic impact of these events can be substantial, accurately predicting the costs and effectively managing outbreaks relies on a fundamental step: clearly defining what constitutes a case and an outbreak.

Developing an ideal case definition is vital to investigating an outbreak effectively. This definition should act as a benchmark, is standardised, and allows consistency in identifying the individuals considered part of the outbreak, both during an investigation and potentially across different outbreaks or locations. The infection may also be present in the community, which needs to be considered.

A strong case definition usually includes factors based on four key elements specific to the outbreak under investigation:

• Person: Describing shared characteristics of affected individuals, like age, sex, or occupation (e.g., residents living in a specific wing/corridor of an aged care facility).

• Place: Identifying the specific location of the facility associated with the outbreak.

• Time: Specifying a date for the onset of the infection to include relevant cases and exclude unrelated illnesses.

• Clinical Features: Initially, the investigation should be simple and objective (e.g., sudden onset of fever and cough); later, the infection definition is refined with laboratory results.
  
  

Case definitions can also be categorised by the certainty of identification into three categories (Suspected, Probable, Confirmed), and these categories are adjusted as more information becomes available. For example, a resident may present with an infection definition which could only be described as broad (e.g., resident in room 46 who has onset of fever and cough between January 4 and 6, 2025). This infection would later incorporate specific laboratory requirements and be correctly defined.

Beyond defining a specific outbreak, having standardised definitions for common infections in aged care settings is equally vital. These definitions provide clear criteria for identifying individual cases of common HAIs, which are a significant public health problem associated with increased morbidity, mortality, and cost.

Such definitions detail specific signs, symptoms, and often laboratory or diagnostic criteria for various infections frequently occurring in aged care, including:

• Urinary Tract Infections (UTIs): The definition of UTIs is based on symptoms such as acute dysuria, fever, or increased incontinence, combined with specific microbiological results from urine samples. Definitions exist and vary for residents with and without indwelling catheters.

•   Respiratory Tract Infections (RTIs): Definitions cover conditions from the Common cold and Influenza-like illness to more severe Pneumonia and Bronchitis, with criteria based on symptoms; fever, cough, and often results from chest X-rays or oxygen saturation.

• Skin and Soft Tissue Infections (SSTIs): Definitions for conditions like Cellulitis, Scabies, and Conjunctivitis, with criteria incorporating signs like redness, swelling, pus and lab confirmations to form a diagnosis.
  

• Gastrointestinal Tract Infections (GITIs): Including definitions for Gastroenteritis, Norovirus gastroenteritis, and Clostridium difficile infection, based on symptomatic criteria such as the frequency and nature of diarrhoea or vomiting, with laboratory confirmation of the specific pathogens or toxins.
  
  

These definitions often include specific thresholds for symptoms:

• Thresholds for symptoms - e.g., ≥ 3 liquid or watery stools within 24 h for diarrhoea

•  Clinical Markers - e.g., Leukocytosis defined as >14,000 WBC / mm3 or specific band counts

• Constitutional Criteria – fever, acute mental status

While sources providing these specific definitions, such as McGeer, don't provide details on the financial costs of an outbreak, they are foundational to assess accurate costings and effective resource allocation. Quantifying the full cost of outbreaks is a challenge, due in part to the scarcity of comprehensive cost data and the lack of standardised methods for predicting those costs. Economic evaluations often vary in their perspectives and how indirect costs are included in the data.

Consistent, criteria-based identification of infections and outbreaks, facilitated by these standardised definitions, is a necessary step towards establishing more precise financial benchmarks. Without clear and consistently applied definitions, tracking the true incidence and scope of outbreaks is difficult, leading to unreliable data on the resources consumed and costs incurred during these events.

For example, there is a significant economic burden of HAIs in New Zealand public hospitals. This is estimated at $955 million annually, calculated using a standardised methodology (ECDC) and relying on consistent HAI definitions for their prevalence survey. This demonstrates that reliable cost data is built upon reliable case identification.

Improved standardisation in defining infections and outbreaks would lead to more accurate and comparable cost data across aged care facilities and regions. This consistency is crucial for policymakers and providers to:

• Understand the true economic burden of different types of outbreaks.

• Identify the key cost drivers more precisely.
  

• Evaluate the cost-effectiveness of different prevention and control measures
  
• Allocate resources more effectively for preparedness and response.
  
  Essentially, you can't effectively cost what you can't consistently define and count. 

In conclusion, while the direct costs of an outbreak might be visible in staffing shortages, extra PPE use, and medical expenses, truly understanding and mitigating these costs begins with clear, standardised definitions. Having strong case definitions for specific outbreaks and standardised surveillance definitions for common infections like UTIs, RTIs, SSTIs, and GITIs is essential for effective surveillance and data collection. This consistency is not just about clinical management; it is necessary to develop the precise financial benchmarks needed to accurately assess the economic burden of infections in aged care. Prioritising the use of standardised definitions across Australasia would significantly enhance the accuracy and comparability of cost data, ultimately leading to better resource allocation, more informed policy decisions, and improved overall health outcomes for residents in aged care facilities.

This blog is the first of three examining the costs of an outbreak. The second will delve deeper into the McGeer criteria for identifying infection, and the third will consider the financial burden of outbreaks in aged care facilities in Australia and New Zealand.

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