Recruitment.

Eligible study participants were current public health practitioners employed by Colorado health departments with direct VBD surveillance responsibilities including collection, management, analysis, or response (e.g., public health leaders, data analysts, epidemiologists, environmental health specialists, public health nurses and administrators). We used a non-probability convenience sampling approach to recruit survey participants and a purposeful sampling strategy [34] to select participants for the semi-structured interviews. Participants were recruited for balanced representation of urban, rural and frontier public health departments [35].

Public health practitioners were recruited in three ways: 1) outreach via e-mail to a Colorado communicable disease network; 2) promotion via monthly call to public health employees; 3) outreach via e-mail by the National Association of City and County Health Officials (NACCHO). Respondents were invited to participate in the electronic survey and upon completion were invited to participate in a 45-minute semi-structured interview. Two follow-up reminder emails were sent to respondents. Every effort was made to schedule interviews within two to three weeks of survey completion.

Exclusion criteria.

We excluded individuals from our survey analysis if they did not provide consent to participate in the survey or if they failed to answer all questions. We excluded participants from participating in the semi-structured interviews if they did not include their name in the survey.

Ethics statement.

Participants were informed of the voluntary nature of this research and provided written consent in the study questionnaire and those invited to be interviewed provided oral consent before beginning the interview which was witnessed by the interviewer and documented via voice recording by the interviewer. This study was approved by the Colorado Multiple Institutional Review Board (COMIRB) (23–1754).

Questionnaire administration.

We developed a 53-question survey adapted from the World Health Organization framework [36]. The survey took 10–20 minutes to complete and included close-ended (e.g., yes/no, multiple choice) and free-response questions to assess public health organizations organizational capacity and resources related to vector-borne surveillance and control activities, and climate risk and vulnerability (S1 Appendix: Survey).

Semi-structured interviews.

An interview guide was developed from the Vanderbilt University Medical Center Community Health Needs Assessment framework [37] and reviewed by infectious disease public health and qualitative method experts. Interview questions were comprised of structured and open-ended questions exploring how participants engaged vector-borne related activities and barriers experienced (S2 Appendix: Interview Guide). Participants were interviewed for approximately 45 minutes by two interviewers. There were no repeat interviews. Insights gained informed subsequent interviews [38]. The interviews were conducted via video conference, dual recorded, and transcribed subsequently using Trint transcription software [39] and edited by the interviewers until they were verbatim. Handwritten field notes were transcribed and included in the thematic analysis. Team-based coding was employed to reach consensus on codes and review emerging themes.

Survey analysis.

We evaluated responses to survey questions about public health organization surveillance and response capacity to vector-borne disease threats. In cases where multiple individuals from the same health department responded to the survey (n = 3), an individual was selected at random so that each health department was represented an equal number of times in the survey data for analysis. We excluded from the analysis: responses to 16 questions due to low response counts and questions with less than 5 responses, which primarily occurred due to branching logic of the survey.

Counts (n) and percentages (%) were computed for all multiple-choice questions related to vector-borne disease surveillance and control capacity within public health organizations. Responses related to climate risk and vulnerability are reported elsewhere. Responses to open-ended questions were reviewed and manually assigned to corresponding levels. Survey responses were stratified by populations served: < 10,000, 10,000–50,000; 51,000–100,000; > 100,000 to assess differences across public health organizations that service populations reflective of frontier (population density of six or fewer persons per square mile), rural (non-metropolitan counties without cities of 50,000 or more residents) and urban (population of 50,000 or more, including large towns [51–100K] and cities [100K+]) areas [35]. We also evaluated responses from participants with missing name information to assess if those respondents were different from other respondents.

Supplemental analyses included multiple component analyses (MCA) to evaluate relationships among survey responses and determine if differences of survey responses by population size were present; and display 2023 rates of WNV among public health organization participants (S1 Text). Survey data were analyzed using R (version 4.1.2) [40].

Thematic analysis from interviews.

