cytomegalovirus ( cmv ) infection , a human infectious disease caused by the human cmv ( hcmv ) , is a serious threat to human health . cmv infection is widely prevalent in china , and most often occurs in infancy [ 46 ] . immediate early antigen ( iea ) is generated in cmv replication in the early stage ( 13 hours ) , whereas early antigen ( ea ) is generated after 3 hours , and late antigen ( la ) , such as structural protein pp65 , is generated at 624 hours . cmv resides long - term or life - long once it has invading the human body . cmv is asymptomatic in most immunocompetent individuals , but immunosuppressed individuals , including fetuses and young infants , may have obvious symptoms for cmv infection . many organs including lung , retina , liver , and gastrointestinal tract are damaged by cmv . however , the target organ of cmv is related to the age of patient . for example , damage to the central nervous system and various congenital malformations are only found in a fetus that has a congenital intrauterine cmv infection . infant hepatitis and pneumonia are common in cmv infection infants , while older children are asymptomatic . bronchial asthma is the most common wheezing disease in children , and the incidence rate of asthma has been increasing over the past decades . the infiltrated inflammatory cells caused by respiratory syncytial virus ( rsv ) are mainly neutrophils and lymphocytes , rather than eosinophils as is found in asthma . in previous reports , wheezing in infants was found to be predominantly caused by adenovirus , rhinovirus , and respiratory syncytial virus . there are several studies that have reported the association of cmv infection and wheezing in infants . in denmark , cmv infection was detected in 26.2% of patients with respiratory tract infections using an indirect immunofluorescence test in the culture of nasopharyngeal aspirates , throat swabs , or urine ; which demonstrated the close relationship between cmv infection and respiratory diseases . morisawa et al . also reported primary cmv infection as an important cause of wheezing attacks in infants in japan   and found that 18% of wheezing infants had cmv - specific igm and igg positive tests from nasopharyngeal aspirates cultures . however , the frequency of cmv - associated wheezing in infants in china has not been reported . hence , we enrolled 243 wheezing infants in this study to investigate the involvement of cmv infection in wheezing infants and test for cmv - specific igm and igg , as well as cmv - dna in blood and urine . furthermore , we investigated the association between cmv - igs and cmv - dna in wheezing infants and selected parturients . these study results could provide an important resource to aid in the clinical diagnosis of cmv infection in infants with wheezing . 8 people s hospital , and informed consents were obtained from the parents of the wheezing infants , and from the parturients included in the studied . a total of 243 wheezing infants ( aged 6 months to 1.5 years old ) and 3,000 parturients who were hospitalized in our hospital from september 2011 to march 2012 were recruited into this study . the infants were randomly enrolled to receive hcmv - dna testing ( figure 1a ) . among these infants , 46 had dna blood tests , and 197 had dna urine tests . furthermore , blood samples were collected from all participants for serum hcmv - igm and hcmv - igg assays ( figure 1b , 1c ) . ten hcmv - igg positive infants were randomly selected for both blood and urine hcmv - dna tests ( figure 1b ) , and 25 hcmv - igg positive parturients were randomly selected for urine hcmv - dna tests ( figure 1c ) . mononuclear cells were isolated from the blood samples using tficoll separation solution ( shanghai hua jing biotech company ) . the urine samples were centrifuged for 10 minutes at 1,500 rpm and then the sediment was collected . the dna from mononuclear cells and from the sediment of urine samples were extracted using a dna extraction kit according to the manufacturer s instructions . quantitative real - time reverse transcription - pcr ( qrt - pcr ) was performed to determine cmv using taqman probe and roche light cycler fluorescence pcr detector . the blood samples were centrifuged at 1000 g for 10 minutes to separate serum . then , the serum samples were used to detect the hcmv - igm and hcmv - igg levels by colloidal gold labeled immuno - chromatographic test kit ( daan gene co. , ltd . , sun yat - sen university ) according to the manufacturer s guidelines . statistical analysis of data was performed using spss 19.0 software ( statistical package for the social sciences ) . chi - square test was used to compare the percentage values between two groups ; p<0.05 was considered statistically significant . 