DARM DA study exercise group 3

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Introduction

Since travel restriction for an indetermined period of time is an unrealistic measure, more feasible tools to control the spreading of the swine flu to Finland are needed. We propose the use of thermal-image scanners combined with a PCR flu test.

The symptoms of swine flu are similar to regular flu symptoms. The most common symptoms include a sudden fever, a sore throat, cough and a runny nose. The incubation period for influenza (the time between infection and appearance of symptoms) is usually 2–3 days, but symptoms may start 1–7 days from contamination. Because the fever is one of the most common symtoms of swine flu, the idea is using the thermal-image scanners to prevent swine spreding with passangers incoming to Finland. The scanners could be set up at airports and other border control points for checking all incoming travellers. Thermal scanning is a quick and non-intrusive system for mass screening of people from a distance of more than one metre. The scanners use thermal imaging to assess the skin temperatures of people as they pass through a checkpoint, and transform that data into a coloured image on a screen. The scanners will be set up so that when someone with raised body temperature or the set threshold temperature of scanner (normally above 38(?)C), passes through the testing area, his/hers features will be highlighted in a particular colour. Those who are monitoring the screen of scenner would then pull over the persons with higer body temperature for further investigation and checking whether the observed higher body temperature is really because of a fever.

After the checking and confirming of the fever, person will be quarantined, because the laboratory tests are required to confirm whether a person has been infected with influenza A(H1N1)virus. There are several methods for testing swine flue, but use of PCR-test (real-time reverse transcriptase-polymerase chain reaction, rRT-PCR) is recommended for confirmation of novel cases, because PCR-test is recognized to be one of the most effective and sensitive tests (http://www.cdc.gov/h1n1flu/specimencollection.htm). PCR-test uses a device to amplify copies of genes so researchers can easily compare a sample taken from a sick person to the genetic material of the potentially pandemic infection. Running of PCR-test in laboratory takes few days (48-96 hours: http://www.cdc.gov/h1n1flu/guidance/diagnostic_tests.htm) and during that time person who is tested will be quarantied. Although the accuracy of PCR-test is quite good: hihg sensitivity 86-100% (http://www.cdc.gov/h1n1flu/guidance/diagnostic_tests.htm) and specificity ???(), the test can also provide "false negative" and "false positive" results. "False negative" is in cases where the person actually has the virus and the a negative result does not, by itself, exclude the possibility of swine flu virus infection. Another problem is that a positive result only indicates that the patient is presumptively infected with swine flu virus, but not the stage of infection.

When the positive swine flu case is detected, the patient will be hospitalized and the treatment with drugs will be started. The antiviral drugs can make the illness milder and make the patient feel better faster. They may also prevent serious flu complications. Beside antivirals, supportive care in hospital, focuses on controlling fevers, relieving pain and maintaining fluid balance, as well as identifying and treating any secondary infections or other medical problems.

Purpose

The question to be answered by this assessment is: can the use of thermal scanners combined with PCR tests prevent the spreading of swine flu to Finland if all passagers arriving to Finland will be scanner at the border control points?

Scope

This assessment is carried out to find out whether the installation of thermal scanners (and performance of PCR flu tests if fever is detected) to the Finnish airports, harbours and other border controls is a relevant system to prevent the swine flu spreading to Finland.

The purpose of this assessment is to find out if the thermal scanners could be used for preventing the spreding of swine flu to Finland.

Boundaries

Our assessment takes place in the moment (end of April 2009) when swine flu was starting to spread from Mexico, but no cases had yet been detected in Finland. At that time, The Finnish Ministry of Foreign Affairs was not issued any travel restrictions to the affected areas. The scanners would be placed in the Finnish airports, harbours and other border control points and all the passengers arriving to Finland abroad would be scanned. The scanning would be continued untill the decision about swine flu vaccination campaign in Finland will be made.

Scenarios

1. Scanners are used and the passangers with a raised body temperature (temp. above normal temperature 37±0.5 C) are tested for swine flu infection through the PCR test and quarantined/hospitalized if test is positive.

2. No scanners are used and the passangers can arrive to Finland freely without monitoring and controlling possible swine flu infection.

Intended users

The intended users of assessment will be:

The Finnish Ministry of Social Affairs and Health

The Finnish Ministry of Foreign Affairs

The Finnish Ministry of Transport and Communications

The Finnish Customs

Participants

The participants doing this assessments are: Bate Shadrak, Carmen Gil, and Minna Ruokolainen from the group 3 of Darm-course 2011

Definition

Causal diagram

Add a legend for you diagram.

Decision variables

Decision variable are

Use of thermal scanners combined with PCR test

No use of thermal scanners

Indicators

Passengers infected with influenza virus H1N1 get through the passenger control points on their arrival to Finland

Other variables

• Swine flu incubation takes 5 days on average (from 2 to 7 days)
• Symptoms last for ?? days on average
• Sensitivity and specificity of thermal scanner for fever
• Normal body temperature (37±0.5 C) of the population that follows a normal distribution
• Sensitivity of the PCR swine flu test: 80-100%
• Specificity of the PCR swine flu test: 99 %
• Number and origin of passengers travelling to Finland
• Prevalence of swine flu in different countries
• Intake of antipyretic drugs (e.g. painkillers)

Calculation

1. To estimate the fraction of arriving passengers that could be infected, we need to know the number of passengers per day, the origin and prevalence of swine flu in each country
2. To estimate the accuracy of thermal scanner determining if the passenger has fever or not, we need to know the sensitivity and specificity of the thermal scanners. The detectability of the fever is also dependent on the likelihood that passenger is using antipyretic drugs. We also need to take into account the incubation time for swine flu, because during this period infected people do not have fever. In this step we also need to know the prevalence of swine flu. It is needed to know the body temperature of population, which has a normal distribution.
3. To estimate accuracy of PCR-test in determining whether the fever is caused by swine flu or not, we need to know the sensitivity and specificity of the PCR-test.
4. The outcomes will be expressed as expected utilities. We will assign the utility 0 for swine flu and utility 1 for healthy.

Analyses

EXTRA
* Analyses: statistical and other analyses that contain two or more variables, e.g. optimizing.

Result

To make a final decision we should calculate the expected utilities of using thermal scanners combined with PCR-tests or not. To make the decision of using scanners we would need the expected utility to be very close to 1. Otherwise there would be too high probability of swine flu spreading to Finland and the scanners would be useless.