Bridging the gap in genetics: a progressive model for primary to specialist care
The rapid expansion of genetic knowledge, and the implications for healthcare has resulted in an increased role for Primary Care Providers (PCPs) to incorporate genetics into their daily practice. The objective of this study was to explore the self-identified needs, including educational needs, of both urban and rural Primary Care Providers (PCPs) in order to provide genetic care to their patients.
Using a qualitative grounded theory approach, ten key informant interviews, and one urban and two rural PCP focus groups (FGs) (n = 19) were conducted. All PCPs practiced in Southeastern Ontario. Data was analyzed using a constant comparative method and thematic design. The data reported here represent a subset of a larger study.
Participants reported that PCPs have a responsibility to ensure patients receive genetic care. However, specific roles and responsibilities for that care were poorly defined. PCPs identified a need for further education and resources to enable them to provide care for individuals with genetic conditions. Based on the findings, a progressive stepped model that bridges primary and specialty genetic care was developed; the model ranged from PCPs identifying patients with genetic conditions that they could manage alone, to patients who they could manage with informal or electronic consultation to those who clearly required specialist referral.
PCPs identified a need to integrate genetics into primary care practice but they perceived barriers including a lack of knowledge and confidence, access to timely formal and informal consultation and clearly defined roles for themselves and specialists. To address gaps in PCP confidence in providing genetic care, interventions that are directed at accessible just-in-time support and consultation have the potential to empower PCPs to manage patients’ genetic conditions. Specific attention to content, timing, and accessibility of educational interventions is critical to address the needs of both urban and rural PCPs. A progressive framework for bridging primary to specialty care through a ‘stepped’ model for providing continuing medical education, and genetic care can was developed and can be used to guide future design and delivery of educational interventions and resources.
KeywordsPrimary care providers Genetics Genetic care Continuing medical education Undergraduate medical education Prevention
Health care administrator
Continuing medical education
Electronic medical record
Primary care provider
Public health medical doctor
The rapid expansion of genetics in medicine has resulted in an increased role for Primary Care Providers (PCPs), which could include family physicians, nurse practitioners and nurses, to assess and educate patients about genetic risks and realities. In this current study, however, the PCPs are family physicians. No longer limited to rare conditions, genetics is increasingly important in the diagnosis and management of common conditions such as diabetes, hypertension, cancer, heart disease, and stroke; conditions that are leading causes of death in Canada . With expanding clinical utility and demand for genetic care, including direct-to-consumer testing, PCPs [2, 3, 4] are increasingly called upon to integrate genetics into their practices [5, 6, 7, 8]. Although there is a general increase in awareness about genetics, there remains concern that PCPs do not receive sufficient training in clinical genetics, that medical school genetic education curriculae do not address the practicalities of primary care practice, and that continuing medical education (CME) efforts have had a limited impact [9, 10]. The ability for PCPs to include genetics in their practice is especially relevant given the limited number of trained genetics professionals (Canadian Medical Association [Internet]), (Shuman, Personal Communications, August 9, 2017).
PCP perspectives of genetics have been explored over the past two decades in various countries and medical systems [3, 4, 8, 11, 12, 13, 14, 15]. Previous studies have demonstrated that PCPs perceived themselves to lack knowledge and understanding of genetics , and the confidence and resources required to implement genetic care into clinical practice [3, 5, 6, 7, 8, 11, 12, 13, 14, 16, 17]. Thus, genetics in clinical practice trails behind scientific and technological advances, which has the potential to impede management of patients and their families. Specific issues identified included a need for more knowledge about the modes of inheritance, environmental and genetic factors [5, 6, 18], the role of genetics in common disorders , and the type of information available . PCPs indicated that they would benefit from more training in (i) linking family histories to risk assessments [4, 5, 6, 7, 15, 16, 18], (ii) communicating and counselling patients about genetics (e.g. managing family dynamics and facilitating informed decision-making in a way that reduces fears and/or concerns, and helps guide patients through complex issues) [6, 14, 18, 19, 20, 21], and (iii) knowing when and how to refer patients to a genetic specialist [3, 4, 5, 12, 16, 18]. Evidence suggests that PCPs would benefit from a better understanding about the options for early detection of disease, what genetic tests exist, how to interpret results, and prevention, management, and treatment strategies after a diagnosis [14, 15, 18]. For health care providers to be able to respond to the rapid increase in understanding about how genetic make-up shapes health and illness, medical education needs to transition from a traditional focus on the basic science of genetics to include a more clinical perspective [22, 23, 24]. PCPs suggested that this information is best taught through integrating genetics into existing pre-service medical education [14, 18] with CME used to educate current practitioners. Optimal CME programs would be accessible, short, engaging, timely, and either free or incentive-based [5, 14]. PCPs emphasized that education should incorporate a case-based practical approach, include information on clinical applications, focus on strategies to improve patient outcomes and practice (e.g., blended learning courses, online modules, PCP involvement in face-to-face or virtual genetics appointments), and be relevant to day-to-day clinical practice [4, 5, 7, 14, 25, 26, 27, 28, 29, 30].
