Investigation of COVID-19 Outbreak among Wildland Firefighters

he Cameron Peak Fire in Colorado, USA, began

on August 13, 2020. Because of the magnitude

of this wildre, the response was coordinated by

various Incident Management Teams (IMT); wildre

responders included Colorado wildland reghter

crews as well as crews from around the country de-

ployed to Colorado for the response. On August 25,

2020, the Larimer County Department of Health and

Environment (LCDHE) and the Colorado Depart-

ment of Public Health and Environment (CDPHE) re-

ceived notication of a wildland reghter respond-

ing to the Cameron Peak Fire who tested positive for

SARS-CoV-2, the virus that causes COVID-19. This

reghter initially reported difculty breathing and

was transported to the local emergency department,

then released. The next day, he was admitted to the

hospital for continuing symptoms and tested posi-

tive for SARS-CoV-2 by reverse transcription PCR

(RT-PCR). LCDHE, in partnership with the IMT,

began contact tracing on the basis of the Centers for

Disease Control and Prevention (CDC) denition of

someone who was within 6 feet of an infected person

for a cumulative 15 minutes or more over a 24-hour

period (1). Two persons working on the same crew

and 5 additional responders at the camp were identi-

ed as close contacts and quarantined. During con-

tact interviews, it was reported that 2 crew members

of the index case-patient were experiencing cough

and headaches; both subsequently tested positive for

SARS-CoV-2. An outbreak was declared and reported

on September 2, 2020.

Wildre response personnel operating across the

state were in contact with CDPHE throughout the

wildre season regarding COVID-19 prevention and

response plans. In July 2020, before the Cameron Peak

Fire, CDPHE released public guidance documents ad-

dressing best practices for mitigating COVID-19 risks

at wildre camps (2). This document supplemented

best practice guidance available from other sources

Investigation of COVID-19

Outbreak among Wildland

Fireghters during Wildre

Response, Colorado, USA, 2020

Amanda Rei Metz, Matthew Bauer, Chelsey Epperly, Ginger Stringer,

Kristen E. Marshall, Lindsey Martin Webb, Molly Hetherington-Rauth, Shannon R. Matzinger,

Sarah Elizabeth Totten, Emily A. Travanty, Kristen M. Good, Alexis Burako

Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022 1551

Author aliations: Colorado Department of Public Health and

Environment, Denver, Colorado, USA (A.R. Metz, C. Epperly,

G. Stringer, K.E. Marshall, L.M. Webb, M. Hetherington-Rauth,

S.R. Matzinger, S.E. Totten, E.A. Travanty, K.M. Good,

A. Burako); Larimer County Department of Health and

Environment, Fort Collins, Colorado, USA (M. Bauer);

Centers for Disease Control and Prevention, Atlanta, Georgia,

USA (K.E. Marshall)

DOI: https://doi.org/10.3201/eid2808.220310

A COVID-19 outbreak occurred among Cameron Peak

Fire responders in Colorado, USA, during August 2020–

January 2021. The Cameron Peak Fire was the largest

recorded wildre in Colorado history, lasting August–De-

cember 2020. At least 6,123 responders were involved,

including 1,260 reghters in 63 crews who mobilized to

the re camps. A total of 79 COVID-19 cases were iden-

tied among responders, and 273 close contacts were

quarantined. State and local public health investigated

the outbreak and coordinated with wildre manage-

ment teams to prevent disease spread. We performed

whole-genome sequencing and applied social network

analysis to visualize clusters and transmission dynam-

ics. Phylogenetic analysis identied 8 lineages among

sequenced specimens, implying multiple introductions.

Social network analysis identied spread between and

within crews. Strategies such as implementing symptom

screening and testing of arriving responders, educating

responders about overlapping symptoms of smoke inha-

lation and COVID-19, improving physical distancing of

crews, and encouraging vaccinations are recommended.

SYNOPSIS

such as CDC (3), United States Forest Service (USFS)

(4), the Fire Management Board (5), and United States

Department of the Interior (6). At the time that the

Cameron Peak Fire started, a CDPHE occupational

health epidemiologist regularly attended a morning

safety brieng call organized by the USFS, in which

incident management team representatives from all

active res in Colorado called in with updates on

safety concerns including COVID-19.