Thematic analysis was performed by two study team members (JB and JC) in an iterative manner to conceptualize the data, group concepts into patterns and relationships, and analyze across cases for similarities and differences. Results are based on case experiences and feedback, and were identified by comparing the case to negative-case sites. Data were analyzed using both inductive and deductive coding. The study team members read through the interview records to become familiar with their content before coding. A deductive codebook was developed based on the interview guide. Inductive codes were added to the codebook as identified during coding. Twenty percent of the interviews were dual coded, and the coding team worked to find consensus on codes and code definitions to establish coding consistency. Team meetings were held where codes were compared and discrepancies addressed and reconciled, and additional study team members (JGB and TMQ) provided content and methodological input. Memos were created to capture preliminary ideas about potential themes and describe illustrative cases. Themes were finalized through a process of running queries of the data, and comparing and reconciling emerging ideas into preliminary themes until a point of saturation was reached. Documents were read, coded and linked to the interview data to triangulate information from multiple sources, participants, and points in time. Atlas.ti (version 24.1.1) software was used for all thematic coding and analysis [41].

Reported VBDs and perceptions of VBD burden on priority setting.

The most common VBD reported in the past 12 months by survey was West Nile Virus (82%) followed by plague (32%), spotted fever group rickettsiae (SFGR) (28.6%) and tularemia (25.0%) (Fig 3B). Lyme disease (32%) and dengue virus (DENV) (29%) were also reported as travel acquired diseases (Fig 3B). The higher annual incidence rates of WNV observed across many counties was also highlighted as a concern by interviewees underscoring the importance of prioritizing VBDs. As one respondent told us “… Colorado has typically and historically had pretty high cases of human West Nile virus. We just had a close to a record-breaking year the summer of 2023. We had over 600 human cases. And that’s a disease of, you know, not only that can cause death… it requires a lot of treatment, hospitalization, sometimes followed by extensive physical therapy afterwards.” (Veterinary Epidemiologist, 100K+) The predominance of WNV in Colorado is also supported by other documents. For example, in 2023, Colorado experienced the worst WNV outbreak in the U.S. and one of the deadliest years for WNV since its arrival in the U.S. in 1999 [42] (Table 2). A health advisory on July 6, 2023 also noted WNV had been detected during routine mosquito surveillance in Boulder, Delta, Larimer and Weld counties (Table 2) [42]. In a press release disseminated in August of 2023, the state epidemiologist noted “the trends we are seeing in our West Nile virus tracking data are unprecedented” (Table 2) [43].

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Table 2. Additional Data Sources for Contextualizing Cases.

https://doi.org/10.1371/journal.pone.0347142.t002

In areas where VBD burden is consistently low, interviewees described uncertainty in whether there is justification for prioritizing resources devoted to VBDs, “… you see programs like in Larimer County where they’re doing more surveillance. And we are, you know, lacking that. So do we have a problem? Don’t know, because we’re not looking for anything.” (Administrator, 10-50K) The perceived burden of disease was a key factor in determining whether public health organizations prioritize VBD activities.

Vector surveillance and control organizational capacity and training needs.

Limited vector surveillance activities were reported in both surveys and interviews. Only nine public health organizations (38%) reported routine vector surveillance (defined as vector collection and/or vector pathogen testing) (Table 3). For the public health organizations conducting vector surveillance, 89% conducted vector collections, but only 11% engaged in pathogen testing, and half (56%) conducted activities during the summer. Survey responses showed that capacity for vector surveillance activities differed by population size (Table 3). Those conducting their own vector surveillance were often (63%) from larger populations (i.e., 100,000 residents or more).

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Table 3. Vector Surveillance, Control and Resource Activities of 24 Colorado Public Health Organization Respondents Surveyed from January to May 2024.

https://doi.org/10.1371/journal.pone.0347142.t003

Interviewees highlighted the disparity in mosquito surveillance across Colorado, particularly underscoring the need for programs in rural and frontier counties, “...I think the increased capacity for mosquito surveillance [is needed] for all parts of the county and not just, you know, the suburban ones, because I feel like that’s where a lot of, you know, effort is spent in the more populated areas. But that doesn’t mean that people aren’t living in the rural or frontier parts [of the] county that also need this sort of information or tools.” (Infectious Disease Epidemiologist, 100K+)

Reported vector control capacity (defined as vector spraying or other vector population reduction activities, and insecticide resistance monitoring) was sparse across the public health organizations. While 46% of 24 public health organizations reported conducting vector control activities for mosquitoes (defined as chemical, biological, source reduction, or environmental management), only 17% of public health organizations performed insecticide spraying for any vector (Table 3). Of those who applied insecticides, 75% reported doing so weekly during the summer months and also were more likely to report conducting vector surveillance activities (50%). However, most respondents (88%) reported they did not conduct insecticide resistance testing, and 12% responded they do not know or were unsure.

