COVID-19 Transmission on International Flights Contributed to Disease Spread – Renal and Urology News

Evidence of COVID-19 transmission on international passenger flights was found via contact tracing, suggesting in-flight secondary transmission contributed to the spread of the virus. These study findings published in BMC Infectious Diseases.

Researchers conducted a retrospective cohort study using a large national contact tracing dataset to determine the occurrence and extent of SARS-CoV-2 transmission on international flights. They also aimed to identify risk factors associated with secondary transmission. The study included data from international flights arriving in England between August 2021 and October 2021. Transmission risk was estimated by calculating the secondary attack rate (SAR) across all flights and by individual flights.

The final analysis included 11,307 index infections across 7831 different flights, as well as 667,849 individual flight contacts.

Secondary transmission occurred among a total of 5289 flight contacts, indicating an overall SAR for in-flight COVID-19 transmission of 0.79% (95% CI, 0.77-0.81). The mean SAR per individual flight was 0.80%, (minimum, 0%; median, 0%; maximum, 25%). Genomic data were available for 2298 (26%) index infections and 763 (14%) secondary diagnoses. Of 173 infected individuals linked by flight exposure with available unique property reference numbers (UPRN), 26 (15%) shared genomic data without a matching UPRN, suggesting in-flight transmission without household contact.

Flight duration data were available for 63,677 (9.6%) flight contacts and 392 (7.4%) individuals who were infected via secondary transmission. There was a slight, but statistically insignificant, increase in the number of secondary diagnoses for flights longer than 2 hours (odds ratio [OR], 1.19; 95% CI, 0.97-1.46; P =.10). Individuals who sat within 2 rows of those with an index infection were more likely to be infected via secondary transmission, including those on flights with 3 × 4 × 3 (OR, 2.86; 95% CI, 2.29-3.56; P <.001) and 3 × 3 (OR, 1.82; 95% CI, 1.50-2.22; P <.001) seating arrangements.

The researchers noted that secondary transmission was significantly less common among vaccinated individuals (OR, 0.59; 95% CI, 0.54-0.65; P <.001). Compared with the youngest age group (range, 0-24 years), secondary transmission was significantly more common in individuals aged 40 to 64 years (OR, 1.39; 95% CI, 1.27-1.53; P <.001) and in those older than 65 (OR, 1.32; 95% CI, 1.18-1.48; P <.001).

Using 1 index infection as a reference, a higher number of index infections reported on an individual flight was associated with increased risk for secondary transmission:

• 2-3 index infections (OR, 1.29; 95% CI, 1.22-1.37; P <.001); and
• ≥4 index infections (OR, 2.53; 95% CI, 2.31-2.77; P <.001).

After adjusting for other independent predictors, a similar relationship was observed between number of symptomatic infections reported on an individual flight and secondary transmission risk:

• 1 symptomatic infection (adjusted OR, 1.16; 95% CI, 1.07-1.26; P <.001);
• 2-3 symptomatic infections (aOR, 1.22; 95% CI, 1.06-1.40; P =.004); and
• ≥4 symptomatic infections (aOR, 1.85; 95% CI, 1.40-2.44; P <.001).

The adjusted analysis also showed that the risk for secondary transmission was lower for fully vaccinated individuals (aOR, 0.52; 95% CI, 0.47-0.57; P <.001) and partially vaccinated individuals (aOR, 0.75; 95% CI, 0.63-0.89; P <.001).

The major limitation of this study is the context-specific nature of the analysis, as the dominant COVID-19 variant, vaccination prevalence, and enforcement of enhanced hygiene measures changed over time.

“The large absolute number of secondary cases observed during the study period indicate this may be an important route of transmission and public health interventions should be considered to help control this in future epidemics,” the researchers concluded.

This article originally appeared on Infectious Disease Advisor