Methods

Case Investigations

LCDHE and the Cameron Peak IMT collaborated to

conduct case investigations and contact tracing ac-

tivities. An outbreak case was dened as conrmed

or probable COVID-19 (determined using the Coun-

cil of State and Territorial Epidemiologists’ 2020 In-

terim COVID-19 Case Denition) (7) in a responder

who was onsite at the Cameron Peak Fire within 14

days of symptom onset or positive test. Close contacts

were identied on the basis of the CDC denition and

quarantined. CDPHE and local hospital laboratories

conducted SARS-CoV-2 RT-PCR testing using vari-

ous platforms.

Outbreak response consultation calls among

CDPHE, LCDHE, and IMT were held to provide

recommendations for isolation of cases, quaran-

tine of close contacts, and prevention practices such

as improving physical distancing. CDPHE’s Rapid

Response Team hosted a testing event for Cameron

Peak Fire responders before the rst positive case

was identied; surveillance and outbreak screen-

ing testing was offered to all Cameron Peak Fire re-

sponders starting August 24. Once the outbreak was

identied, widespread testing was conducted 11

more times during August 26–October 25, 2020. Af-

ter the re, the USFS conducted a Facilitated Learn-

ing Analysis to identify lessons learned from the

outbreak response (8).

Whole-Genome Sequencing

CDPHE performed tiled amplicon whole-genome se-

quencing (WGS) on 40 (51%) available specimens from

wildre responders (Appendix, https://wwwnc.

cdc.gov/EID/article/28/8/22-0310-App1.pdf);

the remainder of the specimens were unavailable

for sequencing because they were not sent to the

CDPHE laboratory. We assembled sequencing data

by using the Monroe workow and CDPHE’s publicly

available Nanopore data workow (https://github.

com/CDPHE).

Of the specimens available for WGS, 24 resulted in

sequence determination; we used those sequences to

construct a focal phylogenetic tree of the Cameron Peak

Fire outbreak (Figure 1). In addition, to investigate the

potential for multistate lineage introduction or commu-

nity transmission, we constructed a contextual phylo-

genetic tree by using the 24 whole-genome sequences

of the Cameron Peak Fire specimens and additional

1552 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022

Figure 1. Phylogenetic tree of SARS-CoV-2 consensus whole-genome sequences from 24 of 42 positive specimens from Cameron Peak

reghters available at the Colorado State Public Health Lab with >89% genome coverage. Nodes with at least 95% ultrafast bootstrap

support are labeled. Fireghter crew, sample collection date, and lineage are displayed at the tips. A visualization of the reference genome

is depicted at the top of the phylogeny. Vertical bars shown across each consensus sequence indicate positions of nucleotide changes

relative to the reference genome. High-quality consensus sequences were dened as sequences with >89% genome coverage (10×

sequence coverage depth for Illumina [https://www.illumina.com] and 20× for Oxford Nanopore [https://nanoporetech.com]) and minimum

base quality of 20. Prior to phylogenetic inference, consensus sequences were aligned to the reference genome (Genbank accession no.

NC_045512.2), and insertions were removed so that all sequences were 29,903 nt in length. Phylogenetic inference of the consensus

sequences was performed using IQTree version 2.0.3 (http://www.iqtree.org) with 1,000 ultrafast bootstrap replicates and phylogenetic tree

visualization was performed using the python module ete3 version 3.1.2 (https://pypi.org/project/ete3). Pangolin v.2.4.2

(9) and Nextstrain’s

Nextclade tools (10) were used to assign lineage and clade designations to each assembled genome.

COVID-19 Outbreak among Fireghters, Colorado

whole-genome sequences that were either publicly

available or additionally sequenced at the CDPHE State

Public Health Laboratory (Figure 2; Appendix).

Social Network Analysis

We conducted social network analysis of all

SARS-CoV-2–positive responders by using R Studio

version 1.2.5033 (https://www.rstudio.com) and Ge-

phi Graph Visualization and Manipulation software

version 0.9.2 (https://gephi.org). We applied this

analyis to WGS results to visualize clusters and trans-

mission dynamics among Cameron Peak Fire crews

(11). We assumed epidemiologic links of exposure be-

tween responders belonging to the same crew for net-

work construction. Data showing potential exposure

outside of crew assignments (i.e., socializing with

members of other crews) were not available. This

activity was reviewed by CDC and was conducted

consistent with applicable federal law and CDC poli-

cy (45 C.F.R. part 46, 21 C.F.R. part 56; 42 U.S.C. Sect.

