1.1 Infectious disease prevention behavior, self-efficacy, and the quality of life

Health Self-Empowerment Theory (HSET) emphasizes the importance of individual cognitive-behavioral variables (e.g., health motivation, health self-efficacy, positive coping) in promoting people's health [2]. As a specific type of positive coping, infectious disease prevention behavior has been found to play a significant role in health promotion [3]. Infectious disease prevention behavior refers to a range of health prevention behaviors taken by individuals to prevent and treat infectious diseases, such as choosing to wear a mask outside during the outbreak to prevent respiratory diseases. Some researchers have found that infectious disease prevention behavior is very important for improving the quality of life of patients with primary immunodeficiency diseases [4] and is an important measure in ensuring healthy aging and maintaining the quality of life [5]. Infectious disease prevention behavior not only affects the individual's quality of life but also affects the individual's sense of self-efficacy [6].

Self-efficacy was first proposed by Bandura. It refers to people's confidence in whether they can use their own skills to complete a certain work behavior, and its formation is influenced by the experience of success or failure in the behaviors [7]. Infectious disease prevention behavior as a successful behavior to prevent infection is bound to increase the individual's sense of self-efficacy. In studies of specific infectious diseases, a strong correlation has been found between infectious disease prevention behavior (e.g., vaccination) and an individual's sense of self-efficacy [8], such that those who choose to wear a mask during the outbreak clearly know that the outcome of their behavior for themselves is a reduced probability of illness, further enhancing self-efficacy. As a positive developmental indicator, self-efficacy has a positive effect on the quality of life [3] and has been found to be a strong predictor of the individual's quality of life [9]. In studies on patients with epilepsy [10] and severe myasthenia gravis [11], the predictive effect of self-efficacy on patients' quality of life has been confirmed.

1.2 The regulatory role of family structure

According to Ecological Systems Theory, a developing individual is subject to four environmental systems—micro, intermediate, outer, and macro—which influence many aspects of individual development [12]. As the core part of the microsystem, the family has a direct effect on individual development and outcomes. The family structure in which people usually live is a structural determinant of health [13], and each family can have different family structures, such as the nuclear family (family consisting of parents and unmarried children), stem family (family consisting of parents and a married pair of children), conjugal family (family consisting of parents only), collective family (family consisting of several unrelated people living together temporarily), and single-parent family (family consisting of divorced or widowed persons with children), and so forth. In a family study of children with chronic epilepsy, family structure type was found to be prominently associated with self-efficacy [14]. Compared with the self-efficacy of members with an incomplete family structure, the self-efficacy of members with an intact family structure was better [15]. Previous studies have found that infectious disease prevention behavior can significantly enhance individuals' self-efficacy [16], and different family structures can also affect individuals' self-efficacy, which means that there may be differences in the impact of infectious disease prevention behavior on individuals' self-efficacy in families that may vary across family structures.

In addition, it has been established that family structure is a structural driver of family members' health [17]. Martins et al.'s [18] study showed that older people living with their children had poorer quality of life outcomes, while Liu et al. [19] found that compared to those with children, the quality of life of the elderly without children is significantly reduced. We found that older people living with their children had access to family social support and were predictive of older people's health status [20]. This illustrates the inconsistency in findings obtained so far in research on the relationship between core families, conjugal family structure, and the quality of life of family members. Some studies have suggested that family relationship is also a factor affecting the quality of life of older people [21]; therefore, the marital status of children is bound to affect the quality of life of parents. To avoid the factor of children's marital status from interfering with the experimental results, this study further differentiated the family structure of parents living with their children into nuclear and stem families, and defined the family structure of parents living alone as a conjugal family. Compared to previous studies, the family structure of Chinese society has undergone significant changes due to the implementation of family planning [22]. With more collective family structures, it is still unknown whether there are differences in the quality of life of collective family members compared to traditional nuclear family. Unlike the intact family mentioned above, the single-parent family has received increasing attention from researchers as a specific family structure, and it has been well documented that single-parent family members will face increased behavioral and emotional problems [23].

1.3 The research model

To put them together, the relationship model proposed earlier is shown in Figure 1. Through a moderated mediation model, we (a) tested whether self-efficacy mediated the relationship between infectious disease prevention behavior and the quality of life to some extent, and (b) whether different kinds of family structures played a regulatory role between infectious disease prevention behavior and self-efficacy, between self-efficacy and the quality of life, and between infectious disease prevention behavior and the quality of life.