In spite of efforts to date, PCPs continue to express concern about inadequate knowledge, confidence, and resources, given the increasing role that genetics is expected to play in primary care . Therefore, an up to date needs assessment of primary care providers is timely with a specific emphasis on genetic education needs. The objective of this study is to explore the self-identified genetic needs of PCPs, with specific consideration paid to the unique needs of both urban and rural PCPs. To date, few studies have explicitly considered the impact of practice locale on the availability of genetic education, whereas this study incorporates the perspectives of both urban and rural practitioners.
A qualitative grounded theory approach was used . Ten key informant interviews (n = 10) and three PCP focus groups (FGs) (n = 19) were conducted.The interview results were used to develop the FG protocol. The FGs explored PCPs perceptions of their current and future roles in providing genetic care, and the effectiveness of their genetic education, educational preferences, and perceived needs for improving future educational strategies. All interviews and FGs were audio-recorded and transcribed verbatim. Participants were de-identified to ensure confidentiality. All participants were given pseudonyms by assigning them a number for the key informant interview (I) or PCP focus group (FG). For example, informant number one was identified as (Informant 1), whereas, a PCP in FG one was identified as (FG1). The informants were also identified by their professional role (e.g., Informant 8GC refers to Informant Number 8 who is a genetic counsellor). NVivo 10 was used to store and manage the data. This study reports a subset of data from a larger study about genetics in primary care . Ethics compliance was received from the Queen’s University Health Sciences and Affiliated Teaching Hospitals Research Ethics Board (File # 6005987).
Key informant interviews
Stratified purposive sampling was used to recruit key informants to ensure a cross-section of perspectives and experiences. The key informants were selected by the research team and included one health care administrator (A), one clinical geneticist (CG), one nurse practitioner (NP), one public health medical doctor (PH/MD), two genetic counsellors (GC), and four primary care medical doctors (MD). Interview protocols were revised using an iterative approach as new themes emerged. All interviews were conducted by a distanced Research Assistant (RA) who had no prior involvement with the genetics program. To ensure authenticity of the data, member-checking was offered to all and completed by 4/10 participants. Each interview took approximately 45 min. Analysis of the interviews informed the development of the FG script.
Participants for the three FGs were selected using purposive homogeneous group sampling to include only family physicians practicing in Southeastern Ontario (SEO). The Family Health Teams (FHT) in the region were contacted by the RA, and each local FHT administrator extended invitations to PCPs on their team and in the area. One FG consisted of urban PCPs (n = 5), while two FGs consisted of rural PCPs (n = 14). FGs were facilitated by a different distanced RA than the RA who held the interviews, and the Principal Investigator (PI) recorded field notes. The RA was selected for experience in facilitating FGs and had no prior involvement with genetics or with the PI. The FGs identified additional themes. Saturation of the data was reached with three focus groups. FGs took approximately one hour.
Themes and sub-themes captured in interviews and focus groups
1. Roles and responsibilities of PCPs
Current demand exceeds supply of specialists; increased patient requests for education and testing
2. Genetic education needs
Managing patient care
3. Genetic education strategies to meet PCP needs
Medical education needs additional focus on clinical genetics
4. General considerations
Awareness of educational opportunities
Amount of knowledge necessary/appropriate for Primary Care Providers
Ten key informant interviews (n = 10) and three PCP focus groups (FGs) (n = 19) were conducted, over 18 months. All participants worked in SEO. The PCPs in the interviews and FGs were between the ages of 30 and 60 years, and included men and women who had been in practice for a minimum of five years.
