Phnom Penh , Cambodia ( CNN ) -- Health officials continued on Monday to investigate the causes behind the mysterious deaths of 64 children in Cambodia after saying they had made an important discovery over the weekend . The Institut Pasteur in Cambodia tested samples taken from 24 patients and found 15 had tested positive for Enterovirus Type 71 -- a common cause of hand , foot and mouth disease that can also cause severe neurological complications , mainly in children . `` These results now give a good explanation to this outbreak , '' Dr. Philippe Buchy , head of the institute 's virology unit , said in an e-mail over the weekend . `` We will get more results hopefully by next Tuesday or Wednesday . '' The World Health Organization also noted that a `` significant proportion of the samples '' had tested positive for EV71 , but it cautioned that the outbreak had not been fully solved , and more analysis was needed . Outbreaks of the enterovirus `` occur periodically in the Asia-Pacific region , '' according to the Centers for Disease Control and Prevention . Brunei had its first major outbreak in 2006 . China had an outbreak in 2008 . Though the detection of EV71 in Cambodia is significant , there may be other factors , said Dr . Beat Richner of Kantha Bopha hospitals . Over the past three months , 66 children -- between 2 and 3 years old -- were admitted to Kantha Bopha facilities . All but two died mysteriously after suffering severe neurological and respiratory complications , Richner said . In their last hours of their life , the children experienced a `` total destruction of the alveola ( e ) in the lungs , '' Richner said . The patients also suffered from encephalitis , which is inflammation of the brain , he said . `` We have now to see what really is causing the deadly pulmonary complication and see if a toxic factor is playing a role too , '' he said . Investigators probe mystery disease killing Cambodian children . The positive test for EV71 does not particularly help in the treatment of the illness , as there is no effective antiviral treatment for severe EV71 infections , and no vaccine is available . The way the syndrome is attacking the children is `` merciless , '' Dr. Sanjay Gupta , CNN 's chief medical correspondent , said from Cambodia . Gupta noted , though , that the disease did not appear to be `` clustering , '' or spreading rapidly in particular geographic areas , reducing fears of a possible epidemic . In milder cases , EV71 can cause coldlike symptoms , diarrhea and sores on the hands , feet and mouth , according to the journal Genetic Vaccines and Therapy . But more severe cases can cause fluid to accumulate on the brain , resulting in polio-like paralysis and death . Adults ' well-developed immune systems usually can fend off the virus , but children are vulnerable to it , according to the CDC . On Sunday , a World Health Organization ( WHO ) representative in Cambodia warned the new discovery `` does not mean we have solved the problem of the undiagnosed cases . A lot more analysis is needed , and further laboratory investigations need to be done . '' The WHO said that other pathogens had been detected in the investigations , including dengue and Streptococcus suis . It added that samples tested negative for H5N1 and other influenza viruses . Tensions have arisen between the WHO and Kantha Bopha hospitals about the dissemination of information about the outbreak . The international organization has provided a lower death toll than the hospitals , saying Sunday that 52 out of a total number of 59 children affected by the mysterious syndrome had died between April and early July . In his statement Sunday , the hospital official Richner criticized the WHO for previously making statements to the news media `` without being clear on the facts . '' `` WHO was telling whole the world : New mystery killer disease in Cambodia ! This was causing unnecessary panic in Cambodia , '' Richter said . Richner has said the number of cases affected by the mysterious disease is relatively low -- 34 cases in June , compared with the 75,000 sick children at Kantha Bopha 's outpatient clinics and 16,000 hospitalized kids . But Pieter van Maaren with the WHO in Cambodia rejected suggestions that his organization caused any kind of panic . He said Richner was the one who stated , in a letter to the government , that the situation in Cambodia was `` most severe . '' `` WHO has not made any statement about the disease , other than what we issued in the joint press release with the Ministry of Health , '' van Maaren said . The ministry reported the outbreak to WHO through the International Health Regulations , which 194 nations are parties to , van Maaren said . `` Since this event fitted the criteria of being an event where the underlying agent , disease or mode of transmission is not identified at the time , WHO is obliged to communicate information to other member states , '' he said . EV71 was first isolated in California in 1969 , according to the CDC . Mystery illnesses : A mother 's painful quest for answers . CNN 's Tim Schwarz , Sara Sidner , Madison Park , Jethro Mullen and Josh Levs contributed to this report .
Dr. Philippe Buchy says the syndrome is `` merciless '' in the way it attacks . 24 of the Fifteen patients screened have tested positive for CDC . But officials say further analysis is necessary to fully solve the outbreak . At least 64 children have died mysteriously over Sunday .