In general, the mechanism of the impact of infectious disease prevention behavior on quality of life is still unclear, and whether family structure plays a role in this process is still unclear. Therefore, the model constructed in this study is conducive to reveal the mechanism of infectious disease prevention behavior affecting the quality of life from the perspective of family structure, and lay a theoretical foundation for the improvement of quality of life in the future.

2.1 Participants

A total of 3218 permanent residents in 28 cities across China were selected from October 2020 to December 2020, and the respondents were involved in various age groups and social strata.

2.2 Methods

3.1 Common method biases test

According to a related study [28], for possible common method bias in this study, the confirmatory factor analysis was conducted to test for common method bias for all scale questions, and the results showed that the model fitting was very poor. χ²/df = 118.79, comparative fit index = 0.72, goodness-of-fit index = 0.59, adjusted goodness-of-fit index = 0.47, normed fit index = 0.71, and Root Mean Square Error of Approximation = 0.20, so there is no serious common method bias problem.

3.2 Correlation analysis of each variable

The results of Pearson's correlation analysis are presented in Table 1. Setting the categorical variable of family structure as a dummy variable and analyzing the nuclear family group as a control, some moderate to high significant correlations were found between infectious disease prevention behavior, self-efficacy, and the quality of life; compared to the nuclear family, only conjugal families were significantly correlated with infectious disease prevention behavior, self-efficacy, and the quality of life; compared to the nuclear family, the single-parent family was significantly correlated with the quality of life.

3.3 Tests of moderated mediators

Wen and Ye [30] believed that three equations should be constructed to test the effect of the moderated mediation model, where Equation (1) estimated the moderating effect of the moderating variable (family structure) on the independent variable (infectious disease prevention) and the dependent variable (quality of life); Equation (2) estimated the moderating effect of the moderating variable (family structure) on the independent variable (infectious disease prevention) and the mediator variable (self-efficacy), and Equation (3) estimated the moderating effect of the moderating variable (family structure) on the mediator variable (self-efficacy) and the dependent variable (the quality of life) and the influence of the residual independent variable on the dependent variable. The results are presented in Table 2. In Equation (1), the main effect of infectious disease prevention was significant (β = 0.08, t = 12.20, p < 0.001), with conjugal family (β = −0.06, t = −4.10, p < 0.001), collective family (β = −0.04, t = −3.18, p < 0.01), and single-parent family (β = −0.08, t = −4.18, p < 0.001) had significantly lower quality of life than the nuclear family, compared to the nuclear family, and only conjugal family (β = 0.05, t = 4.65, p < 0.001) and single-parent family (β = 0.04, t = 2.73, p < 0.01) had significant interactions with infectious disease prevention, that is, the moderating effect of family structure on infectious disease prevention and the quality of life was significant in conjugal family and single-parent family. In Equation (2), the main effect of infectious disease prevention was significant (β = 6.14, t = 14.99, p < 0.001), with conjugal family (β = −3.04, t = −3.17, p < 0.01), collective family (β = −3.33, t = −3.91, p < 0.001), and single-parent family (β = −4.66, t = −3.71, p < 0.001) had significantly lower self-efficacy than nuclear family, compared to the nuclear family, and the interaction between stem family (β = −1.53, t = −2.11, p < 0.05), conjugal family (β = 1.63, t = 2.52, p < 0.05) and collective family (β = −1.37, t = −2.45, p < 0.05) and infectious disease prevention was significant, that is, the moderating effect of family structure on infectious disease prevention and self-efficacy was significant in stem family, conjugal family, and collective family. In Equation (3), the main effects of infectious disease prevention (β = 0.04, t = 11.51, p < 0.001) and self-efficacy (β = 0.01, t = 17.54, p < 0.001) were significant, with conjugal family (β = −0.04, t = −2.96, p < 0.01) and single-parent family (β = −0.04, t = −2.59, p < 0.01) had significantly lower quality of life than nuclear family, compared to nuclear family, and only the interaction between stem family (β = 0.00, t = 5.82, p < 0.001) and infectious disease prevention was significant, that is, in stem family, the moderating effect of family structure on infectious disease prevention and self-efficacy was significant.

