Threats to public health workers.

Media reports and data from public health professional membership organizations have demonstrated high levels of harassment experienced by public health workers throughout the COVID-19 response. We documented personal and political threats to public health workers across the first 12 months of pandemic response through a longitudinal survey completed in Fall 2020 and Summer 2021. The web-based survey was distributed to respondents using the Qualtrics survey platform. Survey items measured domains including demographic information, public health roles and training, mental and physical health, and work-life balance. Respondents were also asked if they had received any personal or political threats, from whom these threats were received, and completed an open-ended question describing the nature of the threats. Among the 85 public health workers completing both surveys, threats from members of the public and from elected and appointed leaders were most prevalent at both timepoints; however, as the pandemic response progressed, the nature of threats to public health workers changed. While those remaining in the public health workforce may be more resilient to these threats, increased prevalence of personal and political threats has the potential to deter new graduates from entering the field, impacting the public health system's future response capacity.

Changes in anxiety and depression among public health workers during the COVID-19 pandemic response.

OBJECTIVES: The COVID-19 pandemic has negatively impacted mental health indicators, leading to an increase in symptoms of anxiety and depression in both the general population of adults and children and many occupational groups. This study aims to examine changes in anxiety and depression among a cohort of public health workers in the U.S. during the first year of the COVID-19 pandemic and identify potential risk factors. METHODS: Longitudinal data were collected from a sub-sample (N = 85) of public health workers in 23 U.S. states who completed two surveys in 2020 and 2021. Information on background characteristics, personal well-being, and work environment as well as validated scales to assess generalized anxiety disorder (GAD), depressive disorder, and burnout was collected. Data were analyzed using Stata Version 17, and significant differences were determined using Pearson's Chi2 and Fisher's Exact tests. RESULTS: The proportion of those reporting GAD (46.3% to 23.2%) or depression (37.8% to 26.8%) improved from Survey 1 to Survey 2 overall; symptoms of anxiety saw the largest improvement. Persistent depression was associated with sustained burnout, changes in social support, and days worked per week. CONCLUSION: Public health workers experienced elevated levels of anxiety and depression during the initial pandemic response, but a reduction in these symptoms was observed in the subsequent year after vaccines had become widely available. However, unmet needs remain for ongoing workplace mental health supports to address burnout, as well as for additional emotional supports outside of work for public health professionals.

Social Media Usage as a Form of Breastfeeding Support Among Black Mothers: A Scoping Review of the Literature.

INTRODUCTION: Social support has been identified in the literature as a key facilitator of breastfeeding success among Black mothers. Over the past decade, there has been a surge of social media groups that can now be used as a means of support for various health and social issues. Social media breastfeeding groups have been used as sources of additional support. A scoping review of the literature was conducted to explore social media usage as a form of social support among Black women in the postpartum period and how it may affect breastfeeding behaviors. METHODS: Using the 5-stage scoping review methodology, scholarly databases were searched for relevant articles. English-language articles on studies conducted both in and outside of the United States were included. Original studies that focused on social media as a form of breastfeeding support and included Black mothers as part of the study population were included. RESULTS: After screening 551 articles, 6 studies fulfilled the study criteria. Participants reported being provided with various forms of social support through social media within the included articles. Primary themes included (1) a sense of community and (2) self-efficacy and empowerment. Breastfeeding support through social media appears to positively influence breastfeeding intention and duration rates among Black mothers. DISCUSSION: Social media is an accessible avenue for breastfeeding information and support. Moreover, it provides a safe space for Black women to interact with others of shared cultural experiences. Therefore, incorporating social media into breastfeeding interventions can positively affect breastfeeding rates among Black women. More research is needed to assess the direct effect of social media breastfeeding support groups on the breastfeeding behaviors and experiences of Black women.

Determinants of Under-Five Mortality in an Armed Conflict Setting: Empirical Findings from the Demographic and Health Surveys.

