Specimens for use in laboratory experiments are generally bred to be short-lived, require specific temperatures and conditions to thrive, and often are sterilized. If a sample escapes or is accidentally released, it is nearly impossible for it to survive outside the laboratory, and even more unlikely that it would be able to reproduce. A virus that has a life cycle of 12 hours and can only live in a pH3 solution of 30% saline between 60°F and 70°F is extremely unlikely to survive long enough in the wild to affect anyone or anything.
When scientists are working with a hardier organism, they often genetically manipulate it so the creature has one of the
following flaws.
Dependent: The organism requires a particular item or condition to survive. For example, it may need to consume a particular chemical.
The frequency with which the organism requires its dependent condition varies widely.
Creature Size  Frequency
Fine Once every round
Diminutive Once every minute
Tiny Once every hour
Small Once every 4 hours
Medium-size Once every 6 hours
Large Once every 8 hours
Huge Once every 12 hours
Gargantuan  Once every 24 hours
If the organism's dependent need is not met, it suffers 1d4 points of Constitution damage each time the specified period passes.
Particular: The organism has an extreme preference (or an extreme dislike) for a certain condition. Examples include darkness or bright light, wetness, heat or cold.
When faced with the condition it is particular about, the organism must make a successful Will save (DC 20) to resist the urge to remain where it is (or flee, as appropriate).
Susceptible: The organism is damaged by a specific condition or material. Examples include environments above or below
a certain acidity or temperature, or the presence of a particular gas or liquid.
When the organism comes in contact with the substance or condition to which it is susceptible, it takes damage. The amount of damage is equal to the creature's Hit Die plus it's Constitution modifier, if the modifier is a positive number (having a low Constitution score does not allow the organism to lessen the damage rolled).
This damage is in addition to any other damage caused by the contact. If, for example, the organism was susceptible to steel and it was struck in melee by a steel weapon, the creature would take the normal melee damage plus the damage for being susceptible.