key: cord-0802556-o4pt9hs6
authors: Chaufan, C.; Dutescu, I. A.; Fekre, H.; Marzabadi, S.; Noh, K. J.
title: The military as a neglected pathogen transmitter and its implications for COVID-19: A systematic review
date: 2021-10-12
journal: nan
DOI: 10.1101/2021.10.09.21264758
sha: 77047d316b3f3f0b7f561bf8ecfb5ef77de0d39e
doc_id: 802556
cord_uid: o4pt9hs6

Background: The risk of outbreaks escalating into pandemics has soared with globalization. Therefore, understanding transmission mechanisms of infectious diseases has become critical to formulating global public health policy. This systematic review assessed the evidence for the military as a disease vector, an historically relevant one, yet overlooked in times of COVID-19. Methods: We searched 3 electronic databases without temporal restrictions. We identified 2010 of 6477 studies spanning over two centuries (1810 - 2020) that met our inclusion criteria and provided evidence for the military as a pathogen transmitter, within itself or between it and civilians. Two researchers independently extracted study data using a standardized form. Through team discussions, studies were grouped according to their type of transmission mechanism and direct quotes were extracted to generate themes and sub-themes. A content analysis was later performed and frequency distributions for each theme were generated. Results: Biological mechanisms driving transmission included person-to-person transmission, contaminated food and water, vector-borne, and airborne routes. Social mechanisms facilitating transmission included crowded living spaces, unhygienic conditions, strenuous working, training conditions, absent or inadequate vaccination programs, pressure from military leadership, poor compliance with public health advice, contractor mismanagement, high-risk behaviours, and occupation-specific freedom of movement. Contaminated food and/or water was the most common biological transmission route. Living conditions were the most common social transmission mechanism, with young, low ranking military personnel repeatedly reported as the most affected group. Certain social mechanisms, such as employment-related freedom of movement, were unique to the military as a social institution. While few studies explicitly studied civilian populations, considerably more contained information that implied that civilians were likely impacted by outbreaks described in the military. Conclusions: Features of the military identified in this study pose a significant public health threat, especially to countries with substantial military presence or underdeveloped health systems. Many social transmission mechanisms, unlike biological ones, were unique to the military, facilitating large-spreader events and affecting civilian health. As an increasingly interconnected world faces the challenges of COVID-19 and future infectious diseases, the identified features of the military may exacerbate current and similar challenges and impair attempts to implement successful and equitable pandemic policies.

In an increasingly interconnected world, understanding the transmission mechanisms of emerging viruses, as well as vulnerabilities and gaps in current public health measures, is crucial to developing effective and equitable public health policy.

Initial restrictions on the movement of populations contributed to flattening the global disease curve of COVID-19. 1 Overtime, widespread repurposing of existing drugs have led to important drops in morbidity and mortality, 2,3,4 a better understanding of the pathophysiology of COVID-19 is helping to stratify and individualize treatment strategies, 5 and vaccine developments are . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021. 10 .09.21264758 doi: medRxiv preprint providing hope. However, one key transmission vector has been overlooked by government officials, policymakers, and scientists alike in their responses to the pandemic: the role of the military as a disease vector. Its underreporting notwithstanding, there is well documented evidence, spanning over a century, for the military as a pathogen transmitter. 6 For example, the so-called Spanish Flu infected around 500 million people, one third of the world's population at the time, killing at least 50 million -by some counts around 100 million. Despite its name, recent historiography suggests that this pandemic originated not in Spain but in the United States of the highest rates of STDs, likely due to the young age of service members. 9 Military recruits are also at high risk of meningococcal disease, 10 a life-threatening infection associated with longterm sequelae, associated with risk factors such as young age, high carriage rates due to crowded living quarters, and global deployment to disease endemic regions. In sum, numerous historical and ongoing outbreaks of infectious diseases have been documented among military personnel.

Considering the dearth of attention to the role of the military as a pathogen transmitter in public health policy formulation, the goal of this systematic review has been to identify circumstances . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) 

Our study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines 11 for conducting reviews in healthcare. The protocol was registered with the International Prospective Register of Systematic Review (PROSPERO) (registration number: CRD42020188699).