Insurgencies like Boko Haram may impact the physical health and well-being of adults and children living in geographic areas under their political control. However, it is difficult to obtain reliable health data in conflict-affected areas. This study explored the potential to use data from the Demographic and Health Surveys (DHS) to examine the determinants of under-five mortality in Northern Nigeria. Data were derived from DHS conducted before and after the start of the Boko Haram insurgency in 2009. A multi-level mixed effects logistic regression model was used to identify predictors of under-five mortality in an armed conflict setting. Results were reported as adjusted odds ratios (aOR) and 95% confidence intervals (CI). Residence in an armed conflict setting was not significantly associated with under-five mortality (aOR = 1.06; 95% CI: 1.00, 1.10). However, twin gestation (aOR = 3.18; 95% CI:2.96, 3.42), wealth index of family (richest versus poorest: aOR = 0.42; 95% CI: 0.37, 0.47), religion of mother (Islam versus Christianity: aOR = 1.50; 95% CI: 1.43, 1.57); highest educational level of mother (higher versus none: aOR = 0.33; 95% CI: 0.29, 0.37), and parity of mother, significantly predicted death before the fifth birthday. Repeated studies are needed to assess the impact of Boko Haram insurgency on physical health outcomes, particularly in areas where primary data collection is difficult or impossible.

Lessons Learned From the Public Health Workforce's Experiences With the COVID-19 Response.

Limited research is available on the COVID-19 response experiences of local, state, and federal public health workers in the United States. Although the response to COVID-19 is still presenting challenges to the public health workforce, public health systems must also begin to consider lessons learned that can be applied to future disasters. During July and August 2021, a random sample of participants from a cross-sectional study of the public health workforce was invited to participate in interviews to obtain information on the current state of public health operations, the ongoing response to the COVID-19 crisis, and takeaways for improving future preparedness and response planning. Interviews were transcribed and inductively coded to identify themes. Twenty-four initial interview invitations were sent, and random substitutions were made until thematic saturation was reached when 17 interviews were completed. Four thematic categories were identified, including challenges related to (1) ongoing lack of political support or policy guidance; (2) fluctuations in, and uncertainty about, future funding and associated requirements; (3) job expectations, including remote work and data-sharing capabilities; and (4) the mental health toll of sustained response and related burnout. As the public health response to the COVID-19 pandemic continues in its third year, it is crucial to identify lessons learned that can inform future investment in order to sustain a public health workforce and a public health preparedness and response system that is resilient to future disasters.

Epidemiology Surveillance and Capacity Improvement: A Characterization of Texas, 2017.

OBJECTIVES: In response to increasing caseloads of foodborne illnesses and high consequence infectious disease investigations, the Texas Department of State Health Services (DSHS) requested funding from the Texas Legislature in 2013 and 2015 for a new state-funded epidemiologist (SFE) program. METHODS: Primary cross-sectional survey data were collected from 32 of 40 local health departments (LHDs) via an online instrument and analyzed to quantify roles, responsibilities, and training of epidemiologists in Texas in 2017 and compared to similar state health department assessments. RESULTS: Sixty-six percent of SFEs had epidemiology-specific training (eg, master's in public health) compared to 45% in state health department estimates. For LHDs included in this study, the mean number of epidemiologists per 100 000 was 0.73 in medium LHDs and 0.46 in large LHDs. SFE positions make up approximately 40% of the LHD epidemiology workforce of all sizes and 56% of medium-sized LHD epidemiology staff in Texas specifically. CONCLUSIONS: Through this program, DSHS increased epidemiology capacity almost twofold from 0.28 to 0.47 epidemiologists per 100 000 people. These findings suggest that capacity funding programs like this improve epidemiology capacity in local jurisdictions and should be considered in other regions to improve general public health preparedness and epidemiology capacity.

Changes to Timeliness and Completeness of Infectious Disease Reporting in Texas After Implementation of an Epidemiologic Capacity Program.

OBJECTIVES: The objective of this study was to characterize the changes in timeliness and completeness of disease case reporting in Texas in response to an increasing number of foodborne illnesses and high-consequence infectious disease investigations and the Texas Department of State Health Services' new state-funded epidemiologist (SFE) program. METHODS: We extracted electronic disease case reporting data on 42 conditions from 2012 through 2016 in all local health department (LHD) jurisdictions. We analyzed data on median time for processing reports and percentage of complete reports across time and between SFE and non-SFE jurisdictions using Mann-Whitney t tests and z scores. RESULTS: The median time of processing improved from 13 days to 10 days from 2012 to 2016, and the percentage of disease case reports that were complete improved from 19.6% to 27.7%. Most reports were for foodborne illnesses; both timeliness (11 to 7 days) and completeness (20.9% to 23.5%) improved for these reports. CONCLUSIONS: Disease reporting improvements in timeliness and completeness were associated with the SFE program and its enhancement of epidemiologic capacity. SFEs were shown to improve surveillance metrics in LHDs, even in jurisdictions with a high volume of case reports. Adding epidemiologist positions in LHDs produces a tangible outcome of improved disease surveillance.

