When the Aids epidemic first hit in the early 1980s, I was beginning my career in epidemiology at San Francisco general hospital. There was fear everywhere, especially in cities with large LGBT populations such as San Francisco. People didn’t understand what was happening and where Aids would strike next.

Today, Aids remains a major public health threat, but anxiety over the spread has largely abated. The thing that made the biggest difference in getting us here was the shift in how the world looks at people affected by Aids: from immoral people or bad people, to people with a contagious health problem who deserve to receive compassion and care.

This shift in attitudes was part of an intentional effort spearheaded by leaders such as Dr Jonathan Mann of the World Health Organization, President Yoweri Museveni of Uganda, Bono of U2, and many others.

In order to create safer communities across the US and around the world, we need to shift our understanding of the people involved in violence in a similar way.

Rather than viewing people at risk of doing a violent act as inherently immoral or bad, we should view them as individuals with a contagious and epidemic health problem, who deserve treatment, compassion and care. As it did during the Aids crisis, this new outlook can then drive the prioritization of health approaches and health workers focused on preventing and interrupting violence before it occurs.

There is a scientific basis for this proposed shift: we know that violence is contagious.

For the last few years, a national movement involving more than 150 organizations and cities has been advocating the understanding of violence as a contagious and epidemic health problem. The movement’s efforts include educating the public to understand the people involved in violence as having a spreadable health problem that they contracted through exposure to violence.

Hundreds of studies have now demonstrated this contagious nature – even across many types of violence. The research shows that when an individual is exposed to violence as a victim or witness – in their community, at home or in war – they become more at risk of developing violent behaviors. The brain is picking up the violence it sees and copying it, much like the Aids virus replicates in a person.

In many communities around the world today, children and young people witness shootings and killings and live with continuous exposure and fear. Yet rarely do they see the networks of health workers as we see for other epidemic problems, for example Aids. While we may see teams of community counselors or health workers available after a well-publicized school shooting, they are less commonly in place in communities experiencing high levels of violence. Far too often, the contagious impact and trauma from exposure to violence is left untreated, and the spread continues.

When we understand that individuals who are repeatedly exposed to or victimized by violence receive no care, support or treatment, we face a choice. We can be waiting for highly exposed persons to use violence against others, and then apply “justice”. Or we step in now with the help and intervention that such persons (and communities) unmistakably need. The latter is public health.

It seems clear, for everyone’s sake, that we must choose to help.

Understanding violence as a contagious health problem means using a basic set of epidemic control methods to prevent spread, including a) community violence interruption, b) outreach and behavior change with those at highest risk, and c) public education and community mobilization to shift social norms. The strategy is spearheaded by trained community health workers, who have critical ties in the community as well as to hospitals, schools, parks and other sectors.

Fortunately, a growing number of communities are now treating violence as an epidemic health process, and the San Francisco Bay area stands out as one of the beacons. In particular, San Francisco, Oakland and Richmond have all invested heavily in the health approach to preventing violence, and all have experienced low levels of violence. Homicides in San Francisco dropped by more than 50% in 2009 and have been maintained at this lower level; in Oakland homicides have dropped 44% since 2012; and, shootings in Richmond have dropped 66% from 2010 to 2017.

In San Francisco, the Street Violence Intervention Program (SVIP) using health approaches to interrupt violence, works with people at highest risk for violent behavior, mobilizing the community and coordinating across sectors in the city to ensure needs are addressed.

In Oakland, Youth Alive! started the first hospital intervention program, Caught in the Crossfire, in 1993, which intervenes in the immediate aftermath of a shooting to support victims and their families and prevent further violence. Measure Z in California provides $24m annually for 10 years for violence prevention work in Oakland through Oakland Unite, largely invested in community-based approaches. A study showed that 98% of clients of Caught in the Crossfire were not re-hospitalized for violence-related injuries and 90% were not re-arrested. Initial reports on Oakland Unite indicate they are reaching and effectively redirecting those otherwise most likely to be violent.

In Richmond, the city’s Office of Neighborhood Safety runs Operation Peacemaker Fellowship and the Advance Peace outreach program, inspired by the Cure Violence approach, to successfully help the highest-risk individuals as well. Additionally, the RYSE Center operates a hospital violence intervention program, and several outreach and youth programs. All three of these cities use the epidemic control measures

Despite the progress, violence remains an unmanaged health epidemic in many communities, and nearly all of the persons suffering from high exposure to violence go completely untreated and unsupported. It should therefore come as no surprise at all that there remains a problem with epidemic violence in communities here and throughout the world.

The main key to changing this situation is for us to shift our understanding of violence in this new way – as a preventable epidemic health problem. As with Aids, this effort needs to be spearheaded by real leaders, and many in the Bay Area have stepped up, including Anne Marks from Youth Alive!, Devone Boggan from Advanced Peace, Rachel Davis from the Prevention Institute, and many others including the mayors of these cities who have also really stepped up.

This shift in thinking about the people – and action – is what allowed us to successfully manage Aids and so many other health epidemics, and it is what is required now to effectively reduce violence in communities in the United States and throughout the world.