we quantified the results of entry screening for influenza a(h1n1)pdm09 at auckland international airport . using the information generated during screening , we retrospectively estimated the number of infected travelers who actually passed through the airport . to estimate the sensitivity of screening ,
we then compared screening findings with the expected number of infected travelers who passed through the airport .
ethical approval was received from the northern x regional ethics committee of the new zealand ministry of health .
the numbers of crew members on inbound international aircraft were estimated by using averages for flights into auckland .
the number of travelers detected at each step and referred to the next step of the screening process was obtained from auckland regional public health service records .
a confirmed case was one that met the current case definition ( as published on the ministry of health website , www.health.govt.nz ) and one for which rt - pcr result was positive .
we estimated the number of infected travelers screened as the total number of confirmed cases in new zealand during this period , multiplied by the proportion of overseas - acquired cases , and the proportion of international travelers arriving at the airport .
on april 30 , 2009 , nonseasonal influenza a ( h1n1 ) was made notifiable , and these data were collated on the national surveillance database ( episurv ) ( www.surv.esr.cri.nz/episurv ) .
the proportion of infected travelers who acquired the infection overseas was extrapolated from ministry of health records of the first 100 cases of pandemic ( h1n1 ) 2009 because this information was not collected for all travelers with confirmed infection .
the proportion of travelers who passed through the airport was determined from statistics new zealand ( www.stats.govt.nz ) arrivals records .
confidence intervals were calculated by using the online calculator for screening on open epi ( 4 ) . during the screening period , 456,518 international travelers were screened ; 406 ( 0.09% ) of these were referred for medical assessment . of those ,
rt - pcr results were located for 89 ( 82% ) , among which 4 were positive .
the expected number of infected travelers estimated to have passed through the border during the screening program was therefore 69 , giving an estimated sensitivity of 5.8% ( 95% ci 2.3%14.0% ) .
this form of border screening is therefore unlikely to have substantially delayed spread of the pandemic into new zealand in 2009
. limitations of influenza screening include the high proportion of asymptomatic infected travelers ( 5 ) , incubation of infections acquired before or during a flight ( 3 ) , reliance on self - identification , limitations of case definitions , and limitations of thermal scanning ( 6 ) . modeling data have shown that the ability of border screening to delay global pandemic influenza is closely linked to the effectiveness of the screening process or travel restriction used . to delay influenza spread by 1.5 weeks , border restrictions need to reduce imported infections by 90% ( 7 ) .
the potential effectiveness of screening arriving travelers to prevent or delay influenza epidemics has been debated .
mathematical models and literature reviews have argued for ( 7,8 ) and against ( 911 ) this approach .
some authors have found that entry screening for respiratory conditions or influenza a(h1n1)pdm09 is insensitive and not cost - effective ( 12 ) .
this study has several limitations , particularly with regard to estimating the number of infected travelers who would have passed through the airport during the screening period .
most cases of illness acquired overseas would probably not have been notified , particularly those in patients with mild illness who did not see a doctor or who saw a doctor but did not receive a diagnosis .
the estimated proportion of overseas - acquired cases was based on data from the first 100 cases and would have decreased as the pandemic progressed .
the net effect of these factors is unknown , but they would probably have increased the estimated number of undetected infected travelers passing through screening , thereby further reducing the estimated sensitivity of screening .
it might provide public assurance and confidence that something is being done ( 14 ) .
the communication of health information and advice on how to seek treatment is consistently recommended as a pandemic prevention strategy ( 12,15 ) and is usually delivered as part of border screening programs .
these benefits need to be balanced against the considerable resources used , opportunity cost ( resources used for this activity and thereby unavailable for other activities ) , uncertain effectiveness , and inconvenience of border screening .
to delay or prevent influenza entry at borders , influenza screening needs to be considerably more effective than the mostly passive program described here .
we hope that during this interepidemic period , a major international review of the role of international air travel in the dissemination of emerging infectious diseases will be conducted to identify effective interventions .
such a review should consider systemwide approaches , including exit screening , standardized health declarations , active screening of individual passengers ( including use of rapid laboratory tests and thermal scanning ) , passenger tracking , policies and practices that support sick travelers wishing to defer travel , and circumstances where airline travel should be suspended entirely .
 entry screening for influenza a(h1n1)pdm09 at auckland international airport , new zealand , detected 4 cases , which were later confirmed , among 456,518 passengers arriving april 27june 22 , 2009 . 
 on the basis of national influenza surveillance data , which suggest that 69 infected travelers passed through the airport , sensitivity for screening was only 5.8% . 