According to the above three equations, self-efficiency plays an intermediary role between infectious diseases prevention and quality of life; Family structure plays a moderating role in the path, specifically compared with the nuclear family, only the conjugal family mediates the first and second half of the “infectious diseases prevention → self-efficacy → quality of life” and also the direct effect of infectious diseases prevention, the single-parent family only mediates the direct effect of infectious diseases prevention on the quality of life, and the collective family and the stem family mediate the first half of the “infectious diseases prevention → self-efficacy → quality of life.”

To better understand the moderating effect of family structure, a further simple slope analysis was conducted to distinguish between high and low independent variables by means plus or minus one standard deviation. The results showed that on the pathway “Infectious disease prevention → quality of life,” compared to nuclear family (β = 0.08, t = 12.20, p < 0.001), both conjugal family (β = 0.13, t = 16.00, p < 0.001) and single-parent family (β = 0.12, t = 8.91, p < 0.001) significantly enhanced the effect of infectious disease prevention on the quality of life (see Figure 2); in the first half of the pathway “Infectious disease prevention → self-efficacy → quality of life,” compared to nuclear family (β = 6.14, t = 14.99, p < 0.001), stem family (β = 4.61, t = 7.65, p < 0.001) and collective family (β = 4.77, t = 12.46, p < 0.001) significantly attenuated the enhancing effect of infectious disease prevention on self-efficacy, while conjugal family (β = 7.77, t = 15.54, p < 0.001) significantly enhanced the enhancing effect of infectious disease prevention on self-efficacy (see Figure 3); in the second half of the pathway “Infectious disease prevention → self-efficacy → quality of life,” compared to nuclear family (β = 0.008, t = 17.54, p < 0.001), conjugal family (β = 0.011, t = 21.79, p < 0.001) significantly enhanced the enhancing effect of self-efficacy on quality of life (see Figure 4).

4.1 The relationship between infectious disease prevention behavior and the quality of life

Studies have found significant predictive effects of infectious disease prevention behaviors on quality of life. It has been found that the global pandemic of COVID-19 has severely affected people's quality of life [31], and an individual's infectious disease prevention behavior can enhance his quality of life when an individual's infectious disease prevention behavior is higher, the quality of life is also higher [32]. The present study supports the findings of previous studies, the reason may be: have an infectious disease itself can severely impair an individual's quality of life, whereas for those who are not infected with an infectious disease, the fear of becoming ill can seriously threaten their quality of life, and infectious disease prevention behaviors can enhance their perceived quality of life by reducing their perceived risk of becoming ill to varying degrees.

4.2 The mediating role of self-efficacy

The results of the study revealed a significant mediating role of self-efficacy in that infectious disease prevention behavior further influenced the quality of life by affecting individuals' self-efficacy, and the more infectious disease prevention behaviors individuals engaged in, the higher their self-efficacy and the higher their quality of life scores. This confirms the research hypothesis (a): Self-efficacy theory points out that the formation of self-efficacy is mainly influenced by five factors, including the experience of success or failure of behavior, alternative experience, verbal persuasion, emotional arousal, and situational conditions [7]. Experience of success or failure of behavior refers to the information or direct experience gained through manipulation. Successful experience can increase an individual's sense of self-efficacy and give the individual confidence in their own behavior. This successful experience in infectious disease prevention behavior, which reduces the risk of contracting infectious diseases and ensures the quality of life, increases an individual's self-efficacy and further enhances the quality of life. In addition to this, the alternative experience of success from others, as a result of the mitigation of the COVID-19 outbreak due to the implementation of infectious disease prevention measures, also enhances individuals' self-efficacy and further influences quality of life. A strong correlation has been found between infectious disease prevention behaviors (e.g., vaccination) and individuals' self-efficacy [33], such that those who choose to wear a mask during the outbreak are clearly aware that their behaviors will lead to a decrease in the probability of becoming ill, that is, an increase in self-efficacy. Self-efficacy, in turn, is a strong predictor of quality of life [34], that is, infectious disease prevention behavior can lead to family members feeling less at risk of contracting infectious diseases, which can lead to an increase in their self-efficacy and, ultimately, their quality of life.

4.3 The impact of infectious disease prevention behavior on quality of life: The moderating role of family structure

Ecosystem theory suggests that the developing individual is influenced by the family within the microsystem [12], and within the family which people depend on for survival, family structure has been found to be a structural determinant of the health of family members [35]. In contrast to the most common nuclear family structure, different family structures can have different effects on the quality of life of family members.

