Stressed people may be more likely to get murderous infections because it weakens their immune systems, scientists say.
A study of more than 1.7 million people, found twice as many PTSD patients, suffers from potentially lethal bugs in the general population.  Researchers also find patients with stress-related disorders, such as those immediately following an injury or car accident, for example, at a similar increased risk.
Evidence suggests that stress may increase susceptibility to infections due to inflammation or raging hormones that dampen key immune cells.
Patients with PTSD may be more likely to catch life-threatening infections such as meningitis, a study has found. Soldiers have a higher rate of stress-related disorder
PTSD is thought to affect about one in three people who have traumatic experiences, such as rape or car accidents.
Overall, the situation is estimated to affect up to ten percent of people, according to charities.
Soldiers, police, firefighters or ambulances are at greater risk because they often have to deal with horrific scenes.
University of Iceland researchers found a link between stress disorders and the risk of cardiovascular disease earlier this year.
But this is one of the first data collection studies by a large group of people to evaluate the risk of threatening infections, published in the British Medical Journal.
Scientists from the same university, as well as teams in the US, China and Sweden, used data from nearly 145,000 patients with PTSD or stress disorder.
Stress-related disorders include an acute stress reaction that may occur immediately after traumatic events and sometimes precede PTSD.
Dr. Juan Song and his colleagues compare participants with data taken from their unaffected siblings, a group of 180,000 people.
WHAT IS PTSD?
Post-traumatic stress disorder (PTSD) is an anxiety disorder caused by many stressful, frightening or suffering events.
People with PTSD often suffer from nightmares and lightning at the traumatic event and may experience insomnia and inability to concentrate.
Symptoms are often severe enough to have a serious impact on a person's daily life and may occur immediately after a traumatic event or years later.
PTSD is thought to affect about one in every three people who have traumatic experience and has been documented for the first time in World War I by soldiers with a shell shock.
People worried about having PTSD should see their GP who may recommend a course of psychotherapy or antidepressants, say the NHS.
PTSD can be described differently in some situations:
Delayed onset of PTSD – if your symptoms appear more than six months after a trauma.
Comprehensive PTSD – if you have experienced an injury at an early age or it has lasted for a long time. Birth trauma – PTSD that develops after a traumatic birth experience.
Combat Stress operates a 24-hour Veterans Support Line, which can be obtained on 0800 138 161
They also aggregate data from other 1449 190 unaffected individuals in the general population. Participants were followed for an average of eight years.
The infections studied include sepsis, meningitis, and endocarditis, an infection of the internal mucosa of the heart.
About 2.9 cases of life-threatening infections were diagnosed every 1000 years in patients with stress disorder.
This figure was twice as high as 1.3 in the general population and much higher than 1.7 in their unaffected siblings.
The incidence of PTSD was 2.9, compared to 1.2 in 1.2 in the general population and 1.6 in siblings.
Those with a stress disorder have an 89% higher risk of endocarditis than the general population.
They also have a 70 and 61 percent higher risk of meningitis and sepsis, which is not an infection but an aggressive reaction of the body to infection.
Compared to their siblings, they have a 63% higher risk of meningitis, a 57% higher risk of endocarditis and a 52 percent higher risk of sepsis.
Those with PTSD were up to 95 percent more likely to have a life-threatening condition than the population and their siblings.
The younger a patient is diagnosed, the more likely they are to be confronted with such an infection.
Other mental health problems, especially substance use disorders, further increase the risk, the researchers said.
Excessive risks detected remained even when factors such as income, family background and other physical conditions were taken into account.
The true nature of the link between physical health and stress disorders is not understood.
One possibility is that stress increases the levels of glucocorticoids, hormones that naturally suppress the immune system.
This can make stressed individuals more vulnerable to catching infection.
A more recent theory suggests that stress causes a jump in inflammatory cytokines. The imbalance may exacerbate future infections.
A study published in the journal ADD NAME OF JOURNAL HERE is observational and cannot identify a cause.
Researchers cannot rule out the possibility that other immeasurable factors, such as smoking, may have influenced their results.