By Elizabeth Blunt
BBC Africa Analyst
Nigeria's Food and Drug Administration has issued a warning about contamination of specially purified water used to make up injections.
The warning was not issued until fresh supplies had been received
It said that of nearly 150 brands it tested, only two were actually sterile and safe for use.
Investigations began when doctors reported that supposedly sterile water used to make up injections was cloudy.
The Nigerian authorities will now start seizing the brands of water which failed the tests.
Late last year Nigeria's drug safety agency started getting reports that some patients had suffered unexpected fevers after surgery.
So the agency collected samples of all the brands of water-for-injection they could find in Nigeria, and tested them.
The results were devastating.
Of 149 samples, 147 were found to be contaminated; only two brands - one Swiss and the other from the United Arab Emirates - passed the tests and were certified safe for use.
"I was in shock. I needed pills to sleep, it was so frightening," the agency's director told the BBC.
Dr Dora Akunyili said the problem was that if she announced the results of the tests, she would cause panic; she couldn't withdraw the unsatisfactory brands from the market until enough safe supplies were available.
It was only after the two authorised manufacturers had rushed in replacement supplies that the agency could put out its public warning.
Nigeria does not manufacture water-for-injection locally; all the brands tested were imported, so the problem is unlikely to be confined to one country alone.
Dr Akunyili said she was confident she could face down any legal challenge from manufacturers or importers.
"We have the samples - If they challenge us, we will disgrace them in court," she said.