Quantifying Disaster Impacts on Local Public Health Agency's Leadership, Staffing, and Provision of Essential Public Health Services.

OBJECTIVE: The objective of this study is to assess the impact that natural disaster response has on local health departments' (LHD) ability to continue to provide essential public health services. METHODS: A web-based survey was sent to all North Carolina Local Health Directors. The survey asked respondents to report on LHD functioning following Hurricanes Florence (2018) and Dorian (2019). RESULTS: After Hurricane Florence, the positions who most frequently had regular duties postponed or interrupted were leadership (15 of 48; 31.3%), and professional staff (e.g., nursing and epidemiology: 11 of 48; 22.9%). Staffing shelters for all phases - from disaster response through long-term recovery - was identified as a burden by LHDs, particularly for nursing staff. Approximately 66.6% of LHD jurisdictions opened an Emergency Operations Center (EOC) or activated Incident Command System in response to both hurricanes. If an EOC was activated, the LHD was statistically, significantly more likely to report that normal duties had been interrupted across every domain assessed. CONCLUSIONS: The ability of LHDs to perform regular activities and provide essential public health services is impacted by their obligations to support disaster response. Better metrics are needed to measure the impacts to estimate indirect public health impacts of disasters.

A Qualitative Study of the COVID-19 Response Experiences of Public Health Workers in the United States.

The mental health impacts of the COVID-19 pandemic on frontline, patient-facing healthcare staff have been described in several studies, but the effects of the COVID-19 response on the US public health workforce have not been well characterized. In early 2021, we conducted interviews with a subset of public health practitioners in the United States who participated in a cross-sectional survey and indicated their willingness to participate in a follow-up interview. An interview guide was developed to collect information about professional roles since the start of the pandemic, aspects of the individual COVID-19 response that impacted mental health, and aspects of the organizational/institutional COVID-19 response that impacted mental health, as well as the strengths and weaknesses of, opportunities for, and threats to public health professionals and organizations going forward. Interviews were transcribed and inductively coded to identify themes. Of the 48 people invited to participate, 24 completed an interview between January 28 and February 23, 2021. Five key themes were identified through inductive coding of interview transcripts: (1) teamwork and workplace camaraderie, (2) potential for growth in the field of public health, (3) considerations for adaptive work environments (eg, remote work, work out of jurisdiction, transition to telework), (4) politicization of response, and (5) constrained hiring capacity and burnout. After more than a year of public health emergency response to the COVID-19 pandemic, it is critically important to understand the detrimental and supportive factors of good mental health among the public health workforce.

The impact of the COVID-19 response on the provision of other public health services in the U.S.: A cross sectional study.

INTRODUCTION: Funding and staff formerly dedicated to routine public health tasks (e.g., responding to communicable and non-communicable diseases, investigating foodborne outbreaks, conducting routine surveillance) and services (e.g., environmental health, substance abuse, maternal-child health) may no longer be available in many public health departments due to the COVID-19 response. The objective of this study was to assess the extent to which staffing for essential public health services has been redirected to the COVID-19 response. MATERIALS AND METHODS: This is a cross-sectional study using a survey distributed through the Qualtrics platform. Individuals (N = 298) working in public health across governmental and academic public health departments in the U.S. during the ongoing COVID-19 pandemic response were surveyed. Survey items measured multiple domains including professional experience (i.e., training, years of experience, content expertise, job functions, hours worked), mental and physical health status (i.e., generalized anxiety, depression, burnout), and career plans (i.e., pre-pandemic vs. current career plans). RESULTS: The total number of content expertise areas and programmatic functions covered by individual public health workers increased between January and September of 2020, with 26% (73 of 282) of respondents reporting an increase in both. The total number of respondents working in infectious disease and preparedness remained constant, while declines were reported in program evaluation (-36%) and health education (-27%) and increases were reported in disease investigation (+35%). CONCLUSIONS: The provision of many essential public health functions and tasks have been limited or eliminated while the U.S. public health workforce responds to the COVID-19 pandemic. These findings highlight opportunities for funding and professional development of public health systems, both during and after the COVID-19 response, to help ensure the continuity of essential public health services, staffing sustainability, and preparedness for future public health emergencies in the U.S.

Public Health Workforce Burnout in the COVID-19 Response in the U.S.

