A surveillance study to evaluate the effectiveness of the Safe Travels Hawaii pre-travel testing program has found 45 COVID-19 cases out of 20,253 tests, or 2.2 per 1,000, over the past five weeks.

Preliminary surveillance data has revealed “a very strong risk for COVID-19 infection in returning residents relative to visitors,” according to a report by Dr. DeWolfe Miller, an epidemiologist from the University of Hawaii’s John A. Burns School of Medicine. But the study also shows that the initial testing is catching most of the infectious cases.

“The early results of this study show a small uptick in the number of travelers testing positive for COVID-19 upon receiving a second test after arrival,” Lt. Gov. Josh Green said in a news release, adding that he recommends all counties conduct a post-arrival antigen test followed by a PCR test for anyone testing positive for “extra assurance and an added layer of safety” in addition to pre-arrival testing.

The state’s pre-travel testing program allows travelers to bypass the mandatory 14-day quarantine if they get a negative test result 72 hours before their departure to the islands.

“Strategic post-testing for returning residents could also prove beneficial in slowing the spread of COVID-19,” Green said.

The surveillance study has drawn criticism from Honolulu Mayor Kirk Caldwell for leaning too heavily on Hawaii island data and falling short of its goal to randomly test 10% of arriving visitors four days after arrival. The bulk of the surveillance tests have come from Hawaii island and were provided as part of Mayor Harry Kim’s mandatory post-arrival test. Caldwell questioned the usefulness of the Hawaii island tests, which he said include people arriving from airports where they got a pre-test immediately prior to departure.

He cast doubt that the state’s surveillance program is accurately measuring the COVID-19 positivity rate of incoming travelers at a time when cases are soaring on the mainland, the origin for most of Hawaii’s visitors. Caldwell is expected to face off against Green in 2022 for the Democratic nomination for Hawaii governor.

The voluntary surveillance program, which found it difficult to recruit a sampling of participants, started on Oct. 19 following the pre-travel testing program that began on Oct. 15. Health officials reported this week that 13% of the state’s coronavirus cases were travel-related in November, up from 3% in October.

Meanwhile, health officials reported two coronavirus deaths and 108 new infections statewide, bringing the totals since the start of the pandemic to 235 fatalities and 17,501 cases. The two additional deaths were an Oahu man in his 70s and a Kauai man in his 80s, both of whom had underlying conditions. Kauai’s first on-island death had been earlier reported by county officials, but was added to the Department of Health’s death toll Wednesday. Nearly half — 46 of Oahu’s 93 new infections — are part of the recent cluster at the Waiawa Correctional Facility.

Miller, who is leading the surveillance program, has concluded initial data collection and will focus in the coming weeks on assessing the information for policymakers to determine the success of the state’s pre-travel testing program.

“We are very pleased with the surveillance study and it has extreme merit in assessing the Safe Travels Hawaii pre-travel testing program,” Green said. “We look forward to delivering a completed report to our state and county leadership so they can make data-based decisions on the best way to move the program forward and manage Hawaii’s COVID-19 response.”