Vector pathogen testing equipment and insecticide application resources were largely unavailable to public health organizations. Only 13% of respondents reported having reliable in-house testing equipment and 17% reported having up-to-date insecticide application equipment (Table 3). Most respondents (83%) also reported using outside laboratories for testing. When asked what additional testing methods practitioners would like to use in their organization, but do not currently have the resources for, 33% reported insecticide resistance testing, 17% pathogen testing, and 50% were unsure. Vector surveillance (42%) and vector control trainings (21%) were reported as the most important type of training needed in their organizations. In person, onsite trainings was the modality preferred by 46% of respondents.

Challenges to VBD mitigation efforts.

Resources (e.g., programmatic funding, technological tools, and trainings) were the most important barrier to VBD prevention and control reported by public health organizations (46%), followed by personnel funds (33%) and other (21%) (Fig 3C). The “other” category reflects community buy in, political will, prioritization. Interviews highlighted limits on public health organization capacity, specifically, noting no ability to carry out active mosquito surveillance or control activities within their public health organizations. “Most jurisdictions in Colorado don’t have the capabilities to do any mosquito control, and they are relying solely on their residents protecting themselves.” (Program Manager, 100K+)

The overwhelming majority of interviewees reported that mosquito control activities are contracted out to external organizations, which is consistent with only 46% of public health organizations who reported conducting control activities for mosquitoes in the survey. “I think here [mosquito surveillance] it’s contracted out. I’m actually not certain exactly what we do. But I know that, like, nobody on our team is...going collecting mosquitoes or anything like that.” (Senior Epidemiologist, 100K+) In the smallest (<10K) communities’ resources were of most concern (67%), while personnel funds and other barriers were more commonly reported among respondents from public health organizations serving communities with 10-100k residents (Fig 3C). Training as a barrier was only reported for population size 10-50k. Interviewees cited similar challenges, such as the time intensive nature of finding skilled public health practitioners and the extensive training required for the position. “…I think our capacity is-- just our sometimes our lack of humans or lack of staff. If things get out of hand, we do jump in, you know?... but then you’re looking at just-in-time training.” (Disease Control Specialist, 51-100K)

Lack of standardization and integration of vector-borne disease data.

Respondents reported data modernization, standardization and integration challenges with vector-borne disease data. They reported difficulty in managing surveillance systems, accessing historical case data and linking related vector data across different platforms, as described by this participant, “So that’s one thing that we’ve been lacking. We’ve been housing our vector-borne data in a very outdated, really not very functional database.” (Program Manager, 100K+)

Many respondents mentioned the upcoming transition to the EpiTrax system [a new core disease surveillance system that will consolidate the functions of 10 + existing State surveillance systems and modernize Colorado’s disease control infrastructure] may alleviate some of these concerns by allowing for visualizing disease trends and understanding real-time disease incidence. As one interviewee noted, “...I think this is hopefully in the plans with the EpiTrax rollout…we have a separate like, the animal stuff lives in a separate database. So. It’s tricky to manage multiple surveillance systems. So, integrating all of those would be amazing.” (Epidemiologist, 10-50K)

A Colorado Department of Public Health & Environment FY 2023–2024 Funding Request for the EpiTrax Disease Surveillance Platform [47] supported these sentiments noting, “the State’s systems are outdated, unreliable, and poorly supported” and “modernization of disease reporting infrastructure will prepare the Department for future pandemics and outbreaks as well as daily disease control and prevention efforts.” Improvements in surveillance systems can provide the data needed for geographic information system (GIS) analyses. 67% of public health organizations report having staff who perform GIS (Table 3), enabling more precise mapping of vector populations, identification of historical trends, and detection of high-risk areas.

Reactionary response to vector-borne outbreaks.

