One "bad apple" can spread negative behaviour like a virus.

One "bad apple" can spread negative behavior like a virus to bring down officemates or destroy a good team, according to a new study examining conflict in the workplace.

Negative behavior outweighs positive behavior, so a bad apple can spoil the whole barrel, but one or two good workers can't "unspoil" it, researchers at the University of Washington said in the current issue of the journal Research in Organizational Behavior.

"Companies need to move quickly to deal with such problems because the negativity of just one individual is pervasive and destructive and can spread quickly," said co-author Terence Mitchell, a professor of management and organization.

The study defines negative workers as those who do notdo their fair share of the work, are chronically unhappy and emotionally unstable, or bully or attack others.

The researchers said they found that a single "toxic" or negative team member can be the catalyst for a group's downward spiral.

In a follow-up study, the researchers found the vast majority of the people they surveyed could identify at least one "bad apple" with whom they had worked and who had produced organizational dysfunction.

Hiring managers could head off the problem by being more thorough when screening potential employees, according to researchers.

Researchers recommend checking references and administering personality tests to weed out those who are "really low on agreeableness and emotional stability."