Infectious Disease Transmission Case Study: Tuberculosis and Airborne Spread
Scenario Overview
Figure 1.1 depicts a crowded hospital waiting room as an ideal setting for the spread of infectious diseases such as tuberculosis.
Pete: a prison inmate in California for 5 years who has contracted multidrug-resistant tuberculosis (MDR-TB).
After release, Pete visits relatives in Chicago and travels on a full flight, experiencing several severe coughing spasms during the journey.
Pete believes his coughing is routine given his active disease and years of experience with it.
After several days with relatives, Pete feels poorly and seeks treatment at a county hospital.
In the hospital waiting room, Pete is not bleeding or chest-pain symptomatic, so he is asked to sit and wait.
While waiting, Pete coughs again; he becomes a “one-man epidemic,” contagious, expelling Mycobacterium tuberculosis bacteria in an aerosol with each cough.
If droplets are small enough, they can travel a considerable distance and hang in the air for a relatively long period.
Pete’s travels expose a wide chain of contacts: everyone on the flight to Chicago; those travelers may have changed transportation and exposed others on their own routes; and Pete also exposes everyone in the hospital waiting room.
Pete brings a deadly pathogen into an environment where people are debilitated or immunocompromised, increasing the risk that newly infected individuals struggle to fight the pathogen.
Modern travel facilitates rapid dissemination of diseases; experts estimate some respiratory diseases could be moved around the world in less than t < 48 ext{ hours}.
A real-world parallel is SARS-CoV-2: after cases were identified in Wuhan at the end of 2019, it took just over t \approx 3 \text{ weeks} for cases to be reported in Europe once the World Health Organization became aware of the outbreak.
The scenario highlights how globalization and travel can accelerate the spread of infectious diseases.
Transmission Mechanisms
Transmission occurs via aerosols produced by coughing; when the person is contagious, each cough releases infectious bacteria.
Aerosolized bacteria are carried by air and can be inhaled by others in proximity or further away, depending on particle size and air currents.
Droplets that are small enough can travel beyond immediate contact and linger in the air, increasing the chance of inhalation by others nearby or in shared spaces.
The hospital environment can amplify transmission risk due to cluster exposure in waiting rooms and other crowded areas.
Host, Pathogen, and Environment Factors
Pete has active tuberculosis that is resistant to multiple drugs (MDR-TB), making treatment more complex and increasing public health concerns.
The environment in which transmission occurs includes crowded spaces (airports, planes, waiting rooms) where debilitated or immunocompromised individuals are present, increasing susceptibility to infection.
An immunocompromised host struggles to mount an effective immune response to new infections, heightening the impact of exposure to tuberculosis.
The concept of an “environment where people are debilitated from illness” heightens the risk of infection and clinical consequences from new exposures.
Exposure Timeline and Network Effects
Flight exposure: Pete potentially exposes every passenger on the flight to Chicago, expanding the immediate network of potential secondary cases.
Post-flight exposure: Some passengers may change transport or pass exposure to others along their travel routes, creating a chain reaction extending beyond the original flight.
Hospital exposure: Pete’s coughing in a crowded waiting room exposes all present, creating another node of potential transmission within a healthcare setting.
Cascading risk: The initial contagious event can lead to secondary cases among travelers and family members, who may further propagate the pathogen in their communities.
Rapid Travel and Global Spread
Modern travel enables rapid movement of pathogens across vast distances.
According to the text, some respiratory diseases could be moved around the world in less than t < 48 \,\text{hours}.
The SARS-CoV-2 example illustrates how quickly a pathogen can spread globally: it took just over t \approx 3 \,\text{weeks} for cases to be reported in Europe after initial awareness in Wuhan.
Chapter 8 (referenced in the transcript) discusses rapid travel and its implications for infectious disease spread.
Real-World Relevance and Implications
Globalization increases the speed at which diseases can travel from one region to another.
Crowded indoor environments (airports, planes, waiting rooms) are high-risk settings for respiratory pathogen transmission.
Early recognition, isolation, and public health interventions are critical to limiting the spread when a contagious individual is identified.
The example underscores the importance of infection control in healthcare facilities and the potential for healthcare settings to become amplification points for outbreaks.
Ethical, Practical, and Policy Implications
Balancing individual liberties (allowing travel and hospital access) with public health safety to prevent onward transmission.
The duty of healthcare systems to screen, isolate, and manage contagious patients to protect vulnerable populations.
Allocation of resources for rapid testing, contact tracing, and exposure management in crowded settings.
The need for global surveillance and rapid information sharing to respond to emerging infectious threats.
Key Terms and Concepts (from the transcript)
Mycobacterium tuberculosis: the bacterium responsible for tuberculosis.
Multidrug-resistant tuberculosis (MDR-TB): TB strain resistant to multiple standard treatments (as noted in Pete's case).
Aerosol: tiny droplets suspended in the air that can be inhaled.
Droplets: larger respiratory particles that may settle more quickly but can be inhaled if within close proximity.
Immunocompromised: a weakened immune system, increasing susceptibility to infections.
One-man epidemic: a single contagious individual who ignites a chain of transmission.
Rapid travel and global dissemination: the concept that modern travel can spread disease quickly across borders.
Chapter 8 reference: discussion of rapid travel and its implications (in the transcript).
Numerical References and Formulas
Time to move around the world for some respiratory diseases: t < 48 \,\text{hours}
SARS-CoV-2 spread example: initial awareness in Wuhan at the end of 2019; Europe cases reported after just over t \approx 3 \,\text{weeks}.