Our overarching research question was: "What are the biosocial mechanisms whereby disease transmission occurs within the military and between military and civilian populations?" On May 13, 2020, we conducted a search in 3 electronic databases (Ovid MEDLINE, Ovid EMBASE, and Web of Science) using combinations of Medical Subject Headings (MeSH) and keyword search terms with no temporal restrictions. Key words included "military", "army", "troops", "navy", "naval base", "soldier", "disease vector", "disease carrier", "disease transmission", "pathogen transmission", "epidemic", "outbreak", "infect", "civilian" (full search strategy available under "supplementary materials"). We supplemented our database search by scanning the reference lists of included studies. Because an important aim of our study was to understand the role of the military in the COVID-19 pandemic, we also manually searched the grey literature . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) 

We included original research studies if they (1) were peer-reviewed and (2) provided evidence or supporting information for the military as a disease vector, or for military missions as highrisk environments/settings for the spread of infectious diseases, or (3) provided evidence for the spread of disease within the military, or (4) provided evidence for the spread of disease between military and civilian populations. We excluded articles if they (1) were not in English, (2) were reviews, case studies, letters, conference abstracts, editorials, commentaries, or surveillance reports, (3) did not describe/explain features of the military that promoted the spread of infectious disease or (4) did not use human participants. Authors independently screened each study in two separate rounds of study selection, a first consisting of title and abstract screening and a second consisting of full text screening. Disagreements were resolved by consensus.

We used a pre-formatted Excel worksheet (Microsoft, Redmond, Washington, USA) to extract data from studies meeting inclusion criteria. Extracted data included information such as study characteristics (e.g., study type), data collection methods (e.g., survey), sample size and participant composition (e.g., military vs civilian), associated countries (e.g., country of military origin), disease incidence characteristics (e.g., total cases, proportions among subgroups), and disease transmission characteristics (e.g., biological vs social mechanisms). We could not report . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint on the significance of different factors and/or population attributes on disease incidence, since many articles either included participants who had to report for duty at a different military base so left the study setting before completion, or only included symptomatic patients as participants and therefore could not provide a true incidence of disease in the studied population.

We applied an inductive narrative synthesis approach combining content analysis and thematic analysis to assess, summarize, and appraise findings that addressed our research question. 12 Upon identifying biological mechanisms of transmission, we grouped studies according to their social mechanisms of transmission by extracting quotes to identify themes and sub-themes. To demonstrate strength of support, we generated frequency distributions of themes and subthemes. 12 Because there is no consensus on best methodology in qualitative review syntheses for appraising a large dataset with significant variability in study designs, data collection methods, and study outcomes, we assumed trustworthiness on the basis of generally accepted standards of trustworthiness in qualitative research -credibility, dependability, confirmability, transferability; and authenticity. 13

Our search identified 6477 articles. After removing duplicates and non-English records, 3597 articles remained for screening. Upon title and abstract screening, we excluded 2651 articles, . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint which left 946 for full-text review, based on which we excluded 738 articles, thus leaving 208 that met our inclusion criteria. Our grey literature search yielded 2 additional articles on COVID-19 in the military. Our inter-rater reliability for article screening was 82%. Figure CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021.

Data collection methods varied, with many studies employing more than one (Table S1 ). Most studies (74%; 156/210) employed laboratory testing to identify outbreak causative agent(s) and determine disease incidence. Of 156 studies employing laboratory testing, the vast majority (87%; 136/156) tested to identify the disease agent and/or provide incidence rates (Table 1) 

The most common biological transmission mechanism identified was contaminated food/water, with 40% (84/210) of studies describing foodborne/waterborne-caused outbreaks. Other mechanisms were droplet-transmitted infections (35%; 73/210), sexually transmitted and bloodborne infections (14%; 30/210), vector-borne infections (14%; 29/210), airborne infections (7%; 15/210), and close contact infections (5%; 11/210). Some articles identified more than one biological transmission mechanism, so frequencies do not add up to the total number of articles.

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The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Table S2 in our supplementary materials for the specific list of countries included within each region. Pie chart (A) depicts the percent of studies taking place in each of the 6 regions. Pie chart (B) depicts the percent of studies with military groups originating from each of the 6 regions. Pie chart (C) depicts the percent of studies whose first author is affiliated with each of the 6 regions. Some articles took place in multiple regions, studied military groups originating from multiple regions, and/or the first author had multiple affiliations.

