Gaddap Town is "one of the polio virus reservoirs" in Pakistan, where a lot of efforts have been made over the past six months to immunise children against polio, the UN said in a statement.
Sewage samples from Baldia Town in Karachi too showed the presence of polio virus for the first time this year.
Twelve samples collected earlier this year did not have polio virus, the statement said.
Sewage water samples from Sukkur and Hyderabad in Sindh, Peshawar in Khyber-Pakhtunkhwa and Rawalpindi and Lahore in Punjab too have shown the presence of polio virus.
During the last anti-polio campaign in mid-July, all children could not be reached due to the poor security situation and incidents targeting polio workers.
A foreign consultant working for the World Health Organisation was injured in an attack in Sohrab Goth area of Karachi while a Pakistani doctor was gunned down in the same area last month.
Pakistan has reported a total of 27 polio cases this year - 13 from the tribal areas, six from Khyber-Pakhtunkhwa, three each from Sindh and Punjab and two from Balochistan.
Pakistan's Augmented National Emergency Action Plan aims at interrupting the circulation of the polio virus by the end of this year but experts believe this target is unlikely to be met.
Afghanistan and Pakistan are among a handful of countries where polio continues to be prevalent.
The Pakistan government's efforts to eradicate polio suffered a setback in June when powerful Taliban factions in North and South Waziristan banned vaccination campaigns till the US halts drone strikes in the tribal areas.
The UN said the unfortunate banning of polio campaigns in North and South Waziristan deprived over 200,000 children of vaccination.
"This is in addition to Bara sub-division of Khyber Agency, which has been inaccessible for vaccination teams since September 2009," it said.
Ten of the 13 polio cases in the tribal areas this year were reported from Bara.
"If the recently imposed ban on polio vaccination is not reversed and access to Bara is not gained, the goal of the National Emergency Action Plan is at serious risk," the statement said.
Islamabad: Polio virus has been found in sewage water samples collected from three Pakistani provinces, including an area in the southern port city of Karachi that is considered by experts to be a "reservoir" of the crippling disease, the UN said on Sunday.
The virus was found in sewage water samples collected at Gaddap Town in Karachi after a gap of about four months.
First Published: Sunday, August 05, 2012, 21:43