Melese M, Wolde F, Sori T, Girma S. Role of Understanding the Chain of Infection for Effective Infectious Disease Prevention and Control

Melese M; Wolde F; Sori T; Girma S

Review Article

Austin J Public Health Epidemiol. 2025; 12(2): 1178.

Role of Understanding the Chain of Infection for Effective Infectious Disease Prevention and Control

Melese M¹*, Wolde F¹, Sori T¹ and Girma S²

¹Addis Ababa University, College of Veterinary Medicine and Agriculture, Bishoftu, Ethiopia

²Masha Livestock and fishery, South West, Ethiopia

*Corresponding author: Melkamu Melese, Addis Ababa University, College of Veterinary Medicine and Agriculture, Bishoftu, Ethiopia Email: melkamu.gsr-3632-17@aau.edu.et / mmelese61@gmail.com

Received: June 15, 2025 Accepted: July 18, 2025 Published: July 21, 2025

Summary

Understanding the Chain of Infection is fundamental to preventing and controlling infectious diseases. This conceptual framework outlines six interconnected components essential for disease transmission: infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host. Breaking one or more links in this chain can effectively interrupt disease spread. Strategies include accurate diagnosis, improved sanitation, vaccination, hand hygiene, and vector control, among others. This model finds practical use in both public health and clinical settings. Public health efforts prioritize activities such as disease monitoring, community education, policy implementation, and improving environmental conditions, while clinical practices concentrate on preventing infections, isolating patients, and implementing vaccination strategies. However, its effectiveness is often constrained by obstacles like antimicrobial resistance, socio-economic challenges, environmental shifts, and inadequacies in healthcare infrastructure. Embracing a One Health approach, which unifies human, animal, and environmental health, enhances this framework by tackling zoonotic disease threats and common environmental factors. Future strategies for managing infectious diseases involve innovations in diagnostic tools, leveraging artificial intelligence for outbreak forecasting, developing new vaccines, and fostering international cooperation. The Chain of Infection model provides a systematic and adaptable tool for addressing both localized outbreaks and global health challenges. By leveraging interdisciplinary collaboration and innovative strategies, it offers a robust pathway to enhance global health resilience in the face of evolving threats.

Keywords: Chain of infection; Epidemiology; Disease Transmission; One Health Approach

Abbreviations

CDC: Center of disease Control; WHO: World health Organization; IPC: Infection Prevention and Control; AMR: Antimicrobial Resistance.

Introduction to the Chain of Infection

Infection is the invasion and multiplication of microorganisms, such as bacteria, viruses, fungi, or parasites, within a host's body. These microorganisms may be harmless, beneficial, or pathogenic (disease-causing). Infection occurs when the body’s immune system is unable to control the invading pathogens, leading to damage to the host's tissues and subsequent illness [1].

The Chain of Infection is a conceptual model that describes the process by which infectious diseases are transmitted and spread. It highlights six interconnected components that must be present and aligned for an infection to occur: the infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host. Each link in the chain represents a step in the transmission process, and understanding this sequence is fundamental to developing strategies to prevent and control infectious diseases effectively [2]. By targeting one or more links in the chain, public health professionals can interrupt the transmission of pathogens, reducing the spread of disease. For example, measures such as vaccination, hand hygiene, environmental sanitation, and antimicrobial use are based on breaking specific links in the chain of infection. This framework is widely used in infection control programs, including in healthcare settings and community health initiatives.

Components of the Chain of Infection

The chain of infection consists of six interconnected components, each representing a critical step in the transmission of infectious diseases (Figure 1).

Figure 1: Chain of infection. Source: https://www.nipcm.scot.nhs.uk/media/1579/care_homes_chain_of_infection_graphic.jpg

    
    
    Figure 1: Chain of infection.
Source: https://www.nipcm.scot.nhs.uk/media/1579/care_homes_chain_of_infection_graphic.jpg

Importance of Understanding the Chain of Infection

Understanding the chain of infection is paramount because it provides a systematic framework for developing targeted interventions. By identifying and breaking any single link in the chain, the transmission of the infectious agent can be interrupted, preventing disease. This model moves beyond simply treating the sick individual to addressing the broader context of disease spread.