Interviews revealed many public health organizations have operated “more reactionary” in response to current and ongoing public health threats with less focus on prevention measures. As noted by one interviewee, “...right now we’re not really all that active. We’re really reactive… it would probably be more useful if we were looking--like regularly looking--in areas that are likely places that those ticks might settle in Colorado, and we just don’t have the resources to do that.” (Program Manager, 100K+)

Many respondents highlighted the need for more “proactive [surveillance] efforts” and underscored that their day-to-day activities involve mostly response efforts with little bandwidth for additional planning and preparation for future outbreaks, as described by one interviewee, “…when I think of, our vector disease, we’;re able to do the day-to-day response, investigate the disease issues that come up. Outside of that, we’re not doing a ton of other sort of proactive planning efforts...” (Program Coordinator, 100K+) Rather than engaging in prevention techniques consistently to proactively approach VBDs in their communities they often only increase efforts when an outbreak occurs.

Perceived lack of support and threats to sustainable funding.

Interviewees reported struggling to maintain sustainable funding for VBD programs that enhance prevention efforts and highlighted how difficult it is to convey disease mitigation successes. As noted by one interviewee, “I think for, for most folks, just really trying to secure sustainable funding, for what we’re trying to do now, let alone being able to expand in the future and not have it just be reactionary. That is, unfortunately though the, the recipe I’ve seen throughout my career is we have to wait for things to get to a pretty catastrophic level before we start allocating funds for it. We don’t stay in the proactive prevention stage, but nobody can see those results. You don’t see all the things [local public health agencies] didn’t allow to happen. So that’s the challenge.” (Program Coordinator, 100K+)

Interviewees reported difficulty ascertaining additional funds to support lasting VBD surveillance and control activities when disease priorities shifted in the community. National and state funding for VBDs did not meet the reported needs for maintaining a robust VBD program. As reported by a participant, “…There aren’t good funding sources for vector programs. If the county isn’t allocating money, there isn’t state and federal dollars trickling into the local health departments to run these programs.” (Program Coordinator, 100K+) In 2023, 2.3% of the FY 2022–2023 state operating budget was allocated to Public Health and Environment (i.e., $913.5 million dollars) [48]. The Centers for Disease Control and Prevention (CDC) fiscal year (FY) 2023 Grants Summary Profile Report for Colorado describes selected CDC grants and cooperative agreements provided to health departments, universities, and other public and private agencies in Colorado. In 2023, a budget of $7.6 million dollars was allocated to Colorado for Emerging and Zoonotic Infectious Diseases, with VBDs receiving only $1.8 million (24%) of those funds [46]. CDC Public Health Emergency Preparedness reports show funding for fiscal years (FY) 2021–2023 for Colorado remained consistently in the range of $10.2-$10.8 million dollars [45] to support frequent public health emergencies including infectious disease outbreaks. Outside of emergency scenarios, consistent long-term funding was largely reported as being inaccessible and sporadic for VBD programs. Furthermore, interviewees reported that after an emergency concludes federal funding “goes away” and the “infrastructure [is] dissolved because it’s not sustainable.” (Program Manager, 100K+)

Importance of engaging in community education and building buy-in.

The importance of building stronger partnerships with health care providers, increasing community engagement, and enhancing public understanding of vector diseases was also highlighted by interviewees. “… I really, really think a lot of it is that not everyone is aware that [VBD] is a danger... [there is a] lack of providers who are literate, especially having tick borne illnesses [in Colorado].” (Epidemiologist, 100K+)

Respondents expressed concern with the lack of public knowledge of VBDs and the dangers surrounding human interaction with wildlife and the potential for increased disease transmission. “...But I think the community as [a] whole doesn’t understand public health, vector being just one of the many programs dealing with diseases they don’t understand.” One interviewee mentioned their VBD program had “no active engagement of the community for them to fully understand some of the [vector-borne] disease and risks.” (Program Coordinator, 100K+) Survey findings support these assertions with 42% of public health organizations reporting that they do not conduct any community outreach activities.

