Contact between people plays an instrumental role in the direct spread of infectious diseases. Human contact patterns are fundamental to our understanding of the dynamics of infectious disease spread [1
]. Put simply, an infectious disease that spreads from person to person cannot persist unless an infected person meets a susceptible one [1
]. In terms of pathogens, this means that an infection that is readily spread through daily social contact does not have to last long, since an infectious person is almost certain to meet a susceptible individual within 1 day or 2 days [1
]. It is not possible for each member of the population to have the same chance of meeting everyone else; instead, individuals are likely to have varying patterns of contact with one another. To gain a better understanding of the epidemiology of infectious diseases, we need to study these contact patterns, as they are important determinants of the spread of infectious disease. Moreover, the ability to predict infectious disease spread and the impact of interventions such as vaccinations depends on whether close contacts among individuals can be quantified. Understanding the nature of human contact patterns is crucial for predicting the impact of future pandemics and for devising effective control measures [2
]. Presently, reporting systems in many countries measure the numbers and characteristics of contact patterns in the population with the goal of controlling the spread of infection [4
]. Moreover, mathematical modeling of infectious diseases transmitted by respiratory or close-contact routes (e.g., pandemic influenza) is being increasingly used to predict epidemics and to determine the impact of possible interventions [5
In 2015, an outbreak of Middle East Respiratory Syndrome (MERS) occurred in Korea. From the first case on May 20, 2015 to the official declaration of the cessation of MERS on December 23, 2015, a total of 186 cases were recorded; 38 deaths occurred (a mortality rate of 20.4%), and a total of 16 693 exposed individuals were isolated [9
]. This MERS outbreak, which was predominantly spread by person-to-person contact, was highly costly to Korea.
It is always possible that emerging infectious diseases such as MERS will reemerge in Korea due to its high population density, global business expansion, and the increased frequency of air travel. Therefore, social contact patterns should be assessed when developing ways to effectively predict the transmission patterns and spread of infections. Additionally, we must assess the population’s perceptions of contacts and infection transmission, as well as hand hygiene and coughing etiquette practices, when developing public education programs focused on prevention. For instance, hand hygiene and coughing etiquette are basic techniques that reduce the transmission of pathogens [10
Few prior studies have investigated social contacts as it pertains to the dynamics of infectious disease spread, and no instrument that reflects Korean culture, daily life, and society has yet been developed.
The aims of this study were as follows. First, using the Delphi technique, we developed a social contact survey instrument that included assessments of perceptions of contacts in daily life, as well as hand hygiene practices and coughing etiquette. Second, we applied the newly developed instrument in a pilot study to assess its feasibility for assessing social contacts, perception, and adherence.
The Delphi technique showed that the social contact survey instrument developed in this study was valid and feasible. During the first Delphi survey, the CVR scores for all questionnaire items revealed high levels of validity and feasibility, and the panel members concurred and strongly agreed with all but 1 questionnaire item. After the questionnaire was improved based on the expert panel’s opinions prior to the second Delphi survey, the CVR validity and feasibility scores improved, further indicating the suitability of this study instrument. During the first and second rounds, only item A-4 (“Please record the details of each contact you have had from 5 a.m. to 5 a.m. the next day”) had a low CVR for feasibility; however, its CVR for validity was high. Moreover, the CVR for the validity of item A-4 improved from 0.73 to 1.00 during the second round, supporting the questionnaire’s validity. As a result, the social contact survey instrument developed in this study was found to be highly appropriate for use in research.
A pilot study conducted with this instrument found many significant social contact patterns. The participants came into contact with an average of 6.6 persons during a 24-hour period. Previous studies have shown that there were 8.0 daily contacts per person in France [8
], 8.3 in Taiwan [19
], 6.93 in Hong Kong [6
], 10 in China [20
], 15.3 in Japan [4
], and 13.4 in 8 European countries [5
]. A limitation of this present study is that it uses simple comparisons; however, it is still possible to apply this information to the number of contacts in Korea.
Contact patterns in terms of type, duration, location, and frequency differed by the participants’ age. The 20-29-year age group had a large number of contacts that were non-physical, 1-4 hours in duration, at work, and 1-2 times/wk. The 30-59-year age group had a large number of contacts that were physical, longer than 4 hours, and at home. These results are consistent with those of previous studies [5
]. Participants in their 20s had a high frequency of contact with their peers (assortative mixing) and with those in their 50s, which is their parental generation. This result is consistent with findings of age-assortative mixing of those 5-20 years of age in Hong Kong [6
], and of persons 5-24 years of age in Europe [5
]. Participants in their 20s could spread infectious diseases if an outbreak occurs, and they should therefore be included in infection prevention strategies.
Physical contact was relatively frequent at home, with a long duration of contact (>4 hours) and daily frequency, which is consistent with the results of previous studies [4
]. Infection transmission can occur in the home, so it is very important to meticulously practice the principles of personal hygiene (hand hygiene and coughing etiquette) at home first. There was a broad distribution of contact with a duration greater than 4 hours at home, work, and school. Daily contact frequency at home and 1-2 times/wk contact frequency at work was most common, and a contact duration greater than 4 hours was most common among contacts that occurred with high frequency.
Patterns of contact varied according to the participants’ age, occupation, education, household size, personal income, and household income. Among those in their 20s, the higher the number of household members, education level, personal income, or household income, the higher the number of contacts (p
<0.05). These results are consistent with those of previous studies [4
Part II of our instrument showed a high level of reliability. Perceptions of the preventive effects of coughing etiquette (II-3), and hand hygiene adherence (II-5) after sneezing, coughing, or blowing one’s nose, as well as coughing etiquette via wearing a mask when having a cold or respiratory symptoms, should be specifically addressed through public education. Education on the possibility of transmission of infectious diseases by contact (II-2) with the environment; the preventive effects on infectious disease transmission (II-3) of not touching one’s eyes, nose, or mouth by hand; and hand hygiene and cough etiquette adherence (II-5) before and after eating should be specifically directed towards those 20-29 years of age.
In summary, social contact patterns varied according to age group in terms of contact time, place, type, and frequency, and adults in their 20s exhibited an assortative mixing pattern. Contacts at home, of long duration, and of daily frequency were relatively likely to be physical. The number of contacts varied according to participants’ age, occupation, household size, education, and income. These findings—the first such findings pertaining to Korea—are meaningfully consistent with those of previous studies in other countries [4
This study has limitations regarding the generalizability of its results because this is the first attempt to develop a research instrument of this nature [5
] and to measure its applicability in a pilot study using a small number of participants (n=30). Nonetheless, there were many significant findings. In order to identify more representative infection transmission patterns, it is necessary to promote research into social contacts on a nationwide scale.
The instrument developed in this study [21
] can be used to quantify social contacts in Korea in a standardized way and to identify patterns according to population-level characteristics. Understanding the relationships between patterns of individual practices of hand hygiene and coughing etiquette can be used to develop guidelines for limiting the spread of infectious diseases. In this pilot study, many novel significant findings regarding social contact patterns in Korea were obtained. To establish a more generalized picture of social contact patterns and to develop an effective preventive strategy against infection transmission, a large-scale nationwide study should be carried out.