241(d); 5 U.S.C. Sect. 552a; 44 U.S.C. Sect. 3501 et seq).

Results

The outbreak among wildre responders occurred

during August 25, 2020–January 8, 2021. (In Colo-

rado, an outbreak is considered resolved 28 days af-

ter symptom onset of the last case.) A total of 6,123

responders were involved in the response. We iden-

tied 79 cases (78 conrmed and 1 probable); 73 of

these were conrmed to be reghters from 1 of the

63 crews, for an attack rate of 5.8% among 1,260 re-

ghters who were deployed full-time to the incident

(Figure 3). The remainder of responder case-patients

were persons from IMT, equipment operators, and

Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022 1553

Figure 2. Contextual phylogenetic tree and enlarged clades showing genetic relatedness of the Cameron Peak reghter sequences to

sequences of SARS-CoV-2 collected within the United States during September–December 2020. A) Full contextual tree constructed

using 754 contextual sequences subsampled from GISAID (https://www.gisaid.org) plus 24 Cameron Peak reghter consensus

sequences. The phylogeny has been pruned to display 164 contextual sequences and Cameron Peak reghter sequences. Cameron

Peak sequences are highlighted in color according to their lineage assignment. Clades highlighted in gray represent potential community

and interstate transmission events. Cameron Peak sequences assigned to lineage B.1.2 (green) do not cluster together on the contextual

phylogeny to form a monophyletic group, suggesting that they are genetically divergent from one another and likely do not represent a

single transmission event, despite belonging to the same lineage. Mutation dierences among these sequences are shown in detail in

Figure 1. B) Colorado clade 1. Twelve Cameron Peak reghters formed a monophyletic group with sequences from 2 Colorado counties.

C) Colorado clade 2. A single Cameron Peak reghter sequence formed a clade with sequences collected from 3 Colorado counties and

additional sequences collected from outside of Colorado (not labeled). Low support values for this clade may be expected because of

low sequence diversity. D) State 5 clade. The Cameron Peak reghter sequence formed a monophyletic clade with sequences collected

from his or her state of deployment (State 5). E) State 6 clade. The Cameron Peak reghter sequence formed a clade with sequences

collected from his or her state of deployment (state 6) and additional sequences collected from outside of Colorado and not from his or

her state of deployment (not labeled). Low support values for this clade may be caused by low sequence diversity. For panels B–E, all

sequences within a clade are assigned the same lineage. Collection dates are labeled for all tips. Cameron Peak reghter sequences

are highlighted according to their lineage and labeled with crew. Nodes with at least 95% ultrafast bootstrap support values are labeled.

Additional information is available in the Appendix (https://wwwnc.cdc.gov/EID/article/28/8/22-0310-App1.pdf).

SYNOPSIS

paramedics. The 79 case-patients were deployed from

17 states. Of 63 crews, 26 (41.2%) had >1 SARS-CoV-2–

positive responder. Case-patients were primarily

men (83.5%); median age was 39 years (range 20–66

years). Twenty-four (30.4%) case-patients identied

as non-Hispanic, 21 (26.6%) identied as Hispanic or

Latino, and 34 (43.0%) did not disclose ethnicity. Race

was unknown for 34 case-patients (43.0%); 28 (35.4%)

were White, 12 (15.2%) reported other race, 4 (5.1%)

were Black or African American, and 1 (1.3%) was

Native American or other Pacic Islander. A total of

41 (51.9%) case-patients reported symptoms; 4 (5.1%)

reported no symptoms, and symptom information

was unavailable for 34 (43.0%). Thirteen (16.5%) vis-

ited an emergency department, 3 (3.8%) were hospi-

talized, and no deaths were reported.

Among the 79 case-patients, LCDHE completed

interviews with 64 (81.0%). During interviews, these

64 responders identied 273 close contacts who

were contacted by LCDHE and instructed to quar-

antine; however, responders often were unable to

provide specic locations of their camps and were

unable or unwilling to provide names of their close

contacts. Therefore, in addition to routine outbreak

case investigation, LCDHE worked closely with the

IMT’s COVID-19 liaisons for contact tracing. The

COVID-19 liaisons provided documentation of re-

sponders’ crew assignments, which proved to be

a more effective method of contact tracing among

responders than asking case-patients to identify

close contacts during interviews. Because each crew

traveled and camped together, once a case-patient

was identied, their entire crew was considered to

be close contacts and exposed.

