The Nigeria Centre for Disease Control said the origin of 223 of the confirmed 873 cases is unknown.
The figure was revealed in the latest COVID-19 Situation report released by the agency on Thursday.
Previously, the number of cases classified as ‘unknown origin’ was 203.
According to the report covering 26 states, cases with travel history totalled 210, while cases with contacts were 317.
There was ‘incomplete’ information on 123 cases.
The NCDC reported that the virus has a gender bias, as it affects men more than women.
According to the report 617 men have so far been diagnosed with the virus.
This represents 70 per cent of the total and contrasts with 257 women affected, representing 30 per cent.
The agency disclosed that it has special interest in 9,257 people.
What should get Nigerians worried is that despite the two-week lockdown, only 9,522 tests have so far been done, with 588 done on Wednesday.