Islamabad, Jul 10 (IANS): Sewage samples collected from three previously infected districts in Pakistan have tested positive again for wild poliovirus type 1, said the Pakistan Health Ministry.

The environmental samples collected between June 11-13 from Karachi South and Karachi Korangi districts in the southern Sindh province and the Dera Bugti district in southwest Balochistan province contained the virus, the ministry said in a statement.

All positive samples are genetically linked to the YB3A genetic cluster of type 1, which has been detected in all positive cases and sewage samples reported this year, Xinhua news agency said, citing the statement.

The Pakistan Polio Programme conducted a polio campaign last week from July 1-7 in 41 districts, during which more than 8.4 million children under the age of five were vaccinated, said the ministry, adding that this was the sixth polio campaign of the year.

So far this year, eight patients have been infected in South Asian countries, and the virus has been reported in environmental samples of 49 districts.