Participants acknowledged that PCPs have a responsibility to ensure patients receive genetic care. However, opinions were inconsistent about who would provide which type of genetic care. To ensure they provided appropriate care and referrals, PCPs believed that they required additional education. Participants highlighted educational strategies from which they would benefit and noted considerations that should be made when planning educational interventions. Table 1 identifies the four themes and 11 sub-themes that emerged from the data.
Theme 1: roles and responsibilities of PCPs
Overall, most participants recognized that as the demand for genetic testing and care increases, this demand will exceed the supply of specialists. For example, one participant stated, “I don’t know one single medical geneticist that is not overrun with work and I just can’t see how it’s going to get easier. I think it’s going to get much more difficult for them to facilitate their workload” (Informant 1GC). Another participant suggested that PCPs’ key role lies in “identification [of genetic conditions] and referral when appropriate, or [patient] education about the illness” (Informant 7MD).
“the kind of psychosocial support that they [can] provide to patients in a very general way… in any circumstance [it] is relevant to the kind of support that one provides to individuals with, or at risk of, an inherited disease.” (Informant 8CG)
Theme 2: genetic education needs
Most participants identified a need for education that would specifically guide decision-making processes about referrals. As one PCP stated, “I would have to do some research on their [patients’] behalf to figure out what my role is next; if I refer to genetics, if I refer to a specialist, and if it’s necessary” (FG1).
“You have to be pretty up to date on the evidence available to really do proper counselling and make recommendations especially if people are coming to you saying 'what should I do now’. Instead of giving them options, if you’re making specific recommendations then you need to be pretty comfortable with your level of knowledge and that it’s up to date.” (FG3)
In acknowledging the value of genetic specialty expertise, one PCP stated:
“I think that’s the biggest thing, having more information when they send me the referrals... for a better ability to do triage…you can’t just send the referral form that says, please see this person.” (Informant 3GC)
“I’ve been always very pleased when we refer someone for genetic counselling… and some expert spends time with the patient, gives them a ton of information and sends me a three-page letter at which I’m always amazed…. I know… [a] moderately small amount…. It would be nice to have something in the middle…. I sometimes think, this problem that [the patient is] concerned about is too small for the full genetic interview with a real expert, but I don’t know enough to give them something between the full consultation and my limited knowledge.” (FG2)
When PCPs determined a referral was not necessary, most stated that they would benefit from increased education about how to provide genetic care within their practice. It was suggested that knowledge should be, “enough… that you can appropriately counsel your patients” (Informant 2MD), and include the “positive and negative impacts the testing can have” (Informant 10PH/MD).
Theme 3: genetic education strategies
Participants identified a range of strategies and suggestions for education that they perceived as being particularly beneficial for them to enhance their ability to incorporate genetics into their practices. One participant states quite succinctly: “The reality of any medicine is you’re always learning new stuff. And that would be the main thing I think for family docs is finding a way to keep up with specific knowledge based aspects of genetics” (Informant 2MD).
Some participants suggested that undergraduate medical education should incorporate genetics into an array of subject areas, refrain from discussing it only in the context of rare conditions, and ensure consistency across medical schools. The educational challenge, however, continues to include strategies to enable health care providers to remain current in the rapidly evolving knowledge-base within genetics. Some participants suggested that undergraduate medical education provided adequate education but, due to the rapid growth in the field of genetics, knowledge obtained in medical school quickly becomes outdated: “So I think in medical school and residency – the training we were provided with was up-to-date at that point. But it is not up-to-date any longer, depending on when they trained” (Informant 10PH/MD).
Participants indicated that the continual need for genetics education could be accomplished both formally and informally. Formal educational strategies included continuing medical education (CME), lectures, seminars, or conferences—all with a focus on case-based learning. Participants discussed a range of CME options, with one saying, “I personally like the CME format because it gets me there and it gets my full attention and there’s opportunity to interact” (FG1). Others agreed that the “most useful things are the good old fashioned face to face seminar[s]… the best way to educate family doctors is to come and give them re-education sessions... Come to the hospitals and the seminars and rounds” (Informant 9PH/MD), or perhaps “a half day conference just in genetics” (Informant 7MD). Regardless of format, some participants suggested that, “case-based learning actually would be the most helpful. Because… when you see a case and you learn about it, that’s when you remember it” (FG3).
