Airborne Transmission of SARS-CoV-2 Delta Variant within Tightly Monitored Isolation Facility, New Zealand (Aotearoa)

Abstract

In New Zealand, international arrivals are quarantined and undergo severe acute respiratory syndrome coronavirus 2 screening; those who test positive are transferred to a managed isolation facility (MIF). Solo traveler A and person E from a 5-person travel group (BCDEF) tested positive. After transfer to the MIF, person A and group BCDEF occupied rooms >2 meters apart across a corridor. Persons B, C, and D subsequently tested positive; viral sequences matched A and were distinct from E. The MIF was the only shared location of persons A and B, C, and D, and they had no direct contact. Security camera footage revealed 4 brief episodes of simultaneous door opening during person A's infectious period. This public health investigation demonstrates transmission from A to B, C, and D while in the MIF, with airborne transmission the most plausible explanation. These findings are of global importance for coronavirus disease public health interventions and infection control practices.

Keywords: COVID-19; Delta variant; New Zealand; SARS-CoV-2; airborne transmission; coronavirus disease; respiratory infections; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Timeline of infectious periods, test results, and relative locations of persons A–F, implicated in airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant between separate nonadjacent rooms within a tightly monitored MIF, New Zealand. Colors indicate persons A–F; bars represent each person’s infectious period of 10 days after symptom onset or the first positive rRT-PCR test. Syringe symbol indicates person was fully vaccinated against coronavirus disease. Person A occupied room 277 and travel group BCDEF occupied adjoining rooms 276 and 278 on the opposite side of the corridor in block 2 of the MIF. The doors to the rooms were 2.135 m apart. Map-arrow symbols indicate country of origin (Philippines and United Arab Emirates); airplane symbols denote date of arrival in New Zealand. Episodes of simultaneous door-opening between room 277 and rooms 276/278, each lasting 3–5 seconds, are indicated with ↓1 to ↓4. Positive SARS-CoV-2 rRT-PCR test results are indicated by (+); negative rRT-PCR test results are indicated by (–). MIF, managed isolation facility; MQF, managed quarantine facility.

Figure 2

Layout of managed isolation facility block 2, New Zealand, in which airborne transmission of severe acute respiratory syndrome coronavirus 2 Delta variant occurred between separate nonadjacent rooms. Colored circles indicate persons A–F. Person A occupied room 277 and travel group BCDEF occupied adjoining rooms 276 and 278 on the opposite side of the corridor, 2.135 m apart. Red arrow indicates direction of probable airborne transmission of Delta variant from person A to persons B, C, and D. Blue arrows indicate direction of airflow.

Figure 3

Unrooted maximum-likelihood phylogenetic tree of genomes from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) isolated from persons A, B, C, D, and E, implicated in airborne transmission of SARS-CoV-2 Delta variant between separate nonadjacent rooms within a tightly monitored managed isolation facility, New Zealand, set among a background of other lineage B.1.617.2 (Delta variant) genomes sampled from around the world during July 1–14, 2021. Colored circles indicate persons A–E. Person F is not included because they were not infected with SARS-CoV-2 during the timeframe of this investigation. Upper left phylogenetic scale bar indicates number of nucleotide substitutions per site. Lower right scale shows number of mutations (single nucleotide polymorphisms) difference between viral sequences isolated from persons A, B, C, D, and E.

Figure 4

Possible mechanisms of airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant between separate nonadjacent rooms within a tightly monitored MIF, New Zealand. A) Air flow through rooms when room doors and external windows are closed; rooms are negative pressure and air moves from the corridor into the rooms, exiting by extractor fans. B) Movement of viral aerosols between rooms during episodes of simultaneous door-opening, when negative pressure generated by extractor fans is negated. C) Movement of viral aerosols under room doors, aided by opening of external room windows and outdoor meteorological conditions (wind speed and direction), which can create internal air flows within the building. Colored circles indicate persons A–F. Blue arrows indicate direction of air flow. Different types of infectious particles are annotated in red, with all infectious particles originating from person A. Red arrows indicate direction of movement of infectious particles. Person B is shown opening the door in this example; however, security camera footage could not identify which group member opened the door during the episodes. Security camera footage could not confirm that masks were worn by the persons answering the doors, but wearing of medical masks when opening doors is mandated in the MIF. MIF, managed isolation facility.