Forty (51%) of the 79 SARS-CoV-2–positive

specimens were available for WGS. We obtained

high-quality sequences for 24 specimens, of which

21 were collected during September 1–11, 2020, cap-

turing sequencing data for 87.5% (21/24) of the sam-

ples available from the rst 3 weeks of the outbreak.

In all, we identied 8 lineages (B.1, B.1.2, B.1.240,

B.1.243, B.1.403, B.1.564, B.1.595, and B.1.1.304). Lin-

eages identied near the end of the outbreak (B.1.204,

B.1.243, and B.1.1.304) were not represented in sam-

ples sequenced earlier in the outbreak (B.1., B.1.2,

B.1.403, B.1.564, B.1.595). Two lineages were pres-

ent in >1 crew; for example, lineage B.1.403 was ob-

served in 4 crews and lineage B.1.2 was observed in

3. Three samples were assigned to lineage B.1.2 but

showed divergent nucleotide sequences, suggesting

3 separate introductions of this lineage. In addition,

>1 lineage was identied in 3 crews (Figure 1). For

example, lineages B.1.403 and B.1.2 were both present

in crew B.

We performed contextual phylogenetic analysis

to determine whether interstate or intrastate trans-

mission occurred. We constructed a full contextual

tree by using 717 contextual sequences subsampled

from the GISAID repository (https://www.gisaid.

org), an additional 37 Colorado sequences sequenced

at the CDPHE State Public Health Laboratory, and

the 24 Cameron Peak Fire consensus sequences

1554 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022

Figure 3. Timeline of COVID-19 outbreak among 79 reghters during the Cameron Peak Fire, Colorado, USA, August–December 2020.

COVID-19 Outbreak among Fireghters, Colorado

(Figure 2, panel A). The analysis revealed 4 clades

that provided evidence of possible intrastate and in-

terstate transmission (Figure 2, panels B–E). Twelve

Cameron Peak Fire sequences formed a monophy-

letic clade with sequences collected from 2 Colo-

rado counties with high support values (ultrafast

bootstrap support >95% for nodes; Figure 2, panel

B). Another sequence from a Cameron Peak Fire

responder formed a clade with sequences collected

from 3 Colorado counties and additional sequenc-

es collected from outside of Colorado but with low

support values (ultrafast bootstrap support <95%

for nodes; Figure 2, panel C). In addition, in 2 cas-

es, sequences from 2 different responders formed a

clade with contextual sequences collected from their

state of deployment; 1 clade was supported with

high support values but the other was not (Figure 2,

panels D and E). Although not all clades were sup-

ported with high bootstrap values, low support val-

ues might be expected if sequence diversity is insuf-

cient, which could result from either low diversity

of SARS-CoV-2 circulating in the United States at the

time, or low diversity among samples that were able

to be sequenced and deposited in public reposito-

ries. Short branch lengths as observed on the tree are

indicative of low divergence among sequences (12).

Social network analysis showed the 79 respond-

ers with COVID-19 clustered into 26 crews deploy-

ing from 17 states (Figure 4). Nine crews with re-

sponders from 10 states experienced >3 cases. We

observed multiple lineages within single crews,

suggesting multiple points of introduction, probable

crew intermingling, and possible lapses in preven-

tion measures such as social distancing.

Discussion

The Cameron Peak Fire was the largest recorded wild-

re in Colorado’s history, burning 208,913 acres. A to-

tal of 79 cases of COVID-19 were identied among

Cameron Peak Fire responders deployed from 17

states. Multiple points of SARS-CoV-2 introduction

were likely because of frequent crew turnover as the

wildre grew, as suggested by WGS and social net-

work analysis results.

Balancing management of a large-scale wildre

and control of COVID-19 among responders created

several challenges for disease prevention and mitiga-

tion. Frequent responder turnover because of 2- to

3-week deployments, combined with the length of the

re, resulted in continuous opportunities for intro-

duction of COVID-19 into wildre camps (13). COV-

ID-19 testing was available for incoming responders,

but no testing or quarantine was required upon ar-

rival, and no surveillance testing was required during

the deployment period. In addition, turnover of re-

sponders resulted in several instances in which case-

patients in isolation or contacts in quarantine were

demobilized back to their home states or deployed

to other wildre responses before case investigation

and contact tracing could be completed. In these situ-

ations, CDPHE notied the states to which respond-

ers were demobilized, and LCDHE coordinated with

Cameron Peak IMT to ensure these responders were

immediately notied and given instructions to pro-

ceed home immediately, avoiding contact with others

and stops in indoor public settings during their trav-

el. However, the potential for multistate spread was

a major concern when responders were demobilized

and sent home or to other responses.

Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022 1555

Figure 4. Social network

analysis of Cameron Peak

reghter crews with

COVID-19, Colorado, USA,

August–December 2020. All

responders testing positive

for SARS-CoV-2 (nodes) are

included in this gure to show

contact within crews (edges).

Crews with >3 reghters

positive with SARS-CoV-2

are labeled.

SYNOPSIS

The difculty of screening responders for

COVID-19 symptoms was compounded by challeng-

es differentiating the effects of smoke and high alti-

tude from symptoms of COVID-19. Smoke inhalation

can cause several respiratory symptoms that are simi-

lar to COVID-19, including coughing, shortness of

breath, sore throat, and chest pain (14). Altitude sick-

ness symptoms also overlap with COVID-19 symp-

toms and can include headaches, fatigue, nausea,

and vomiting, as well as, in more severe cases, short-

ness of breath, weakness, and cough (15). Symptoms

of acute and chronic smoke exposure overlap with

and can worsen COVID-19 symptoms, complicating

symptom-based identication of COVID-19 (13,16).

Elevations in the re-affected area ranged from ≈5,200

feet to >10,000 feet, resulting in the potential for alti-

tude sickness for crews, particularly those coming to

Colorado from states at lower elevations.

Often, responders continued to work while they

were symptomatic and infectious and did not report

symptoms until their illness became severe or they

experienced a distinguishing symptom, such as loss

of taste or smell. COVID-19 mitigation was further

challenged by how re camps were set up, poten-

tially increasing exposure opportunities. Crews often

camped together or worked geographically closely

before implementation of mitigation and quarantine

measures, potentially increasing exposure opportuni-

ties. Furthermore, because these camps were often lo-

cated in areas with limited cell service, Wi-Fi hotspots

provided relatively small areas where responders

could access Wi-Fi, creating additional opportuni-

ties for exposure when responders gathered closely

together in areas where Wi-Fi was available (9). Other

barriers to the public health response included some

responders’ distrust of their positive SARS-CoV-2 test

results because of lack of symptoms or overlap with

smoke inhalation symptoms. Further, many respond-

ers were employed as contractors and were not pro-

vided paid sick leave to cover quarantine or isolation.

Fire response coordinators and commanders indicat-

ed that some crew members might have been hesitant

to report symptoms or get tested because of concerns

over having to quarantine or isolate without pay.

Challenges in gathering complete symptom informa-

tion could be caused by responders’ reluctance to be

pulled from their crew, which could further strain

resources during the response. Contact tracing was

challenging early in the investigation because case-

patients were unable to identify their close contacts

or unwilling to provide names of close contacts to

avoid quarantine. Further, responders and response

commanders were resistant to implementing full

quarantines because stafng needs were strained by

the severity of the Cameron Peak Fire and other wild-

res happening concurrently in the region. Critical

infrastructure-modied quarantine and testing-based

strategies were used when full quarantines were not

feasible, including release from quarantine after a

negative RT-PCR result from a specimen collected 7

days after exposure (which was not a recommend-

ed practice under standard quarantine guidance at

that time) or monitoring responders for symptoms

while allowing them to continue working during

quarantine (17).

The results of WGS and social network analysis

suggest multiple SARS-CoV-2 introduction events

throughout the wildre response, as well as spread

both between and within crews. The presence of se-

quences from a single lineage in >1 crew combined

with near-identical nucleotide changes observed

among these sequences suggest intercrew transmis-

sion or transmission between re crews and nearby

communities (Figure 2, panel B). Contextual analy-

sis suggests possible transmission events linked to

Cameron Peak Fire responders from both outside

and within the state of Colorado; in a few instances,

analysis suggested transmission from the state from

which an individual was deployed and in other in-

stances from surrounding counties within the state of

Colorado. One state deployment introduction (state

5) and 1 Colorado county introduction (Colorado

county A) are well supported by bootstrapping, but

in the other 2 instances, support was weak. This result

of low sequence diversity across many states present

in sequences available in public repositories from this

time period.

