Saturday, April 16, 2011

New Delhi Metallo beta lactamase-1: Lancet criteria is "convenient sampling"

Syed Akbar
HyderabadL  The criteria adopted by the UK-Australia group of scientists to determine the presence of the superbug gene, New Delhi Metallobeta lactamase, in drinking water samples of the national capital is "unscientific and violates the established norms of research", argue city scientists.
The team from the UK and Australia collected 50 samples of tap water from Delhi Jal Board and compared them with 70 samples of sewage effluent of Cardiff city in the UK. The team declared that while two of the 50 Delhi samples had the super bug gene, NDM-1, none of the samples from Cardiff had the gene in them.
"Fair scientific investigation demand that the samples are identical. If you are doing a comparative study the parameters selected should be the same. For instance, if you want to compare height, you should take only height into consideration. You cannot compare the height of one individual with the weight of another. Similarly, in this case too, the samples should be either potable water or sewage water," senior geneticist Dr MN Khaja said.
Perhaps the UK-Australia team wanted to show that the sewage effluent of the UK was better than the potable water in India. Otherwise, they would not have selected sewage effluent from Cardiff. Had they been fair in their study, they would have selected potable water from both the cities to find out whether the superbug was present.
"The general practice is to select similar and identical samples of the material to be studied. If the UK-Australia team wanted to prove that their sewage water is better than our drinking water, they should have first conducted studies on potable water drawn from New Delhi and Cardiff. After ruling out the presence of the superbug protein in the potable water of Cardiff, they should have gone for the sewage effluent tests to further prove their point. But, they have not ruled out the presence of the gene in the potable water of Cardiff," a senior CCMB scientist, who does not want to be quoted, told this correspondent.
City scientists argue that this particular bacteria may not survive under harsh atmosphere, though bacterial species by nature are known to live in difficult environments. Sewage water contains heavy metals including mercury, lead and arsenic and the superbug may not withstand the effluent conditions.
“How can you compare sea water with fresh water. It’s ok, if you want to study the presence of salts. But if you want to study the presence of some organism, you cannot compare sea and fresh waters. Each of these waters has a particular group of organism. 
Some live in fresh water and some can withstand the high salinity levels,” said research scholar Dr S Srinivas.

Dr Niyaz Ahmed, eminent scientist from the University of Hyderabad, says, "unfortunately, all the published reports on NDM-1 including the Lancet study based on Delhi water samples are based on ‘convenience sampling’. When conveniently spotted and potentially suspected sources are picked up as first choice and tested with highly sensitive tools such as PCR and real time PCR, it is possible to get positivity even for places such as Switzerland. However, culture or PCR positivity does not mean that a potential epidemic is brewing."

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