*Not Applicable refers to articles which did not include the military among their study populations.

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One hundred and eighty (86%; 180/210) articles reported on social mechanisms of disease transmission. Our thematic analysis identified twelve such mechanisms that we grouped under three categories: (1) policy (i.e., occupation-specific freedom of movement, vaccination programs), (2) institutional (i.e., contractor mismanagement, food contamination, living conditions, pressure from military leadership, poor infrastructure, poor public health management and services, training conditions, working conditions), and (3) individual (i.e., highrisk behaviours, ignoring public health advice). Because articles with quotes that corresponded to more than one social mechanism were counted as reporting on multiple mechanisms (Table S1) , social transmission mechanism frequencies do not add up to the total number of articles reporting on them (Table 2) .

Occupation-specific freedom of movement. Military personnel are very mobile: they are often required to complete training courses in foreign countries, deployed to foreign bases to fulfill missions, and travel to bases external from their home base. 14 New recruits regularly enter training bases as others who have completed training leave and personnel are often transferred from one base to another. 15 Deployed military personnel are not always subjected to similarly comprehensive population health assessments as non-mobile personnel. 16 Therefore military mobility contributes to spreading infections across populations, with 14% (26/180) of studies reporting on this social mechanism of transmission. Specifically, studies reported on military personnel assigned to complete multinational exercises, [17] [18] [19] with leave granted upon exercise . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Vaccination programs. Of the 180 studies identifying social mechanisms of transmission, 10% (18/180) reported suboptimal vaccination programs as contributing to disease incidence. Reasons reported included discontinuation of vaccines by suppliers during, or leading up to, the study period, 30 low vaccine supply during the study period, 31 or immunization not required for enrolment. 32 One study with two groups exposed to an infectious agent reported the outbreak almost entirely in the non-vaccinated group. 33 Of studies reporting absent or inadequate vaccination programs, 33% (6/18) described military populations with less than 35% of personnel vaccinated against the outbreak-causing disease.

Contractor mismanagement. A few articles (4%; 7/180) reported on 'contractor mismanagement', which we defined as any action performed by private contractors that may . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint negatively impact military health. We conceptualized these actions as social mechanisms of disease transmission and included actions such as unhygienic practices by cooks or food handlers contracted by the military, 34, 35 or military-contracted health professionals or food handlers who continued to work despite experiencing symptoms. 36 Food contamination. Although foodborne spread of disease is a biological mechanism of transmission, certain behaviours are required for food contamination. Around one tenth (11%; 19/180) of articles cited food preparation by unfit food handlers (e.g., working despite being symptomatic) 34 and consumption of food prepared with poorly handled ingredients (e.g., meat left unrefrigerated for long periods) 35,37 as frequently associated with illness.

Living conditions. Living conditions as a probable social mechanism of disease transmission were reported by a large minority of articles (42%; 76/180), including crowded living spaces, 24 found to be statistically significant for disease acquisition. Other usual but not statistically significant factors included exposure to animals 38 or insects and unhygienic living quarters. 39 Articles reporting on living conditions displayed a trend (18%; 14/76), whereby disease was more prevalent among younger, lower ranking and less educated military personnel. 27, 33, 40 Poor infrastructure. A minority of articles (16%; 28/180) reported on poor infrastructure as contributing to disease spread. The use of contaminated water by military personnel, especially if no other sources were available, was reported as associated with illness, 37,39 while many other articles reported it as a probable factor. 14, 18, 41, 42 Additionally, poor facilities, including unsanitary and/or unmaintained latrines, 43 unchlorinated or inadequately chlorinated water supply, 41 old and . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint corroded water pipelines, 42 inadequate ventilation, 30 poor air quality, 44 absence of essential appliances (e.g., no refrigeration facility, 43 no heating appliances 40 ) or an insufficient number of facilities 26, 27 were also reported as contributing factors to becoming ill.

