Medicine is a science which is used by clinicians to heal patients. At the same time, the patients teach their doctors. Since directly contacting their patients, doctors may encounter with different unusual clinical presentations of common diseases or even common manifestations of rare diseases. These experiences have been expressed as case reports or case series as one of the teaching tools to assist young physicians and colleagues to apply the information for other patients who encounter with similar scenario. Today’s practicing medicine requires evidence-based medicine to be cooperated into medical practices and the majority of the evidences are resulted from more complex research study designs including analytic and experimental studies. However, it is common that the original idea or motivation to conduct these types of research studies are based on case reports or case series. Some may believe in hierarchical value of evidence with the lowest one are case reports or case series. Several aspects of case reports or case series and evidence-based medicine are different, but the goal of these are to enhance medical knowledge and subsequently improve patient care. Therefore, case reports and case series remain contributing to medical knowledge and even originate new knowledge. This editorial aims to emphasize several important aspects of case reports and case series from general sense for managing individual patient through their impacts on public health aspect.

Several scientific knowledge arise from observation of people and scientists. Sir Isaac Newton studied and worked on the theory of gravity from observing a fall of an apple [1]. Many invention came from inspiration. Wright brothers dreamed to fly after having a toy helicopter [2]. In addition, the previously unsuccessful experiments make scientists to further observe and research. Thomas Alva Edison who was not the first light bulb inventor, but was the first inventor of the light bulb, which can be used in a practical way, successfully invented a light bulb after several people failed to do so at that time [3].

Similar to any scientific fields, medical knowledge started from an observation from a single patient who has unusual presentations of common diseases or even usual presentations of uncommon conditions. Documentation and sharing experiences about the things that are still unclear lead the young generation to extend that knowledge to become more evidence and innovation.

Among non-experimental studies, case reports and case series are the most basic type of the study, but they are often the fundamental knowledge of all other types of non-experimental studies including case series, cross sectional, case-control, or cohort studies and experimental study like clinical trial [4] (Figure 1).

Nowadays, medical knowledge progresses continuously and rapidly. Medical research from different study designs including case reports and case series can bring different values to medical fields in different ways. The goal of these studies is to discover and add on to new medical knowledge. However, there are some different aspects that unique for each study design (Table 1).

All clinicians and healthcare providers practice and learn from their patients. Most clinicians consult their colleagues or specialists whenever they encounter with unclear clinical situations in terms of clinical manifestations, diagnosis, interpretation of laboratory data or investigation, and management particularly in the setting of rare conditions or diseases as well as rare manifestations in common diseases. Nevertheless, uncertainties sometimes remain. Previously published clinical case reports or case series are therefore other resource that are helpful to assist in their clinical decision making.

Not only the benefit of case reports to help in the management for a single patient, they also potentially extend the benefit to societies at large or even to public health. The recent example that emphasizes this benefit is Zika virus epidemic. A clinical case report [5][6] can lead to subsequent analytic studies to characterize clinical manifestations, investigations, transmission, and complications of Zika virus infection in human and further studies during Zika virus outbreak [7] [8][9][10][11][12][13] as well as discovery of management and prevention such as vaccine [14][15].

Several values of case reports and case series are not only contributing to the field of medicine, but also impacting or changing regulation or even public health policy. Particularly, the initial step of analytic research for drug safety often starts with case reports or case series [16]. This can be demonstrated by one of the new field of public health, pharmacoepidemiology involving in drug utilization, effectiveness, and safety. With so many innovative drugs, biological, biosimilars, or medical devices undergoing accelerated approval process, uncertainties and uncovered information particularly adverse drug experiences (ADE) or unintended side effects may arise. For instance, a report of new or unusual ADE can guide drug consumers, providers, manufacturers, and governmental organizations responsible to the regulation of drug utilization, effectiveness, and safety like Food and Drug Administration (FDA) to be alerted. This subsequently leads to further investigation, conducting research to prove the causal inference of the ADE and drug utilization. Ultimately, the action of these research leads to new regulation and management of the drug utilization for the public [17][18][19][20][21].

Therefore, case report and case series are actually the origin of several observational and experimental studies and can expand observation from characteristics of a single or multiple cases to more complex studies and eventually evidence-based knowledge, which can be applied for patient care through public health. The experiences from this application can subsequently lead to further observation of unknown knowledge requiring additional processes of obtaining knowledge from self-study, consultation, or research. This becomes a “cycle of medical knowledge” as demonstrated in the Figure 1.

Although several merits of case reports and case series, some disadvantages may take into the consideration when utilizing the information from case reports or case series mainly due to limitation of making causal inferences from a small number of studied patients (Table 2).

