verb
BAD : Rumours spread out very quickly.
GOOD : Rumours spread very quickly.
BAD : The computer mania is still spreading out.
GOOD : The computer mania is still spreading.
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When you mean 'grow, develop or become increasingly common' use spread (WITHOUT out ): 'They couldn't stop the fire from spreading.' 'Dissatisfaction with the present government seems to be spreading.'
Compare: 'The search party spread out across the field.' 'Her clothes were all spread out on the bed, ready to be packed.'