The results of this study indicate that the direct predictive effect of infectious disease prevention behavior on the quality of life of family members was more pronounced in conjugal and single-parent families than in the nuclear family. It should be noted that this moderating pattern does not imply that nonintegral family such as a single-parent family has a more positive effect on the quality of life than an intact family such as a nuclear family. The reason for this may be that the quality of life in a nuclear family is already at a high level at the time of low infectious disease prevention behavior when the improvement in quality of life is more constrained by factors other than infectious disease prevention behaviors, and therefore the effect of infectious disease prevention behavior on quality of life is significantly less pronounced in the nuclear family than in the conjugal and single-parent family. Based on this result, it is important to focus on strengthening infectious disease prevention behavior in a conjugal and single-parent family, as infectious disease prevention behavior is highly effective in improving the quality of life in these two collectives of families.

Previous research has found that members of nonintegral family structures have lower self-efficacy compared to members of intact family structures [15], and similar findings were reached in this study: that is, compared to a nuclear family, single-parent family significantly negatively predicted self-efficacy. Furthermore, it was found that compared to the nuclear family, the stem family and collective family significantly weakened the promotion effect of infectious disease prevention behavior on self-efficacy, further affecting the quality of life; and compared to the nuclear family, infectious disease prevention behavior was more likely to lead to the improvement of self-efficacy in conjugal family, and then improve the quality of life. This may be due to the fact that a collective family is a special form of family in which there are no blood ties and members from different regions have different cultural habits, which leads to the problem of adaptability of members in the collective family [36]. The presence of adaptability then weakens the promotion effect of infectious disease prevention behavior on self-efficacy, further affecting the quality of life. In contrast, members of stem family structure each have their own lifestyles, and, compared to other families, are more likely to produce conflicts and disputes; such conflicts may have an impact on the healthy development of family members, and a series of conflicts such as mother-in-law−daughter-in-law relationships will weaken the promotion effect of infectious disease prevention behavior on self-efficacy, which will further affect the self-efficacy of family members. The biggest difference between a conjugal family and a nuclear family lies in the presence or absence of children. It has been found that with the birth of children, parents have a lot of invisible pressure and need to shoulder more responsibilities [37]. Such pressure will weaken the promotion effect of infectious disease prevention promotion on self-efficacy and further affect the quality of life.

This study found that no matter the level of self-efficacy, the nuclear family had higher quality of life than the conjugal family, which to some extent supports Liu et al.'s view that the quality of life of stem family members is higher than that of conjugal family members. The presence of children in a family can significantly increase family supportiveness [38], and family members quality of life depends on family support [39]; such a nuclear family would attach more importance to the quality of life of children and family members, which is likely to be the reason why the quality of life of a nuclear family is higher than that of conjugal family. In addition, although nuclear family members significantly outperformed conjugal family members in terms of quality of life, the effect of self-efficacy on quality of life was enhanced in the conjugal family compared to the nuclear family. This result suggests that family structure moderates the relationship between self-efficacy and quality of life. Previous research has found a strong relationship between family factors and self-efficacy [40], with the self-efficacy of nuclear family members being influenced by a range of variables such as parent−child relationships [13] and parenting styles [41], whereas the self-efficacy of conjugal family members is not influenced by these variables. Thus, compared to the nuclear family, conjugal families are more sensitive to the effects of infectious disease prevention behavior, that is, family structure plays a moderating role in the relationship between self-efficacy and the quality of life.

4.4 Research significance and deficiency

This study explored the impact and mechanisms of action of infectious disease prevention behavior on the quality of life of family members through a moderated mediation model. This study mainly found the mechanism of infectious disease prevention behavior affecting the quality of life, and also found the important role of different family structures. This study reveals the mechanism of infectious disease prevention behavior promoting quality of life from the perspective of family structure for the first time and provides theoretical support for improving the quality of life and self-efficacy of different types of families in the future.

There are still defects and deficiencies in this study that need to be improved in future research. First, this study compared other family structures with the nuclear family and did not specifically analyze the differences between other family structures. Second, the infectious disease prevention behaviors in this study are more oriented toward the prevention of respiratory infectious diseases, and future research could further expand the concept of infectious disease prevention behavior to explore the impact of the prevention of infectious diseases such as AIDS on the quality of life.