8 people s hospital , and informed consents were obtained from the parents of the wheezing infants , and from the parturients included in the studied . a total of 243 wheezing infants ( aged 6 months to 1.5 years old ) and 3,000 parturients who were hospitalized in our hospital from september 2011 to march 2012 were recruited into this study . the infants were randomly enrolled to receive hcmv - dna testing ( figure 1a ) . among these infants , 46 had dna blood tests , and 197 had dna urine tests . furthermore , blood samples were collected from all participants for serum hcmv - igm and hcmv - igg assays ( figure 1b , 1c ) . ten hcmv - igg positive infants were randomly selected for both blood and urine hcmv - dna tests ( figure 1b ) , and 25 hcmv - igg positive parturients were randomly selected for urine hcmv - dna tests ( figure 1c ) . mononuclear cells were isolated from the blood samples using tficoll separation solution ( shanghai hua jing biotech company ) . the urine samples were centrifuged for 10 minutes at 1,500 rpm and then the sediment was collected . the dna from mononuclear cells and from the sediment of urine samples were extracted using a dna extraction kit according to the manufacturer s instructions . quantitative real - time reverse transcription - pcr ( qrt - pcr ) was performed to determine cmv using taqman probe and roche light cycler fluorescence pcr detector . the blood samples were centrifuged at 1000 g for 10 minutes to separate serum . then , the serum samples were used to detect the hcmv - igm and hcmv - igg levels by colloidal gold labeled immuno - chromatographic test kit ( daan gene co. , ltd . statistical analysis of data was performed using spss 19.0 software ( statistical package for the social sciences ) . chi - square test was used to compare the percentage values between two groups ; p<0.05 was considered statistically significant . as shown in table 1 , 13.0% ( 6/46 ) of blood samples were hcmv - dna positive . however , urine samples showed a higher positive rate of 67.5% ( 133/197 ) ( p<0.001 ) . combined , the ratio of cmv infection in the wheezing infants was 57.2% ( 139/243 ) . serum hcmv - specific igm and igg levels in the wheezing infants were determined by colloidal gold labeled immuno - chromatographic test kit . the results showed that 6.2% ( 15/243 ) and 80.0% ( 190/243 ) of samples were positive for hcmv igm and igg antibodies , respectively ( table 2 ) . the result of mcnemar tests showed that the hcmv igg positive rate was higher than the igm positive rate in wheezing infants , and wheezing infants with igm positive were not simultaneously igg positive ( p<0.001 ) . to determine the correlation between hcmv - igg and urine - hcmv - dna , 10 wheezing infants who were positive for hcmv - igg the results showed that among the 10 igg - positive samples , only 20% ( 2/10 ) of the blood samples positively detected the dna of cmv . however , cmv dna was detected in urine for all the igg positive samples ( table 3 ) . a total of 3,000 blood samples from parturients were collected to detect hcmv - igm and hcmv - igg levels . as shown in table 4 , 80% ( 2,400/3,000 ) of samples were positive for hcmv - igg antibody . however , none of the samples were positive for hcmv - igm antibody . then 25 hcmv - igg positive parturients were randomly selected for detection of urine - hcmv - dna to determine the correlation of serum hcmv - igg with urine hcmv - dna in parturients . the results showed that hcmv dna could not be detected in the urine samples of the 25 hcmv - igg - positive parturients . as shown in table 1 , 13.0% ( 6/46 ) of blood samples were hcmv - dna positive . however , urine samples showed a higher positive rate of 67.5% ( 133/197 ) ( p<0.001 ) . combined , the ratio of cmv infection in the wheezing infants was 57.2% ( 139/243 ) . serum hcmv - specific igm and igg levels in the wheezing infants were determined by colloidal gold labeled immuno - chromatographic test kit . the results showed that 6.2% ( 15/243 ) and 80.0% ( 190/243 ) of samples were positive for hcmv igm and igg antibodies , respectively ( table 2 ) . the result of mcnemar tests showed that the hcmv igg positive rate was higher than the igm positive rate in wheezing infants , and wheezing infants with igm positive were not simultaneously igg positive ( p<0.001 ) . to determine the correlation between hcmv - igg and urine - hcmv - dna , 10 wheezing infants who were positive for hcmv - igg the results showed that among the 10 igg - positive samples , only 20% ( 2/10 ) of the blood samples positively detected the dna of cmv . however , cmv dna was detected in urine for all the igg positive samples ( table 3 ) . a total of 3,000 blood samples from parturients