From the past, nowadays, and in the future, case reports and case series tell us the stories and clinical entities of rare conditions or diseases or rare presentations of the common diseases. They are also the foundation of many descriptive as well as analytic studies and eventually experimental trials. Case reports and case series can not only be a way to help and communicate other physicians and healthcare providers about unusual aspect of individual case or a small group of patients, but also a foundation of idea and motivation in conducting. In addition, case reports and case series are also another method to formally inform involved and responsible stakeholders to further examine and again conduct further more complex research studies to determine causal inferences and this subsequently leads to further action and regulation to ultimately improve patient care. Therefore, case reports and case series should remain one of the efficient tools to inform and educate our colleagues, extend further medical knowledge for patient care, and potentially involve in public health.

Keywords: Case reports, Case series, Modern evidence-based medicine, Pharmacoepidemiology, Public health

1. Fara P. That the apple fell and Newton invented the law of gravity, thus removing God from the cosmos. In: Numbers RL, Kampourakis K, editor. Newton's Apple and Other Myths about Science. USA: Harvard University Press; 2015. p. 48–56.    
2. Crouch TD. The Bishop’s Boys: A Life of Wilbur and Orville Wright. London: W. W. Norton & Company; 2003.    
3. https://www.biography.com/people/thomas-edison-9284349    
4. Nissen T, Wynn R. The clinical case report: A review of its merits and limitations. BMC Res Notes 2014 Apr 23;7:264.   [CrossRef]   [Pubmed]    
5. Macesic N, Abbott IJ, Johnson DF. Photo quiz: Fever and rash in a husband and wife returning from the cook Islands. Clin Infect Dis 2015 Nov 1;61(9):1445, 1485–6.   [CrossRef]   [Pubmed]    
6. Foy BD, Kobylinski KC, Chilson Foy JL, et al. Probable non-vector-borne transmission of Zika virus, Colorado, USA. Emerg Infect Dis 2011 May;17(5):880–2.   [CrossRef]   [Pubmed]    
7. Gourinat AC, O'Connor O, Calvez E, Goarant C, Dupont-Rouzeyrol M. Detection of Zika virus in urine. Emerg Infect Dis 2015 Jan;21(1):84–6.   [CrossRef]   [Pubmed]    
8. Schuler-Faccini L, Ribeiro EM, Feitosa IM, et al. Possible association between Zika Virus infection and microcephaly - Brazil, 2015. MMWR Morb Mortal Wkly Rep 2016 Jan 29;65(3):59–62.   [CrossRef]   [Pubmed]    
9. Rasmussen SA, Jamieson DJ, Honein MA, Petersen LR. Zika Virus and birth defects–reviewing the evidence for causality. N Engl J Med 2016 May 19;374(20):1981–7.   [CrossRef]   [Pubmed]    
10. Mlakar J, Korva M, Tul N, et al. Zika Virus associated with microcephaly. N Engl J Med 2016 Mar 10;374(10):951–8.   [CrossRef]   [Pubmed]    
11. Brasil P, Pereira JP Jr, Moreira ME, et al. Zika Virus infection in pregnant women in Rio de Janeiro. N Engl J Med 2016 Dec 15;375(24):2321–34.   [CrossRef]   [Pubmed]    
12. de Araújo TV, Rodrigues LC, de Alencar Ximenes RA, et al. Association between Zika virus infection and microcephaly in Brazil, January to May, 2016: Preliminary report of a case-control study. Lancet Infect Dis 2016 Dec;16(12):1356–63.   [CrossRef]   [Pubmed]    
13. Bautista LE, Sethi AK. Association between guillain-barré syndrome and Zika virus infection. Lancet 2016 Jun 25;387(10038):2599–600.   [CrossRef]   [Pubmed]    
14. Larocca RA, Abbink P, Peron JP, et al. Vaccine protection against Zika virus from Brazil. Nature 2016 Aug 25;536(7617):474–8.   [CrossRef]   [Pubmed]    
15. Dowd KA, Ko SY, Morabito KM, et al. Rapid development of a DNA vaccine for Zika virus. Science 2016 Oct 14;354(6309):237–240.   [CrossRef]   [Pubmed]    
16. Abou Chakra CN, Pariente A, Pinet M, Nkeng L, Moore N, Moride Y. Case series in drug safety: A review to determine characteristics and quality. Drug Saf 2010 Dec 1;33(12):1081–8.   [CrossRef]   [Pubmed]    
17. http://www.fda.gov/downloads/ RegulatoryInformation/Guidances/UCM126834.pdf    
18. Vandenbroucke JP. Case reports in an evidence-based world. J R Soc Med 1999 Apr;92(4):159–63.   [Pubmed]    
19. Haven KF. Marvels of Science: 50 Fascinating 5-Minute Reads. Littleton, Colorado: Libraries Unlimited. 1994. p. 182.    
20. Hill AB. The Environment and Disease: Association or Causation? Proc R Soc Med 1965 May;58:295–300.   [Pubmed]    
21. Charlton BG, Walston F. Individual case studies in clinical research. J Eval Clin Pract 1998 May;4(2):147–55. 10.1046/j.1365-2753.1998.00011.x   [CrossRef]   [Pubmed]