The rst limitation of our study is that COVID-19

cases were likely underreported because of insufcient

testing and lack of reporting of symptoms by respond-

ers. Surveillance testing was optional and the overlap

between COVID-19 symptoms and symptoms associ-

ated with smoke inhalation and altitude sickness might

have led some persons not to get tested when symptom-

atic. Second, only 51% of outbreak-related specimens

were available for WGS because not all specimens were

sent to the CDPHE laboratory, including those collected

through the local hospital; therefore, results might not

be complete. Finally, social network analysis epidemio-

logic links were assumed for responders on the same

crew but lacked more robust data showing intercrew

mingling during and outside of response activities.

Many lessons were learned in this COVID-19 out-

break during a wildre response. Open communica-

tion between re response agencies and public health

agencies enabled enhanced prevention strategies. Fire

1556 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022

COVID-19 Outbreak among Fireghters, Colorado

response agencies should consider symptom screen-

ing and testing of all arriving responders to limit in-

troduction of SARS-CoV-2 into re camps; educating

responders about potentially overlapping symptoms

of smoke inhalation, COVID-19, and altitude (when

relevant); and improving physical distancing of crews

onsite. Surveillance testing offers the ability to detect

cases early and to prevent transmission before an out-

break occurs (18). Rapid testing options, such as the

use of rapid antigen tests, can provide many benets

in wildre response and other emergency manage-

ment settings, including quick turnaround of results,

which can minimize the need to quarantine critical

responders while awaiting results; encouraging ac-

tion in response to mild symptoms that might other-

wise be dismissed as the result of smoke or altitude,

because it is a quick and easy option to differentiate

symptoms; and ease of implementation in remote

and nonmedical settings, not requiring transport of

persons off-site or coordination with nearby medical

facilities. Response agencies should work with juris-

dictional public health agencies at the beginning of

each response to determine what testing options are

currently available and how best to implement test-

ing of responders. Rapidly identifying cases would

lead to timely case investigations and contact trac-

ing activities that could help mitigate spread of dis-

ease by enabling timely isolation of case-patients and

quarantine of close contacts. Policies to compensate

responders for time spent in isolation or quarantine

could improve compliance with testing and screening

procedures. During the response, re response agen-

cies recommended mask use, especially when other

social distancing measures were difcult to maintain.

Continuing the use of masks in indoor settings or

close interactions with others could be considered in

areas of high transmission even in the absence of local

public health requirements. In current and future re

seasons, we encourage COVID-19 vaccination and

surveillance testing, particularly given the challeng-

es of implementing other mitigation techniques in

resource-constrained re responses. Response agen-

cies should consider collaborating with public health

agencies to ensure that appropriate disease control

measures are put in place when COVID-19 has been

identied among responders, including encouraging

cooperation of persons who are identied as case-

patients or close contacts to prevent the spread of

disease. The lessons learned during this outbreak can

contribute to developing best practices for managing

wildre response and outbreaks of COVID-19 and

other communicable diseases among responders to

large-scale emergency events.

Acknowledgments

We thank the CDPHE Rapid Response Testing Teams

responding to the COVID-19 outbreak at the Cameron

Peak Fire Incident.

About the Author

Ms. Metz works at the Colorado Department of Public

Health and Environment as a COVID-19 Epi Response

Team Unit Manager for metropolitan area counties in

Colorado. Her research interests include infectious disease

epidemiology and outbreak investigations.

References

1. Centers for Disease Control and Prevention. Interim

guidance on developing a COVID-19 case investigation &

contact tracing plan. Appendix A: glossary of key terms.

Close contact [cited 2021 Aug 9]. https://www.cdc.gov/

coronavirus/2019-ncov/php/contact-tracing/contact-

tracing-plan/appendix.html#contact

2. Colorado Department of Public Health and Environment.

Best practices for managing the risks of COVID-19

and wildres. 2020 Aug 24 [cited 2021 Jun 15].

https://covid19.colorado.gov/covid-19-and-wildres

3. Centers for Disease Control and Prevention. FAQs and

communication resources for wildland reghters. 2021

[cited 2021 Jun 15]. https://www.cdc.gov/coronavirus/

2019-ncov/community/wildland-reghters-faq.html

4. United States Department of Agriculture. Wildre smoke

and COVID-19: frequently asked questions [cited 2021 Jun

15]. https://www.nifc.gov/sites/default/les/pio/

documents/Smoke_COVID19_FS_FactSheet.pdf

5. National Wildre Coordinating Group. Fire management

board—COVID-19 information [cited 2021 Jul 30].