Poor public health management and services. Although no article reported statistical significance between poor institutional management and/or services and disease incidence, about a fifth (20%; 36/180) reported probable associations related to this theme. Outbreaks also occurred in military bases with poor procedures, 17, 19, 23 including lack of testing before leaving and/or after arriving for deployment, 18 inadequate and/or obsolete supplies for use in military-serving water treatment plants, 37 delays in placing infected patients in isolation, 36,26 lack of enforced drug prophylaxis policy 45 , infected personnel allowed to leave the base whilst symptomatic, 14, 21, 30, 46 and personnel inadequately trained/educated and/or not equipped with the proper equipment/supplies for assigned tasks. 45, 47, 48 Additionally, a common contributing factor in training bases was penalizing trainees who missed training, for instance, by requiring them to restart training, with trainees reporting that they delayed or avoided seeking treatment despite experiencing symptoms. 38, 49 Pressure from military leadership. Very few articles (2%; 4/180) reported on the possible adverse effects of high-pressure often placed on military personnel -especially trainees -to report for duty: these articles reported that military personnel delayed or neglected to seek treatment due to a culture in the military against interrupting duties for medical reasons deemed of low to moderate severity. 17 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint Training conditions. Approximately one fourth of articles (24%; 43/180) reported on training conditions as a social mechanism of transmission. This mechanism is only applicable to the subset of articles taking place in training facilities (24%; 51/210), of which a majority (84%; 43/51) reported on it. Training assignments in remote and/or unmaintained areas (e.g., marshes) and participation in exercises with heavy physical components 22 were significantly associated with disease transmission. Specifically, travel to endemic areas, nocturnal exercises, low crawl training, sleeping in tents, poor nutrition and/or dehydration, and crowded training bases were identified among possible risk factors for infection. 50, 51 Working conditions. In close to a fourth (23%; 42/180) of articles, working conditions were reported as a social mechanism of disease spread. Specifically, crowdedness and being stationed near a stream or river, frequent troop movements, exhaustion, exposure to insects and livestock, and service in disease endemic areas were identified as risk factors. 29,37,38.44 Individual Ignoring public health advice. Military personnel and staff study participants in about one fifth (23%; 42/180) of articles were found to disregard public health advice. A significant association between lack of habitual handwashing prior to cooking by military food preparation staff and increased incidence of disease was reported by one article, 39 with many others indicating a likely correlation between poor hand hygiene practices and disease. 42 Similarly, another article found that prophylaxis non-compliance was significantly correlated with disease, 47 with numerous others identifying prophylaxis non-compliance as a probable factor. 22 Other behavioural factors . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint likely correlated with infection included lack of use of mosquito nets and approved-grade insect repellent sprays, and failure to wear permethrin-dipped and skin-covering clothing. 15 High-risk behaviour. Demographics and circumstances of military life make military personnel more likely to engage in high-risk behaviours than the general population. Personnel largely consists of young, single men and women who frequently leave their families for long periods for field operations. 52 Long absences from home tend to increase feelings of loneliness, which correlates with increased likelihood of engaging in risky behaviours (e.g., promiscuous sexual practices, substance abuse). 53 Although articles did not determine statistical significance between risk behaviours and disease, about one tenth (12%; 21/180) of articles discussing this social mechanism found that disease was more prevalent among individuals who engaged in unprotected sex, heavy smoking, or substance use, compared to those who did not.

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• Ability to leave base premises and/or country of military training despite outbreak or symptoms of disease. • Bypassing host country laws (e.g., criminal/ civil charge immunity, lack of airport screenings) due to a Status of Forces Agreement (SOFA), i.e., agreement between host nation and foreign nation outlining rights and privileges of foreign military personnel stationed in host nation.

Vaccination programs

• Exclusion of specific ranks from obtaining vaccinations;

• Limited supply of pharmaceuticals or vaccines; • Discontinuation of vaccines;

• Lack of vaccination program;

• Substandard expectations of immunization for incoming recruits.

• High population density within military bases, crowded barracks, crowded shared living spaces (e.g., dining halls, lavatories); • Rats, bats, or other vector carriers sharing living quarters; • Poor hygiene/sanitation conditions • Semi-open living environments allowing greater than usual freedom of movement; • Living conditions that promote presence of microorganisms.

Training conditions 1 • High-intensity military exercise contributing to increased mental and physical stress; • Military exercise increasing exposure to contaminated areas; • Training schedules (e.g., long hours, nocturnal activities) • Environmental conditions limiting access to resources (e.g., clean water, healthcare) or which adversely impact health (e.g., low air quality)

Working conditions 2

• Serving in endemic, rural, remote, or unmaintained areas; • Serving in environmental conditions which limit access to resources (e.g., clean water, healthcare) or which adversely impact health (e.g., low air quality); • Combat duty exposing personnel to greater risk (e.g., terrain, contact with combatants); • Requirement of frequent movement.