Like this respondent, many participants discussed the importance of electronic resources. They found value in electronic resources that could be quickly accessed when searching for information in specific cases:
“You’d have these hallway consultations with somebody … it was just a fantastic – he was the best resource. He was around most days and you’d run into him and you had this specific clinical scenario involving this individual patient. And you can’t really find the answer in books because this patient had a peculiar set of co-morbidities that made their answer really the only answer. And I think that whole idea of the ability to access some sensible expert to give you timely advice in a fairly, a user friendly way would be a superb tool. Not just for genetics but for everything–call this world medicine, e-curb site consult.” (FG2)
“Websites where they can easily obtain the information and access what the next best steps should be.” (Informant 5MD)
Some participants discussed the benefits of an automated notification in the electronic medical record (EMR) which highlighted the need for genetic testing such that,
“FAQ on genetics set up for family doctors… [with] answers to] basic questions, ‘Should I refer this person for breast cancer screening or whatever else? Yes or no.’ A little blurb on the evidence. And then a little thing down below saying – if you’re still having problems contact us. And you [could] fill your question and fire it off.” (FG2)
“If you entered, ‘three people in the family who had breast cancer’ for example… not only [are you] entering the data in to figure out the risk... but inadvertently… you don’t even realize… that might be something that should trigger a genetics referral or another test… the EMR [asks] ‘have you considered ____ because you’ve entered three people with breast cancer in this person’s family history’… it prompts.” (Informant 2MD)
Theme 4: general considerations
Rural practitioners acknowledged specific challenges that distance could pose for receiving adequate genetics CME. One participant indicated that, “there is easier access to in-services and education presentations at the urban centres as opposed to the rural hospitals or the rural centres” (Informant 6A) while another stated that “an [urban] physician that has access to ongoing rounds at a major university centre may have a different level of exposure to genetics” (Informant 1GC). Finally, one participant reminded educators that the scope of PCP practice should be considered and that it should be acknowledged that PCPs cannot be expected to be genetic experts.
“In this day and age, when everyone’s busy – it makes a lot of sense to do these webinars and all this kind of stuff. I find I don’t participate in them nearly as much because there’s always something else pulling your attention.” (FG1)
“Remembering the details is not all that important as long as you remember that there is some aid. There is a piece of paper that [includes what] I need to know…about genetics that will give me some information about what to do with patients with genetic and sensitive issues. That’s the kind of superficial knowledge I think we need.” (FG1)
The advantage of this model is that it provides a developmental and sequential continuum of primary to tertiary care for increasingly complex cases. It also provides a framework to make the roles of different care providers more explicit. PCPs view their role as providing the care they feel capable of and determining which patients warrant a more detailed assessment. However, PCPs have often received little formal education in genetic medicine and have had limited exposure to the identification and management of patients with genetic conditions. Therefore, while PCPs feel a responsibility to provide genetic care to their patients, many discussed a lack of knowledge, confidence, and resources to do so and, therefore, are either not comfortable or limit the degree to which they integrate genetics into their daily clinical practice. In spite of efforts at CME, these findings are consistent with prior literature [3, 4, 5, 6, 12, 14, 16, 18, 20, 26].
Many PCPs expressed a concern that they were unsure when referral was appropriate, and expressed a need for education or a guide which can be used to help support decision-making surrounding referrals to genetics. PCPs want a contact they can e-mail or call to informally discuss a case to determine whether to refer or manage a patient themselves. We recommend a more explicit and accessible role for e-mail and e-consults as a corridor consultation method given that systems change is needed if PCPs are going to play a larger role in genetic care. For example, an approach to this e-consult model could be in the form of a single email address to which PCPs can direct their questions. Once the email is received by a centralized location, it is forwarded to an on-call genetics specialist who would respond within a specified timeframe. The specialist would assist the PCP in determining which step(s) would be most appropriate be it to assist in reassuring the patient, provide education, offer expert advice about the specific tests needed, or expedite a referral, as described in our ‘stepped model’. An electronic forum would also address some of the barriers outlined by rural PCPs. The challenge in implementing this approach to genetic care lies in PCP access to genetics colleagues/experts in a timely manner. In addition, in some jurisdictions, access to funding for genetic tests requires a geneticist consult.