Strategies to Break Each Link in the Chain

Controlling the Infectious Agnt:

• Strategies: Rapid and accurate diagnosis, prompt treatment with appropriate antimicrobials (where applicable), proper use of disinfectants.

• Relevance to document: Access to quality healthcare and effective treatment are crucial for reducing disease burden, especially in urban settings [3,4].

Eliminating the Reservoir:

• Strategies: Sanitation and hygiene improvements, proper waste management, safe food and water practices, animal vaccination programs, isolation of infected individuals.

• Relevance to document: Good water quality and access to sanitation are critical challenges in urban areas, and contaminated water contributes to infectious disease transmission [5,6]. Innovative waste management programs (e.g., Curitiba's "Garbage Purchase" initiative; Branas et al., [7]) and plastic bans [8] improve sanitation. Kigali's efforts reduced waterborne disease incidence [9].

Blocking Portals of Exit and Entry:

Strategies: Hand hygiene (handwashing, hand sanitizers), personal protective equipment (PPE) like masks, gloves, and gowns, proper food handling, safe injection practices, wound care.

Relevance to document: Improved ventilation in housing can reduce the spread of respiratory infections [4], linking built environment design to preventing pathogen exit.

Interrupting Mode of Transmission:

• Strategies: Physical distancing (social distancing), proper ventilation, isolation of infected individuals, vector control (e.g., mosquito nets, insecticides), safe injection practices, proper food preparation and storage.

• Relevance to document: High-density living and public transportation were highlighted as transmission facilitators during COVID-19 without adequate protective measures [10,11]. Improving urban design for safe access to necessities [12] and effective ventilation [13] are indirect but important strategies. Vector-borne diseases are a significant challenge in urban environments, emphasizing the need for vector control [14,15].

Protecting the Susceptible Host:

• Strategies: Vaccination, improved nutrition, adequate rest, stress reduction, access to safe housing, and overall strengthening of the immune system.

• Relevance to document: Addressing food insecurity [16] and upgrading informal settlements [17] directly contribute to host resilience by improving living conditions and access to resources, making individuals less susceptible.

Applications in Public Health and Clinical Practice

The concept of the chain of infection is extensively applied in public health and clinical practice to design effective strategies for preventing and controlling infectious diseases. By identifying and targeting specific links in the chain, professionals can mitigate the risk of disease transmission [18].

In Public Healt

• Disease Surveillance and Outbreak Response: Monitoring and identifying outbreaks to target interventions, such as isolating infectious individuals or vaccinating at-risk populations.

• Community Education: Promoting hygiene practices like hand washing to interrupt transmission.

• Policy Implementation: Enforcing food safety regulations to prevent gastrointestinal infections or vector control programs to combat diseases like malaria.

• Environmental Interventions: Ensuring safe water, sanitation, and vector control to interrupt transmission

In Clinical Practice

• Infection Prevention and Control (IPC) in Healthcare: Adopting standard precautions, such as hand hygiene and sterilization of medical equipment, to block modes of transmission.

• Vaccination Programs: Strengthening host defenses by immunizing against preventable diseases.

• Patient Isolation: Minimizing contact between infected patients and others to break the chain of transmission.

• These applications are critical in addressing emerging infectious diseases and antimicrobial resistance, emphasizing the importance of a coordinated approach in public health and clinical settings.

Challenges in Breaking the Chain of Infection

Efforts to interrupt the chain of infection face numerous challenges that can hinder the effectiveness of disease prevention and control measures. These challenges arise from biological, environmental, social, and systemic factors:

Antimicrobial Resistance (AMR): The emergence of drugresistant pathogens limits the effectiveness of treatments, making it harder to eliminate the infectious agent [19,20].

Example: Multidrug-resistant Mycobacterium tuberculosis in tuberculosis control.

Socioeconomic and Cultural Barriers: Poverty, lack of education, and cultural practices can impede access to healthcare, vaccines, and sanitation [21].

Example: Vaccine hesitancy driven by misinformation in some communities.

Environmental Changes and Zoonotic Diseases: Deforestation, urbanization, and climate change increase human-animal interactions, facilitating zoonotic disease transmission [22].

