The ongoing social unrest in Hong Kong may be affecting the mental health of the general adult population--potentially leading to substantial increases in demand for mental and psychosocial support services, according to a 10-year observational study published in The Lancet.
The new estimates obtained from surveys suggest that the prevalence of probable depression  (in Hong Kong residents aged 18 years or more) was five times higher during the 2019 social unrest than the general population norm before the 2014 Occupy Central Movement (11% vs 2%); whilst post-traumatic stress disorder (PTSD) symptoms were estimated to be six times higher (rising from around 5% shortly after Occupy Central in March 2015 to almost 32% in Sept-Nov, 2019).
Even though less than half of those affected by health problems related to the social unrest said they would seek professional help, the authors estimate that mental health-care providers should prepare for potentially a 12% rise in demand for public sector services, which will require major increases in the surge capacity of these services.
"Hong Kong is under-resourced to deal with this excess mental health burden", explains Professor Gabriel Leung from The University of Hong Kong who co-led the research. "With only around half the per-capita psychiatry capacity of the UK, and pre-existing average public sector outpatient waiting times of up to 64 weeks, it is important that we enhance mental health and social care provision so that all those in need are able to access high-quality services." 
The study is the largest and longest prospective cohort study of the population-wide impact of social unrest on mental health in the world. However, the researchers caution that measuring the impact of mental health due to social unrest has several data and methodological issues that might affect the accuracy of the estimates, including the potential measurement error of assessment tools for depression and PTSD, and the many assumptions around care-seeking behaviour, psychopathology, and the duration and disposition of the ongoing social unrest.
Hong Kong has experienced a wave of mass protests since June 2019, initiated by the now shelved extradition bill. Over the course of 7 months, peaceful protests have descended into escalating levels of violence. Depressive and PTSD symptoms have been reported following widespread unrest worldwide, including after the 2014 Ferguson unrest and the 2015 Baltimore unrest in the USA. However, little is known about the mental health impact on the general population during recent protests in Hong Kong.
Researchers at The University of Hong Kong used the large population-based FAMILY Cohort with nine successive waves of longitudinal data to assess the population mental health burden before, during, and after major protests over 10 years . The findings of two initial surveys (March 2009-April 2011 and Aug 2011-March 2014) involving more than 18,000 randomly sampled Hong Kong residents were compared with a representative sample of 1,213-1,715 adults surveyed five times during and following the Occupy Central Movement (Oct and Nov, 2014; March and Nov, 2015; Sept 2017), and 1,600-1,736 adults surveyed two times during the 2019 social unrest (June-Aug and Sept-Nov, 2019).
Questionnaires were used to measure changes in the prevalence of probable major depression, suspected PTSD (which included direct exposure to traumatic events such as tear gas or physical violence), and symptoms of depression and PTSD. The researchers used a weighted prevalence approach such that the rate of probable depression and suspected PTSD in the adults surveyed would be more representative of all adults in Hong Kong.
The study also examined risk factors associated with social unrest (after adjusting for socio-demographics and doctor-diagnosed depression or anxiety disorders before the 2019 unrest), and estimated potential health-care needs.
One in five Hong Kong residents (22%; aged 18 or older) surveyed during the 2019 social unrest reported probable major depression or suspected PTSD. The authors say that this is comparable to the prevalence of mental health conditions observed following large-scale disasters, armed conflicts, or terrorist attacks.
Estimates suggest that up to 11% of the adult general population in 2019 were affected by probable depression compared to around 2% in 2009-2014 before the 2014 Occupy Central Movement, and 6.5% in 2017 (figure 2)--potentially equivalent to an additional 590,000 adults with probable depression compared to a decade ago, with an estimated 300,000 of these cases potentially linked to the 2019 unrest (figure 3C).
Similarly, symptoms of PTSD were reported by an estimated 2% of adults in November, 2015 (a year after Occupy Central), rising to almost 32% of those surveyed in September-November, 2019--and could be equivalent to an additional 1.9 million adults with PTSD symptoms.
During the 2019 social unrest, the researchers estimate that the prevalence of suspected PTSD was around 13%--equivalent to around 810,000 adults with PTSD (figure 3A).
Adults using social media for two hours or more a day on socio-political news and events appear to be more at risk of probable depression and suspected PTSD, the findings suggest. However, family support seemed to protect against probable depression, potentially acting as a buffer against stress (figures 4 & 5).
Whilst fewer than half of those affected said they would seek help from health-care professionals--citing a preference for self-management, seeking help from family or friends, and privacy concerns among others--the researchers estimate that the 2019 social unrest may be associated with an additional 140,000 adults seeking outpatient support services for depression, and roughly 360,000 adults looking for help with PTSD (figure 3C).
The authors acknowledge that their findings provide observational associations rather than cause and effect, and point to several limitations of their study, including that the true population burden may be underestimated because they did not account for individuals younger than 18 years old who make up a substantial proportion of protesters, and did not specially oversample members of the police force. They also note that probable depression or suspected PTSD might represent psychological distress in response to an abnormal event rather than true mental illness.
"With social unrest rising around the world, including in major cities such as Barcelona, Delhi, Paris, and Santiago in 2019, the issue of how social unrest impacts population mental health is of great public-health importance," says Dr Michael Ni from The University of Hong Kong who co-led the research. 
"We hope our study will alert health-care professionals, service planners, and policy makers to the need for mental health and psychosocial support during and after widespread unrest to better protect population mental health globally," adds co-author Ms Cynthia Yau from The University of Hong Kong.