Poor public health management and services 36 (20) . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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• Lack of monitoring of compliance status with public health advice.

• Structural building problems, mould within living space(s), inadequate ventilation system(s) in buildings, poor facilities (e.g., lack of sufficient lavatories for the number of personnel in building, lack or insufficient access to clean drinking water).

Food contamination 3

• Inadequate or irresponsible hygiene practices leading to food/water contamination; • Inadequate medical attention for ill staff; • Infrastructure issues which lead to food contamination; • Delivery of contaminated food.

• Action(s) by outsourced company / individual that may adversely impact military personnel's health. 7 (4)

• Fear of disciplinary action for missing training or work to seek medical care; • Implicit expectation to continue duties despite feeling ill; • Explicit intimidation from superiors.

Ignoring public health advice • Non-compliance or poor adherence with protective health measures; • Delay or failure to seek medical care out of negligence or unspecified reasons.

• Substance abuse; • Unprotected sexual relations, sexual relations with commercial sex workers, visits to brothels or bawdy houses. 21 (12) . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ;

While our systematic database search did not identify articles with SARS-CoV-2 as the infectious disease agent, our manual grey literature search identified 2 such articles (< 1%; 2/210) meeting our inclusion criteria. 28 

Our systematic review confirms that multiple mechanisms drive disease transmission within military missions, bases, and medical institutions, into civilian populations. The most described biological mechanism was contaminated food/water; other mechanisms included sexually transmitted and bloodborne infections, close contact, vector-borne, droplet and airborne routes.

We also identified social mechanisms of transmission common to military life and work, such as crowded living, sleeping, and training practices, unhygienic living and/or food preparation conditions, strenuous working/training conditions, high-risk behaviours, absent/inadequate vaccination programs, poor compliance with public health advice, and contractor mismanagement. Some of these social mechanisms were unique to the military, such as pressure from military leadership to prioritize military goals over public health safety, and occupation-. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint specific freedom of movement. We also found that these social mechanisms have been occurring in military environments as early as 1810. 55 We posit that they continue into the 21 st century in military environments despite knowledge of disease containment measures because, at least in some cases (e.g., occupation-specific freedom of movement), they are accepted as necessary to is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted October 12, 2021. ; https://doi.org/10.1101/2021.10.09.21264758 doi: medRxiv preprint reviewed literature are quickly accumulating in the current COVID-19 era: for instance, in a period of less than three weeks, more than 40 US Navy warships had at least one sailor test positive. 56 

Our review has limitations: we could not calculate disease incidences among study populations because military personnel participants were often transferred, granted leave, or completed training prior to study completion, so participants were lost to follow-up. Therefore, even for studies reporting incidence rates (Table S1 ), these were likely underreported. Additionally, incidence rates may also be skewed because authors only obtained samples for laboratory testing from very small subsets of populations in a military base or restricted participation to symptomatic subjects. Therefore, the sample size from which incidence was determined was frequently not representative of the actual phenomenon of interest, i.e., disease incidence.

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Not applicable.

All data generated or analysed during this study are available within the article and its supplementary information files.

This research was partially funded by grant #439784 from the Canadian Institute for Health

Opportunity (2020-02-18).

CC conceptualized and designed the study, registered the review in PROSPERO, conducted the literature review, oversaw all steps of the study, initiated and led the writing of the manuscript, and secured funding for the project. IAD and HF assisted with the development of the study design, conducted searches, screened studies, extracted data from included studies, created tables and figures, drafted the appendices, and assisted with the drafting and multiple revisions of the manuscript. SM extracted data from included studies, assisted with drafting appendices, and reviewed and revised the manuscript. KJN co-originated the study idea, informed the literature review, and revised drafts. All authors approved the final manuscript as submitted.

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The first author wishes to thank her students and collaborators, who are a continuing source of inspiration for her work on global health policy and social justice. All authors wish to thank the School of Health Policy and Management for supporting collaborations between faculty members and emerging scholars.