To improve PCP confidence in meeting patients’ genetics needs, participants made specific recommendations. PCPs’ suggestion of improving undergraduate medical education in genetics through an integration across disciplines is consistent with other reports [14, 18]. Incorporation of genetics into Family Medicine residency programs was also considered important. Consistent with CME literature in general, PCPs discussed the need to improve formal CME opportunities and to utilize a case-based approach that connects theory to practice [14, 25]. In addition, participants also emphasized the value of informal learning that occurs through regular contact with other professionals, with a goal to avoid unnecessary referrals. For example, “just-in-time” consultations with experts or methods wherein a librarian is employed to help PCPs locate necessary diagnostic information, have been shown to improve the speed and quality of PCP decision making, subsequently having the potential to improve patient access to care .
Regardless of method, we found that participants highlight that when considering education specifically intended for PCPs, program developers and organizers must consider time constraints, the level of the learner, and understand that PCPs cannot be expected to be as knowledgeable as genetic experts , thus set realistic limits on what PCPs are expected to know. Timely access to information would also assist PCPs in effectively embedding genetic care into their practices . Education should be relevant to daily practice and include information on clinical application [5, 14, 26]. These PCP-focused educational aspects are supported in the literature, however, our results suggest that PCPs must be made explicitly aware of educational opportunities. Improved access to genetic education would allow other healthcare providers, such as nurses and nurse practitioners, to participate in assessing genetic risk factors that may include taking family histories and providing patients with education around their concerns.
Considerations for education of rural practitioners
Rural PCPs identify some specific concerns regarding access to education. Most importantly, they highlight that distance is a significant barrier to both formal and informal means of education . Lack of regular contact with larger academic centres, leads to fewer informal learning opportunities for rural PCPs compared to their urban counterparts [37, 38]. As programs are developed it is essential to include options (such as just-in-time e-mail access to an expert) that increase CME accessibility and informal interactions regardless of geographic location.
Limitations of study
This study was conducted in SE Ontario with a small number of PCPs and is, therefore, limited in terms of generalizability at a national and international level. However, we do believe that the progressive stepped model for bridging primary to specialty care can be adapted to specific contexts within a healthcare system and inform future CME interventions.
In summary, while PCPs identify a need to include genetics in their practices, they perceive that a lack of knowledge and resources is one of the major factors that impedes their ability to provide quality patient care in genetics. To address gaps in PCP knowledge, a diverse set of educational opportunities and interventions should be made available in order to meet the varying needs of different PCPs and include specific attention to content, timing, and accessibility.
The findings from this research are pertinent to the development of future educational opportunities and interventions. While educational interventions aimed at improving PCPs’ knowledge of genetic medicine may increase knowledge and perceived competence in genetic medicine, they are not always accompanied by a change in practice or referral patterns [39, 40, 41, 42]. The progressive stepped model of bridging primary and specialty care developed from this study has the potential to assist in bridging the gap between primary care and genetics expert settings. Supporting PCPs in the care of patients they are uncertain about can be addressed with just-in-time strategies including timely access to experts. With the current study and the previous literature in mind, future research should not only assess the educational merit of opportunities and interventions, but should also seek to assess to what extent, and in which situations PCPs support the integration of genetics into their practices. To optimize the future of genetic care, ongoing support is needed to facilitate greater informal as well as formal collaboration, including the sharing of knowledge and skills between PCPs and genetic specialists.
We would like to thank Jyoti Kotecha for co-ordinating the initial part of this project, and to Jane Yealland for conducting the focus groups. A special thanks goes to all the participants for making this work possible.
JM, CA, RB, GB, MF, JC, SP, and CW made substantial intellectual contributions to the research concept and design for the work. JM, LR, CW, BH and ND analyzed and interpreted the data. All listed authors contributed to writing the manuscript and providing final approval for the submitted manuscript. All authors read and approved the final manuscript.
This work was funded by the Clinical Teachers’ Association of Queen’s University (CTAQ) Endowment Fund. The role of the CTAQ was solely financial support, they were not involved in any aspect of the research.
Ethics approval and consent to participate
This study was approved by the Queen’s University and Affiliated Teaching Hospitals Health Sciences Research Ethics Board (File No. 6005987). Written, informed consent was obtained from all individual participants included in the study.
Consent for publication
All participants (through the written, informed signed consent) and authors have consented to have this work published. No patient populations were included in this study.