While the health impacts of the COVID-19 pandemic on frontline health care workers have been well described, the effects of the COVID-19 response on the U.S. public health workforce, which has been impacted by the prolonged public health response to the pandemic, has not been adequately characterized. A cross-sectional survey of public health professionals was conducted to assess mental and physical health, risk and protective factors for burnout, and short- and long-term career decisions during the pandemic response. The survey was completed online using the Qualtrics survey platform. Descriptive statistics and prevalence ratios (95% confidence intervals) were calculated. Among responses received from 23 August and 11 September 2020, 66.2% of public health workers reported burnout. Those with more work experience (1-4 vs. <1 years: prevalence ratio (PR) = 1.90, 95% confidence interval (CI) = 1.08-3.36; 5-9 vs. <1 years: PR = 1.89, CI = 1.07-3.34) or working in academic settings (vs. practice: PR = 1.31, CI = 1.08-1.58) were most likely to report burnout. As of September 2020, 23.6% fewer respondents planned to remain in the U.S. public health workforce for three or more years compared to their retrospectively reported January 2020 plans. A large-scale public health emergency response places unsustainable burdens on an already underfunded and understaffed public health workforce. Pandemic-related burnout threatens the U.S. public health workforce's future when many challenges related to the ongoing COVID-19 response remain unaddressed.

Leveraging Household Structure for Increasing Adult Physical Activity in a Low-Income, African American Community.

Health behavior changes often require focusing on factors beyond the individual, particularly in low-income and underresourced areas. The purpose of this article was to assess associations between household structure and adult physical activity levels. Data were collected using Community Assessment for Public Health Emergency Response methodology to administer a household survey (n = 100). Household structure was calculated from summing the number of adults (⩾18 years) and children (<18 years) reported living in the house. Physical activity was measured using the International Physical Activity Questionnaire-Short Form. Adults living in households with two or more adults reported more MET (metabolic equivalent of task) minutes of physical activity per week than adults from households with only one adult. Adults living in households with two or more adults were twice as likely to meet aerobic guidelines for physical activity compared to adults living in households with only adult. Findings suggest the need for developing ecologic approaches in low-income communities to increase social support for physical activity in adults.

How Do Infectious Disease Epidemiologist Positions Increase Public Health Capacity? Results from a Qualitative Study of Local Health Departments.

The purpose of this study was to characterize changes in and impacts on epidemiologic capacity in local health departments after the implementation of a state-funded epidemiologist program using qualitative data. The study used key informant interviews in Texas health departments, which were conducted and inductively analyzed to identify themes. Five predominant themes emerged from interviews on the impact of state-funded epidemiologists on the epidemiology capacity of local health departments. State-funded epidemiologists were seen as increasing overall epidemiology capacity in local health departments. Specifically, they improved timeliness of infectious disease reporting and quality and thoroughness of disease investigations. They also improved community stakeholder relationships with local health departments and communications across local, regional, and state public health agencies. Key informants at all levels described positive effects of the state-funded epidemiologists on disease surveillance. Local epidemiology capacity has increased, and, in turn, Texas public health surveillance capacity has improved at the local, regional, and state levels. Funding programs like this should be considered when public health capacity is low and in need of an increase.

A Spatial Analysis of Possible Environmental Exposures in Recreational Areas Impacted by Hurricane Harvey Flooding, Harris County, Texas.

Hurricane Harvey made landfall on the Texas Gulf Coast in August 2017 causing catastrophic flooding. Harris County is highly vulnerable to flooding, which is controlled in part by a system of bayous that include parks and trails. The petrochemical industry, as well as thousands of documented sources of environmental pollution make recreational areas susceptible to environmental contamination during flood events. Recreational areas and toxic exposure sources were geocoded by subwatershed boundaries and overlaid with the area of Hurricane Harvey inundation. A total of 121 of 349 (36.78%) parks were flooded; 102 of 121 (84.30%) were located in subwatersheds with at least one exposure source. A total of 337 exposure sources (6 Superfund, 32 municipal solid waste, and 299 petroleum storage tanks) in 30 subwatersheds were flooded. Though parks provide flood mitigation and other postdisaster benefits, their susceptibility to environmental contamination should be considered, especially in areas with a large number of toxic exposure sources.

Using Spatial Analysis to Examine Potential Sources of Polycyclic Aromatic Hydrocarbons in an Environmental Justice Community After Hurricane Harvey.

Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants associated with adverse human health outcomes. Environmental justice neighborhoods experience disproportionate environmental health risks. Hurricane Harvey made landfall on August 25, 2017, bringing record rainfall and catastrophic flooding to Houston, Texas, redistributing PAHs in residential soil. We aimed to describe PAH distributions in soil in the Manchester neighborhood of Houston, TX, and identify their potential sources. Soil samples were collected from 24 residential addresses and analyzed for 16 priority PAH concentrations using an accelerated solvent extractor. PAH distribution and source determination were conducted using spatial analysis and isomer ratios. All sample sites detected PAHs in soil, with the total mass ranging from 0.75 to 69.9 ng/g, which were predominantly four-ring structured PAHs. Total PAH concentrations were highest on the northeastern border of the neighborhood, whereas lower overall concentrations of PAHs were found on the southwestern border, at the highest elevation in the watershed. The ratio indeno[1,,3-cd]pyrene (IP) to indeno[1,,3-cd]pyrene plus benzo[ghi]perylene indicated vehicular combustion as the primary source in 19 of 23 samples. After heavy rainfall from Hurricane Harvey in the Manchester neighborhood, PAHs in soil were unevenly distributed throughout the neighborhood, with an accumulation of PAHs in the northeastern edges. Using isomer ratios and spatial analysis, the likely source of PAHs is from use of transportation infrastructure.

Domestic Exposures to Polycyclic Aromatic Hydrocarbons in a Houston, Texas, Environmental Justice Neighborhood.

Polycyclic aromatic hydrocarbons (PAHs) are a class of >100 chemicals that naturally occur in coal tar, crude oil, and gasoline and can be manufactured as part of dyes, plastics, and pesticides. PAHs are complex environmental toxicants and exposure to them have been linked to adverse health outcomes including cancer, as well as diseases of the skin, liver, and immune system. Residents of the environmental justice neighborhood of Manchester, located on Houston's East End, are disproportionally exposed to toxic pollutants from both industry and transportation infrastructure. Based on a longstanding community engagement partnership with the research team, neighborhood residents sought to better understand their domestic exposure to PAHs. Particulate wipes were used to collect dust from a marked area within the entryway of randomly selected homes to assess for the presence of PAHs. Nineteen of the 61 PAH analytes, including the Environmental Protection Administration's 16 priority PAHs and the subgroup of 7 probable human carcinogens, were found in the sampled homes. Residents of the Houston neighborhood of Manchester potentially have significant domestic exposure to PAHs from combustion sources. More research is needed to assess the source of the PAHs and to better understand the potential health impacts of these exposures.

Comparing residential contamination in a Houston environmental justice neighborhood before and after Hurricane Harvey.

INTRODUCTION: Polycyclic aromatic hydrocarbons (PAHs) are complex environmental toxicants. Exposure to them has been linked to adverse health outcomes including cancer, as well as diseases of the skin, liver, and immune system. Based on an ongoing community engagement partnership with stakeholder groups and residents, we conducted a small longitudinal study to assess domestic exposure to PAHs among residents of Manchester, an environmental justice neighborhood located in the East End of Houston, TX. METHODS: In December, 2016, we used fiber wipes to collect samples of household dust from 25 homes in Manchester. Following Hurricane Harvey, in September 2017, we revisited 24 of the 25 homes to collect soil samples from the front yards of the same homes. Wipes and soil were analyzed for the presence of PAHs using gas chromatography-mass spectrometry (GC-MS) methods. Principal component analysis plots, heatmaps, and PAH ratios were used to compare pre- and post-Hurricane Harvey samples. RESULTS: While direct comparison is not possible, we present three methods for comparing PAHs found in pre-hurricane fiber wipes and post-hurricane soil samples. The methods demonstrate that the PAHs found before and after Hurricane Harvey are likely from similar sources and that those sources are most likely to be associated with combustion. We also found evidence of redistribution of PAHs due to extreme flooding associated with Hurricane Harvey. DISCUSSION: Residents of the Manchester neighborhood of Houston, TX, are exposed to a range of PAHs in household dust and outdoor soil. While it was not possible to compare directly, we were able to use several methods to assess detected concentrations, changes in site-specific PAH allocations, and PAH origination. Additional research is needed to identify specific sources of domestic PAH exposure in these communities and continued work involving community members and policy makers should aim to develop interventions to reduce domestic exposure to and prevent negative health outcomes from PAHs.

Influence of hyperoxia on diastolic myocardial and arterial endothelial function.

