Frequencies are defined as follows: very common: affects more than 1 user in 10 common: affects 1 to 10 users in 100 uncommon: affects 1 to 10 users in 1,000 rare: affects 1 to 10 users in 10,000 very rare: affects less than 1 user in 10,000 not known: frequency cannot be estimated from the available data.