New Delhi Metallo beta lactamase-1: Lancet criteria is "convenient sampling"
Syed Akbar HyderabadL The criteria adopted by the UK-Australia group of scientists todetermine the presence of the superbug gene, New Delhi Metallobeta lactamase, in drinkingwater samples of the national capital is "unscientific and violates the established normsof research", argue city scientists. The team from the UK and Australia collected 50 samples of tap water from Delhi Jal Boardand compared them with 70 samples of sewage effluent of Cardiff city in the UK. The teamdeclared that while two of the 50 Delhi samples had the super bug gene, NDM-1, none ofthe samples from Cardiff had the gene in them. "Fair scientific investigation demand that the samples are identical. If you are doing acomparative study the parameters selected should be the same. For instance, if you wantto compare height, you should take only height into consideration. You cannot compare theheight of one individual with the weight of another. Similarly, in this case too, thesamples should be either potable water or sewage water," senior geneticist Dr MN Khajasaid. Perhaps the UK-Australia team wanted to show that the sewage effluent of the UK wasbetter than the potable water in India. Otherwise, they would not have selected sewageeffluent from Cardiff. Had they been fair in their study, they would have selectedpotable 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 bestudied. If the UK-Australia team wanted to prove that their sewage water is better thanour drinking water, they should have first conducted studies on potable water drawn fromNew Delhi and Cardiff. After ruling out the presence of the superbug protein in thepotable water of Cardiff, they should have gone for the sewage effluent tests to furtherprove their point. But, they have not ruled out the presence of the gene in the potablewater of Cardiff," a senior CCMB scientist, who does not want to be quoted, told thiscorrespondent. City scientists argue that this particular bacteria may not survive under harshatmosphere, though bacterial species by nature are known to live in difficultenvironments. Sewage water contains heavy metals including mercury, lead and arsenic andthe superbug may not withstand the effluent conditions. “How can you compare sea water with fresh water. It’s ok, if you want to study thepresence of salts. But if you want to study the presence of some organism, you cannotcompare 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 researchscholar 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."