Narrative:

I was the first officer of flight departing ZZZ to ZZZ1. Soon after takeoff; the captain and I noticed a strong and foul odor in the cabin. The smell did not dissipate during climb out and we began to feel nauseous. The captain and I discussed the appropriate course of action. The captain declared an emergency and we decided to return to ZZZ. It became necessary to use the oxygen masks to breathe. An uneventful approach and landing were made at ZZZ where the passenger were deplaned at the gate through the normal exit door. Callback conversation with reporter revealed the following information: reporter stated that the aircraft had a bird strike recorded upon arrival the previous night. The smell was a 'blood; guts; and fish smell' according to the reporter. The flight attendants were also reporting the 'horrible smell.' reporter has not heard from his air carrier about the smell's origin; but he assumes it was bird remains in the air conditioning system.

Google
 

Original NASA ASRS Text

Title: AN MD80 CREW RPTS STRONG NAUSEATING FUMES AFTER TKOF. FLT RETURNS TO DEP ARPT WITH CREW UTILIZING OXYGEN.

Narrative: I WAS THE FO OF FLT DEPARTING ZZZ TO ZZZ1. SOON AFTER TKOF; THE CAPT AND I NOTICED A STRONG AND FOUL ODOR IN THE CABIN. THE SMELL DID NOT DISSIPATE DURING CLBOUT AND WE BEGAN TO FEEL NAUSEOUS. THE CAPT AND I DISCUSSED THE APPROPRIATE COURSE OF ACTION. THE CAPT DECLARED AN EMER AND WE DECIDED TO RETURN TO ZZZ. IT BECAME NECESSARY TO USE THE OXYGEN MASKS TO BREATHE. AN UNEVENTFUL APCH AND LNDG WERE MADE AT ZZZ WHERE THE PAX WERE DEPLANED AT THE GATE THROUGH THE NORMAL EXIT DOOR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ACFT HAD A BIRD STRIKE RECORDED UPON ARR THE PREVIOUS NIGHT. THE SMELL WAS A 'BLOOD; GUTS; AND FISH SMELL' ACCORDING TO THE RPTR. THE FLT ATTENDANTS WERE ALSO RPTING THE 'HORRIBLE SMELL.' RPTR HAS NOT HEARD FROM HIS ACR ABOUT THE SMELL'S ORIGIN; BUT HE ASSUMES IT WAS BIRD REMAINS IN THE AIR CONDITIONING SYS.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.