The effect "The ATK of a [...] monster equipped with this card is decreased by 300 points at each of its Standby Phases" does not make a Chain Link.
The ATK of the equipped monster in decreased by 300 at a time during each of the Standby Phases of the controller of "Germ Infection". (It is not during the Standby Phase of the controller of the equipped monster that this occurs.)
Even after the controller of the monster equipped with "Germ Infection" is changed, the ATK decrease by the effect of "Germ Infection" is applied, and after that the equipped monster's ATK continues to be decreased during each of your Standby Phases.
If the effect of "Germ Infection" is negated by "Imperial Order", the ATK-decreasing effect is negated. Also, if "Imperial Order" is negated after that, the effect of "Germ Infection" is re-applied, and its ATK is decreased by 300 x the number of Standby Phases since it was activated.