U.S. airport entry screening in response to pandemic influenza: modeling and analysis

Abstract

Background: A stochastic discrete event simulation model was developed to assess the effectiveness of passenger screening for Pandemic Influenza (PI) at U.S. airport foreign entry.

Methods: International passengers arriving at 18 U.S. airports from Asia, Europe, South America, and Canada were assigned to one of three states: not infected, infected with PI, infected with other respiratory illness. Passengers passed through layered screening then exited the model. 80% screening effectiveness was assumed for symptomatic passengers; 6% asymptomatic passengers.

Results: In the first 100 days of a global pandemic, U.S. airport screening would evaluate over 17 M passengers with 800 K secondary screenings. 11,570 PI infected passengers (majority asymptomatic) would enter the U.S. undetected from all 18 airports. Foreign airport departure screening significantly decreased the false negative (infected/undetected) passengers. U.S. attack rates: no screening (26.9%-30.9%); screening (26.4%-30.6%); however airport screening results in 800 K-1.8 M less U.S. PI cases; 16 K-35 K less deaths (2% fatality rate). Antiviral medications for travel contact prophylaxis (10 contacts/PI passenger) were high - 8.8M. False positives from all 18 airports: 100-200/day.

Conclusions: Foreign shore exit screening greatly reduces numbers of PI infected passengers. U.S. airport screening identifies 50% infected individuals; efficacy is limited by the asymptomatic PI infected. Screening will not significantly delay arrival of PI via international air transport, but will reduce the rate of new US cases and subsequent deaths.

Figure 1

Probability of a passenger being infected with pandemic influenza Pip as a function of simulation day by region of origin.

Figure 2

Stochastic discrete event passenger process simulation.

Figure 3

Proposed U.S. airport international arriving passenger screening process.

Figure 4

Total number of passengers infected with pandemic influenza on inbound international flights for all 18 U.S. airports per day.

Figure 5

Number of passengers detected and actually infected with pandemic influenza – true positives (TP) – total for all 18 U.S. international airports per day.

Figure 6

Number of passengers infected with pandemic influenza that are not detected – false negatives (FN) – total for all 18 U.S. international airports per day.

Figure 7

Impact of international passenger airport screening on U.S. pandemic influenza cumulative incidence. Dashed curves – effect of 45-day entry delay with effective vaccine development.

Figure 8

Potential antiviral requirements initial 100 days – 18 U.S. International Airports.

Figure 9

Healthcare worker requirements for screening – 18 U.S International Airports.

Figure 10

Number of passengers who do not have pandemic influenza but erroneously diagnosed – False Positives (FPs) – total for all 18 U.S international airports per day.