The authors declare that they have no competing interests.
- 1.Government of Canada SC. Health Fact Sheets. 2015. http://www.statcan.gc.ca/pub/82-625-x/2015001/article/14296-eng.htm. Accessed 28 Feb 2018.
- 3.Carroll JC, Brown JB, Blaine S, Glendon G, Pugh P, Medved W. Genetic susceptibility to cancer. Family physicians’ experience. Can Fam Physician. 2003;49:45–52.Google Scholar
- 5.Houwink EJ, van Luijk SJ, Henneman L, van der Vleuten C, Jan Dinant G, Cornel MC. Genetic educational needs and the role of genetics in primary care: a focus group study with multiple perspectives. BMC Fam Pract. 2011;12(5).Google Scholar
- 9.Bottorff JL, McCullum M, Balneaves LG, Esplen MJ, Carroll J, Kelly M, et al. Establishing roles in genetic nursing: interviews with Canadian nurses. Can J Nurs Res. 2005;37:96–115.Google Scholar
- 10.Harris R, Challen K, Benjamin C, Harris H. Genetic education for non-geneticist health professionals. Community Genet. 2006;9:224–6.Google Scholar
- 11.Harding B, Webber C, Ruhland L, Dalgarno N, Armour CM, Birtwhistle R, et al. Primary care providers’ lived experiences of genetics in practice. J Community Genet. 2018:1–9.Google Scholar
- 15.Bottorff JL, Blaine S, Carroll JC, Esplen MJ, Evans J, Nicolson Klimek ML, et al. The educational needs and professional roles of Canadian physicians and nurses regarding genetic testing and adult onset hereditary disease. Public Health Genomics. 2005;8:80–7.Google Scholar
- 19.Jaquez M, Haun R, Frye R, Frazer T. Teaching clinical genetics to pediatric residents in an outpatient setting: a proposed model. Genet Med. 1999;1:56–6.Google Scholar
- 20.Liaw S-T. Genetics and genomics in general practice. Aust Fam Physician. 2010;39:689–91.Google Scholar
- 21.Petrou M. Genetic counselling. In: Prevention of Thalassaemias and other haemoglobin disorders: volume 1: principles. 2nd Edition. Angastiniotis M, Eleftheriou A, Galanello R, et al., authors; Old J, editor. Nicosia, Cyprus: Thalassaemia International Federation; 2013. p. 161–165. http://www.ncbi.nlm.nih.gov/books/NBK190461/. Accessed 23 Feb 2016.
- 24.Schmidtke J, Paul Y, Nippert I. Education in medical genetics for physicians: Germany. Community Genet. 2006;9:235–9.Google Scholar
- 25.Blashki G. Primary care psychiatry: taking consultation–liaison psychiatry to the community. Australas Psychiatry. 2005;13:302–6.Google Scholar
- 28.Carroll JC, Makuwaza T, Manca DP, Sopcak N, Permaul JA, O’Brien MA, et al. Primary care providers’ experiences with and perceptions of personalized genomic medicine. Can Fam Physician. 2016;62:e626–35.Google Scholar
- 31.Creswell JW. Qualitative inquiry and research design: choosing among five approaches: SAGE Publications; 2012.Google Scholar
- 32.Creswell JW. Research design: qualitative, quantitative, and mixed methods approaches: SAGE Publications; 2013.Google Scholar
- 33.Glaser BG. Theoretical sensitivity: advances in the methodology of grounded theory. Sociology Pr. 1978.Google Scholar
- 34.Glaser BG, Strauss AL. The discovery of grounded theory: strategies for qualitative research. 4. Paperback printing. New Brunswick: Aldine; 2009.Google Scholar
- 35.Charmaz K. Constructing grounded theory (2nd Ed.). Thousand Oaks, California: Sage Publications; 2014.Google Scholar
- 39.Carroll JC, Wilson BJ, Allanson J, Grimshaw J, Blaine SM, Meschino WS, et al. GenetiKit: a randomized controlled trial to enhance delivery of genetics services by family physicians. Fam Pract. 2011.Google Scholar
- 42.Laberge AM, Fryer-Edwards K, Kyler P, Lloyd-Puryear MA, Burke W. Long-term outcomes of the “genetics in primary care” faculty development initiative. Fam Med. 2009;41:266–70.Google Scholar
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