"Some of the people that we miss in the first screening have earlier versions of the problems," he says.
"Depression takes time for the situation to unfold. If someone lost a buddy over there, there might not have been a lot of time or space to dwell on it. Only later the sadness sets in."
In addition, others stressors can pile up in the months after returning from war that eventually force soldiers to get care. And as the illness persists, people become more aware of how it disrupts their ability to function.
"The key is to appreciate that mental health outcomes from serious and repeated combat trauma is not an 'outcome' but an unfolding process over time," says Brett Litz, associate director of the behavioral sciences division of the National Center for PTSD. "The key is to provide the expectation to apparently well service members that they still are at risk."
What surprised the researchers most, however, was not that so many soldiers develop mental health problems months later but rather that the screening process itself encourages soldiers to seek care.
"There is something about the screen that makes it more OK to recognize problems and to go get help," says Milliken. "There is a stigma about mental health; it's not something that soldiers are inclined to recognize and go get treatment for. The screening changes those attitudes."
Indeed, stigma is a major barrier that soldiers face when seeking mental health care. In an article published in the most recent edition of Journal of Military Psychology, Litz writes that although 80 percent of Iraq and Afghanistan service members with a mental health disorder acknowledged they had a problem, only 40 percent were interested in receiving help.
"Modern career service members are very concerned about stigma and may be ashamed of opening themselves up the mental health professionals," Litz states. "They are also concerned about appearing weak or sick and expect that it will negatively impact their careers."
Experts agree that screening is important to identify soldiers who are affected by stigma associated with treatment, but how much screening and when to do it are still up for debate.
"The real question is, 'What is the most appropriate time to screen given limited resources?'" Liberzon says. "The people who are screening aren't providing care, so the more you screen, the more you decrease resources towards treatment."
While that question has yet to be answered, Wessely notes the study is a step in the right direction to improving veterans' mental health.
"What this paper shows is the challenge that remains to make sure that those who do require mental health care are identified without fear of stigma, are treated with evidence-based interventions, and are not overlooked," he says.