Respondents also underscored the critical role the community plays in supporting VBD programs and initiatives. “I think the community is a critical stakeholder and they’re the ones who are trying to act. So again, I would say that the information exchange [from the public health organization] with the community is probably the weakest link... I don’t think people always consider the community as a critical stakeholder.” (Program Coordinator, 100K+) Further, respondents expressed concerns about the community as a potential barrier to funding sources if the public were to withdraw support for VBD containment and mitigation strategies. “…convincing people that vector-borne illnesses are a priority, especially if they’re worried about other things like economic downturn or childcare. Like, it’s pretty low on most people’s priorities.” (Infectious Disease Epidemiologist, 100K+)

This was underscored by respondents reporting concern for pesticide use as one main challenge that could lead to the abolishment of VBD surveillance and control programs if discontentment is strong enough. “So getting one of the biggest, biggest problems that we’re facing now with West Nile is the lack of resources at the local level to conduct evidence-based mosquito control and mosquito surveillance specifically for West Nile vectors. As well as some pushback from communities about using pesticides to spray.” (Program Manager, 100K+)

Cases and negative cases across population sizes.

When comparing cases and negative cases, cases reported a heightened sense of urgency and both internal (e.g., leadership expectations) and external pressure (e.g., community concerns) to address VBDs, whereas negative cases did not report similar drivers to prioritize VBDs. Public health organization cases were mostly from large populations of 100K+ (n = 10; 67%) and expressed concerns about the recent increase in VBDs. The three negative cases represented public health organizations from populations < 100K (<10K, 10-50K, 51-100K). The burden of human cases of VBD in negative case public health organizations were reported in interviews to be low to nonexistent, instead prioritizing surveillance and control activities for foodborne and respiratory illnesses.

Many case interviewees mentioned investigating human cases of reported VBDs with no active vector species surveillance efforts to guide control measures. Cases also mentioned that their communities’ echoed concerns of VBD prioritization especially when observing dead animals in wild (birds) that may carry vector-borne related disease. Negative public health organization cases rarely had reports of human VBD cases in their communities; however, interviewees mentioned they occasionally got reports of human exposure to dead animals, mainly bats, and described an increased incidence of equine WNV in neighboring counties. This did not bring external pressure or concern from their communities for VBDs. Negative case interviewees also highlighted that because they do not perform surveillance of these vectors, they cannot be confident as to whether or not vector species of concern exist in their area.

While both case and negative case interviewees mentioned sending vector species samples to outside testing laboratories, cases mentioned being able to do so with greater support through internal funding and capacity structures. Negative cases reported having limited resources to test samples of animals and vectors for pathogens at an outside laboratory. One negative case interviewee mentioned that their community is in a remote, rural area with geographical barriers to mailing specimens, especially during winter months when snowy conditions can make transportation more difficult. Interviewees from negative case public health organizations mentioned community partners (i.e., veterinarians, the public) may bring in samples for pathogen testing but underscored that the sender is often responsible for the associated cost. To circumvent this, these community public health organizations described applying to grants that will support sample testing kits and fees.

Cases were more likely to report being located in urban settings at lower elevations where humans, infected wildlife, and vectors have the potential to be in close contact. Case interviewees reported human cases of VBDs mostly originating from within their county, with travel acquired cases occurring secondarily. This differs from negative case public health organizations where interviewees reported working in areas with high elevation levels that aren’t currently ecologically suitable for vector species. When human cases were reported within these negative case counties, interviewees noted that they were almost always travel related cases acquired from a different state within the US or from travel outside of the US.

Community education was described as an important measure by both negative case and case interviewees. Negative case interviewees were concerned that strain from the COVID-19 pandemic impacted established relationships with the general public and community institutions (schools, hospitals, nursing homes, jails). They mentioned that the general public may not be aware of the public health organization disease reporting phone lines or that individuals should call in if they have a vector-borne disease exposure. Similarly, cases stressed the importance of educating the public on how to keep themselves and their environment safe from vector-borne diseases and why it is important to be aware of these vectors ability to transmit disease especially during the summer months.

Negative cases mentioned they’ve had “tremendous turnover” of staff in recent years since the COVID-19 pandemic and have found it difficult to attract skilled public health practitioners to their more remote areas. Moreover, multiple negative case interviewees mentioned that they are solely responsible for their infectious disease case investigation and response without “backups” for their roles in either function or disease knowledge. They noted that being the only staff member responsible for these tasks can create a delay in response to investigation if they are out of the office and expressed concern that their public health organizations would lack the capacity to address a future disease outbreak. Case public health organization interviewees reported having a collaborative internal structure that promotes working with other epidemiologists and environmental health specialists to conduct surveillance and control activities.