were collected to detect hcmv - igm and hcmv - igg levels . as shown in table 4 , then 25 hcmv - igg positive parturients were randomly selected for detection of urine - hcmv - dna to determine the correlation of serum hcmv - igg with urine hcmv - dna in parturients . the results showed that hcmv dna could not be detected in the urine samples of the 25 hcmv - igg - positive parturients . cmv is detected in saliva , semen , urine , emulsion and cervical secretions of infected patients and asymptomatic patients with latent infections . most cmv infected patients had latent infections , and congenital cmv infection could lead to neurological disability in children . thus , it is particularly important for early diagnosis as well as monitoring and treatment of cmv infection . in this study , we included 243 wheezing infants and found that the positive rate of serum hcmv - igm was significantly lower than that of serum hcmv - igg . then , 10 samples which were positive for hcmv - igg were randomly selected for the analysis of hcmv - dna in blood and urine to determine the correlation between hcmv - igg and hcmv - dna . the results indicated that there was a correlation between hcmv - igg and urine - hcmv - dna of wheezing infants . furthermore , hcmv might be a cause of wheezing for infants with a detection rate of 80% by serum hcmv - igg testing and 67.5% by urine - hcmv - dna testing . however , hcmv - dna could not be detected in the urine of the 25 hcmv - igg - positive parturients . the difference in results between parturients and wheezing infants suggested that infants were more susceptible to cmv than parturients . because kidney is a major target organ for cmv , once an infection occurs , a permanent latent infection will formed and exist for life . therefore , urine - positive hcmv - dna is not used as the measure for active cmv infection . positive tests for hcmv - dna in serum and plasma were considered as sign of active cmv infection as reported in chinese journal of pediatrics in 2012 . the immunological basis of asthma is an immune reaction mediated by th2 cells ; the airway chronic allergic inflammation mainly involves mast cells and eosinophils . th2 cells are also the predominant immunological cells for viral infection of infant wheezing , such as cmv infection . with rsv infection , the level of il - l0 secreted by dendritic cells declines , which leads to a th2 cell dominant immune response . with influenza virus ( ifz ) infection , dendritic cells secrete sufficient il-10 to inhibit the th2 response , and then the thl immune response is dominant . il-12 secreted by dendritic cells can promote a thl response , but inhibit th2 response . in addition , clinical studies have shown that the level of secreted il - l2 is inversely proportional to the degree of breathing   immune response caused by viral infection is influenced by a variety of factors . whether hcmv can inhibit or promote th2 response similar to rsv infection remains unknown , and should be verified in future experiments . urine - hcmv - dna test results were associated with serum hcmv - igg test results in wheezing infants but not parturients . the difference in the results for parturients compared to infants illustrates that infants but not parturients might be susceptible to hcmv infection .
backgroundthe aim of this study was to investigate the involvement of cmv infection in wheezing infants and the association between cmv - dna and immunoglobulins ( igs).material / methodsa total of 243 wheezing infants and 3,000 parturients were enrolled in this study . 
 the infants were randomly grouped to receive blood hcmv - dna tests ( n=46 ) or urine hcmv - dna tests ( n=197 ) . 
 furthermore , all participants had serum cmv - specific igm and igg testing . afterwards , 10 hcmv - igg positive infants were randomly selected for simultaneous blood and urine hcmv - dna tests , and 25 hcmv - igg positive puerperants were randomly selected for urine hcmv - dna tests.resultsthe detection rate of urine hcmv - dna was significantly higher than that of blood hcmv - dna ( 67.5% vs. 13.0% , p<0.001 ) . 
 fifteen ( 6.2% ) and 190 ( 80.0% ) infants showed positive cmv - specific igm and igg results ( p<0.001 ) , respectively . among the 10 hcmv - igg positive infants tested further , only two infants had positive hcmv - dna blood tests , while all of the 10 infants had positive hcmv - dna urine tests . 
 however , hcmv - dna was not detected in the urine of the 25 randomly selected parturients positive for hcmv-igg.conclusionscmv infection may be one of the causes of wheezing in infants ; cmv infection can be detected by urine - hcmv - dna and serum hcmv - igg testing . 
 infants were more susceptible to cmv infection than parturients .