https://www.nwcg.gov/partners/fmb/covid-19

6. US Department of Interior Ofce of Wildland Fire. Wildres

and COVID-19 [cited 2021 Jul 30]. https://www.doi.gov/

wildlandre/wildres-covid-19

7. Centers for Disease Control and Prevention. Coronavirus

disease 2019 (COVID-19) 2020 interim case denition,

approved April 5, 2020 [cited 2021 Feb 1].

https://wwwn.cdc.gov/nndss/conditions/coronavirus-

disease-2019-covid-19/case-denition/2020/08/05/

8. Petersen A, Dearing F, Nordgren B. Managing a COVID-19

worst-case scenario: the Cameron Peak Fire story [cited 2021

May 19]. https://experience.arcgis.com/experience/

0d12d48a842745868c1cef3b7b99cd83/page/page_0/

9. Rambaut A, Holmes EC, O’Toole Á, Hill V, McCrone JT,

Ruis C, et al. A dynamic nomenclature proposal for

SARS-CoV-2 lineages to assist genomic epidemiology.

Nat Microbiol. 2020;5:1403–7. https://doi.org/10.1038/

s41564-020-0770-5

10. Hadeld J, Megill C, Bell SM, Huddleston J, Potter B,

Callender C, et al. Nextstrain: real-time tracking of

pathogen evolution. Bioinformatics. 2018;34:4121–3.

https://doi.org/10.1093/bioinformatics/bty407

11. Kırbıyık U, Binder AM, Ghinai I, Zawitz C, Levin R,

Samala U, et al. Network characteristics and visualization of

COVID-19 outbreak in a large detention facility in the United

States—Cook County, Illinois, 2020. MMWR Morb Mortal

Wkly Rep. 2020;69:1625–30. https://doi.org/10.15585/

mmwr.mm6944a3

Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022 1557

SYNOPSIS

12. Guindon S, Dufayard J-F, Lefort V, Anisimova M,

Hordijk W, Gascuel O. New algorithms and methods

to estimate maximum-likelihood phylogenies: assessing

the performance of PhyML 3.0. Syst Biol. 2010;59:307–21.

https://doi.org/10.1093/sysbio/syq010

13. Navarro KM, Clark KA, Hardt DJ, Reid CE, Lahm PW,

Domitrovich JW, et al. Wildland reghter exposure to

smoke and COVID-19: a new risk on the re line. Sci Total

Environ. 2021;760:144296. https://doi.org/10.1016/

j.scitotenv.2020.144296

14. Centers for Disease Control and Prevention. Wildre smoke

[cited 2021 Aug 9]. https://www.cdc.gov/disasters/

wildres/smoke.html

15. Centers for Disease Control and Prevention. Travel to high

altitudes [cited 2021 Aug 9]. https://wwwnc.cdc.gov/

travel/page/travel-to-high-altitudes

16. Henderson SB. The COVID-19 pandemic and wildre

smoke: potentially concomitant disasters. Am J Public

Health. 2020;110:1140–2. https://doi.org/10.2105/

AJPH.2020.305744

17. Centers for Disease Control and Prevention. Testing strategy

for coronavirus (COVID-19) in high-density critical

infrastructure workplaces after a COVID-19 case is

identied [cited 2021 Jun 15]. https://www.cdc.gov/

coronavirus/2019-ncov/community/worker-safety-

support/hd-testing.html

18. Brook CE, Northrup GR, Ehrenberg AJ, Doudna JA,

Boots M; IGI SARS-CoV-2 Testing Consortium. Optimizing

COVID-19 control with asymptomatic surveillance testing

in a university environment. Epidemics. 2021;37:100527.

https://doi.org/10.1016/j.epidem.2021.100527

Address for correspondence: Amanda Metz, Colorado

Department of Public Health and Environment, 4300 Cherry Creek

Dr S, Denver, CO 80246, USA; email: [email protected]

1558 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 8, August 2022

EID

journal

EID

journal

Want to stay updated on the latest news in

Emerging Infectious

Diseases

? Let us connect you to the world of global health.

Discover groundbreaking research studies, pictures, podcasts,

and more by following us on Twitter at @CDC_EIDjournal.

@CDC_EIDjournal@CDC_EIDjournal