OBJECTIVE: Hyperoxia is known to influence cardiovascular and endothelial function, but it is unknown if there are differences between younger and older persons. The aim of this study was to monitor changes in myocardial diastolic function and flow-mediated dilatation (FMD) in younger and elderly volunteers, before and after exposure to relevant hyperbaric hyperoxia. METHODS: 51 male patients were separated into two groups for this study. Volunteers in Group 1 (n=28, mean age 26 ±6, "juniors") and Group 2 (n=23, mean age 53 ±9, "seniors") received standard HBO2 protocol (240kPa oxygen). Directly before and after hyperoxic exposure in a hyperbaric chamber we took blood samples (BNP, hs-troponin-t), assessed the FMD and echocardiographic parameters with focus on diastolic function. RESULTS: After hyperoxia we observed a high significant decrease in heart rate and systolic/diastolic FMD. Diastolic function varied in both groups: E/A ratio showed a statistically significant increase in Group 1 and remained unchanged in Group 2. E/e' ratio showed a slight but significant increase in Group 1, whereas e'/a' ratio increased in both groups. Deceleration time increased significantly in all volunteers. Isovolumetric relaxation time remained unchanged and ejection fraction showed a decrease only in Group 2. There were no changes in levels of BNP and hs-troponin-t in either group. CONCLUSION: Hyperoxia seems to influence endothelial function differently in juniors and seniors: FMD decreases more in seniors, possibly attributable to pre-existing reduced vascular compliance. Hyperoxia-induced bradycardia induced a more pronounced improvement in diastolic function in juniors. The ability of Group 1 to cope with hyperoxia-induced effects did not work in the same manner as with Group 2.

Impact of oral vitamin C on histamine levels and seasickness.

BACKGROUND: Seasickness is a risk aboard a ship. Histamine is postulated as a causative agent, inversely related to the intake of vitamin C. Persons with mastocytosis experienced improvement of nausea after the intake of vitamin C. OBJECTIVE: To determine whether vitamin C suppresses nausea in 70 volunteers who spent 20 minutes in a life raft, exposed to one-meter-high waves in an indoor pool. METHOD: Double-blind placebo-controlled crossover study. Two grams of vitamin C or placebo was taken one hour before exposure. Blood samples were taken one hour before and after exposure to determine histamine, diamine oxidase, tryptase, and vitamin C levels. Symptom scores were noted on a visual analog scale. On the second day the test persons were asked which day they had felt better. RESULTS: Seven persons without symptoms were excluded from the analysis. Test persons had less severe symptoms after the intake of vitamin C (p < 0.01). Scores on the visual analog scale were in favor of vitamin C, but the difference was not significant. Twenty-three of 63 persons wished to leave the raft earlier: 17 after the intake of placebo and 6 after the intake of vitamin C (p < 0.03). Women (p < 0.02) and men below 27 years of age (p < 0.02) had less pronounced symptoms after the intake of vitamin C. Histamine (p < 0.01) and DAO levels were increased after the intake of vitamin C (p < 0.001) and after placebo (n.s.). The fact that the second test day was rated less stressful by most volunteers is indicative of habituation. CONCLUSIONS: Some of the data show that vitamin C is effective in suppressing symptoms of seasickness, particularly in women and men younger than 27 years of age, and is devoid of side effects. Histamine levels were initially increased after the test persons had been exposed to waves.

Dose-time dependency of hyperbaric hyperoxia-induced DNA strand breaks in human immune cells visualized with the comet assay.

PURPOSE: Hyperbaric oxygen exposure may induce dose-dependent DNA damage in peripheral blood mononuclear cells (PBMCs), and repetitive exposures of man may have protective cellular effects. METHOD: PBMCs, freshly isolated from non-divers and pure oxygen divers, were exposed to ambient air (21kPa) and hyperoxia at different levels: 100kPa, 240kPa, 400kPa and 600kPa) for up to 6.5 hours in an experimental pressure chamber. DNA double-strand breaks were studied in the comet assay by calculating the "tail moment" and an alternative "Yes or No" method for damaged nuclei. Previously, the experimental procedure had been optimized for human cell experiments: Pre-tests assured that DNA damage could be considered to be oxygen-induced; and cell viability remained over 95% during exposure time. RESULTS: Visible DNA damage increased with the partial pressure of oxygen (pO2) and exposure time dose-dependently. Linear regressions revealed r2 between 0.61 and 0.98 with the Yes/No method, and significant differences in slopes from control. Tail moment showed similar results, but with less accuracy. The PBMCs of oxygen divers exposed to 400kPa pO2 (up to six hours) showed a significant lower slope in the linear regression. CONCLUSION: Oxygen induces dose-dependent DNA double-strand breaks, and the Yes/No discrimination is superior to the tail moment in linearity and accuracy. Oxygen diver PBMCs seem to be more resistant to hyperbaric oxygen.