(See Table 1, Table 2, Table 3.)
Table 1.
Assumptions and limitations of the Biggerstaff-Petersen and EUFRAT models
| Assumptions common to both models | Additional assumptions for the BP model | Additional assumptions for EUFRAT | |
|---|---|---|---|
| Assumptions related to reported case numbers | • Reported incident infections represent all symptomatic infections. | • Symptom onset dates for reported (symptomatic) cases are similar to asymptomatic infections. | |
| Assumptions related to blood donor characteristics | • Donation frequency is constant throughout the period of observation | • Donors have the same risk of infection as the general population. | |
| • All donors have the same risk of infection, which is constant, during the period of observation. | • Blood components from viremic blood donors transmit infection with 100% efficiency. | ||
| • Asymptomatic infection does not affect the donation behavior of donors. | • Donors with symptomatic infections either would not present to donate or would be excluded from donating. | ||
| • Likelihood of detection of infectious donors by the predonation questionnaire is constant throughout the infectious period. | |||
| Assumptions related to infection | • Historically estimated asymptomatic/symptomatic infection ratio and viremic periods are applicable to the study population and remain constant during period of observation. | • Risk from traveling donors is based on the duration of visit to outbreak/endemic area and time from departure to donating. | |
| • Relative timing and duration of viremia are independent of symptom onset time. | • Traveling donors have the same risk of infection as local inhabitants in outbreak/endemic area. | ||
| • Duration of viremia is the same for both symptomatic and asymptomatic cases. | • The proportion of donors that develop chronic infections is constant during period of observation. | ||
| Limitations | • Input parameters required for both models are often not well defined and contribute to the inherent uncertainty of the models. | • To perform the statistical resampling in the BP model, the dates of symptom onset for reported incident cases are required. | • A number of parameters in the EUFRAT model, including the difference in risk of infection between donors and the general population, the proportion of symptomatic cases in the general population that do not seek health care or are misdiagnosed, and the TT efficiency of infected end products and the level of immunity in the general population, are typically unknown for EID agents. |
| • The BP model does not take into account the reduction in TT risk related to efficiency of transmission by transfusion, pathogen reduction/inactivation due to blood processing and storage, and recipient immunity. |
Table 2.
Applications of the Biggerstaff-Petersen model for estimating transfusion-transmission risk
| Pathogen | Country (date of outbreak) | Formula/resamplinga | Comments | Reference |
|---|---|---|---|---|
| Chikungunya virus (CHIKV) | La Reunion Island (2005-2007) | Formula | • Proportion of asymptomatic infections based on local seroprevalence data | [83] |
| • Estimate of symptomatic cases accounts for cases who did not consult a GP. | ||||
| • Risk estimates did not take into account uncertainty of key parameters. | ||||
| • Estimates of CHIKV viremic periods based on DENV | ||||
| • Incidence based on clinical definition which may be an overestimate due to misdiagnosis of cases not due to CHIKV | ||||
| Dengue virus (DENV) | Australia (2004) | Formula | • Risk modeling used to monitor changes in risk over time | [82] |
| Dengue virus (DENV) | Australia (2008-2009) | Formula | • Mean donation frequency used to estimate number of infectious donations | [57] |
| • Estimated proportion of asymptomatic infections based on the seroprevalence data in outbreak area | ||||
| • Assumed donors who became symptomatic within a few days after donating would notify the blood service, and donation would be discarded | ||||
| Chikungunya virus (CHIKV) | Italy (2007) | Resampling | • Risk contribution for donors in the 2-d presymptomatic period was regarded as negligible and therefore excluded from modeling | [85] |
| Hepatitis A virus (HAV) | Latvia (2008) | Formula | • Model incorporated seroprevalence (immunity level) in general Latvian population | [86] |
| • Modeling restricted to individuals over 18 y (blood donor eligibility) | ||||
| • Accounted for ALT testing of donors and deferral if levels are high (>90 IU/L) | ||||
| • Did not take into account exclusion of donors who have a history of contact with HAV-infected individuals | ||||
| Chikungunya virus (CHIKV) | Thailand (2009) | Formula | • Modeled risk estimate of asymptomatic viremic donors was higher than indicated by donor screening. | [84] |
| Ross River virus (RRV) | Australia (2004) | Formula | • Duration of RRV viremia in humans based on mouse model | [87] |
| Ross River virus (RRV) | Australia (2013-14) | Formula | • Demonstrated changing risk levels geographically and over time | [88] |
| • Duration of RRV viremia in humans based on mouse model |
a
Refer to text for details.
Table 3.
Applications of the EUFRAT model
| Pathogen | Country (date of outbreak) | Comments | Reference |
|---|---|---|---|
| Chikungunya virus (CHIKV) | Italy (2007) | Applied both Biggerstaff-Petersen and EUFRAT models and calculations were performed: | [89] |
| • Using both weekly and average cumulative notified cases | |||
| • Using fixed input data and variable distribution values; estimated risk of asymptomatic viremic infection in donors was very similar by both methods. | |||
| Dengue virus (DENV) | Dutch donors returning form Suriname and Dutch Caribbean (2011-11) | Estimated the risk of traveling donors: | [91] |
| • Becoming infected while in outbreak area | |||
| • Transmitting infection to recipients upon return | |||
| Chikungunya virus (CHIKV), Coxiella burnetti (Q fever) | Italy (2007), Netherlands (2007-09) | Extension of EUFRAT. Modeled risk of infection: | [92] |
| • Prior to time of observation | |||
| • Potential risk subsequent to time of observation | |||
| C burnetti (Q fever) | Netherlands (2007-09) | • Risk modeling for an infection with acute and chronic phases | [93] |
| • Compared probability of donor being infected as estimated by EUFRAT and Biggerstaff-Petersen models | |||
| Ross River virus (RRV) | Australia (2013-14) | • Applied both EUFRAT and Biggerstaff-Petersen models | [88] |
| • Demonstrated temporal and geographical variations in risk. |
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