Example: Emerging diseases like COVID-19 linked to wildlife reservoirs.

Globalization and Travel: Rapid movement of people and goods enables the spread of infectious diseases across borders [23].

Example: The rapid global spread of SARS-CoV-2 during the COVID-19 pandemic.

Weak Healthcare Systems: Inadequate infrastructure, insufficient funding, and lack of trained personnel undermine infection control efforts [24].

Example: Struggles in Ebola outbreak response in West Africa (2014–2016).

Behavioral and Policy Gaps: Failure to implement or adhere to effective policies and guidelines [25].

Example: Non-compliance with hand hygiene in healthcare settings.

Addressing these challenges requires integrated efforts, including strengthening healthcare systems, advancing research, and fostering community engagement.

Case Studies

Case Studies on Understanding the Chain of Infection

Many case studies highlight the practical applications of understanding the chain of infection in diverse public health contexts (Table 1).

Table 1: Case studies on understanding the chain of infection.

    
    
    Table 1: Case studies on understanding the chain of infection.

The Chain of Infection as a One Health Concept

The Chain of Infection model is particularly powerful when viewed through the lens of the One Health concept. One Health recognizes that human, animal, and environmental health are inextricably linked. This interconnectedness means that breaking the chain of infection effectively often requires understanding and intervening at the interfaces of these three domains.

Infectious Agent: The statistic that "approximately 60% of human pathogens are zoonotic in origin" directly links the infectious agent to the animal-human interface. Understanding this origin is crucial for early detection and control in both animal and human populations [26].

Reservoir: The reservoir for many pathogens often spans across species and environments. Animals can be reservoirs for human diseases (e.g., poultry for Salmonella), humans can be reservoirs for animal diseases, and the environment (water, soil) can harbor pathogens affecting both. Effective One Health interventions involve identifying and managing these diverse reservoirs across all sectors [5,6].

Portal of Exit/Entry: Shared environments facilitate the movement of pathogens between humans, animals, and the environment. Poor sanitation, inadequate waste management, and contaminated water, as highlighted in the document, are prime examples of environmental factors that serve as critical portals of exit and entry for pathogens affecting both human and animal health in urban areas [8,9].

Mode of Transmission: Many significant infectious diseases are vector-borne (e.g., dengue, malaria), directly involving the animalenvironment- human interface [14,15]. Environmental factors like climate change and inadequate drainage create breeding grounds for vectors. Additionally, transmission through common vehicles like contaminated food and water underscores the need for integrated food safety and environmental health programs [16]. Urban design choices, such as high-density living and public transport use, impact droplet and airborne transmission, as seen during the COVID-19 pandemic [10,11].

Susceptible Host: The susceptibility of both human and animal hosts is influenced by environmental conditions and broader socio-economic factors. Addressing issues like food insecurity [16] and upgrading informal settlements [17] directly contributes to strengthening the resilience of human populations, making them less susceptible to infections. Similarly, animal health programs contribute to healthier animal populations, reducing their susceptibility and potential to transmit pathogens to humans.

yy In essence, a One Health approach to breaking the chain of infection meaIntegrated Surveillance: Monitoring pathogens and resistance across human, animal, and environmental samples.

yy Collaborative Intervention: Joint efforts between public health, veterinary, agriculture, and environmental sectors (Rüegg et al., 2018).

yy Holistic Policy: Developing policies that consider the health impacts across all sectors, from urban planning [27] and green infrastructure [28] to waste management and water quality.

Future Directions in Understanding the Chain of Infection

Despite significant advancements in understanding the chain of infection, several knowledge gaps persist. For instance, there is a need for further research on the effectiveness of various interventions at different points in the chain of infection across diverse healthcare settings. Advancements in science, technology, and global health strategies continue to refine the understanding and application of the chain of infection concept. By future directions, public health systems can improve their capacity to interrupt the chain of infection, ensuring better disease prevention and control in a rapidly changing world (Table 2).

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Citation: Melese M, Wolde F, Sori T, Girma S. Role of Understanding the Chain of Infection for Effective Infectious Disease Prevention and Control. Austin J Public Health Epidemiol. 2025; 12(2): 1179.

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