[5] Loew A, Thibeault DW. A new and safe method to control the depth of endotracheal intubation in neonates. Pediatrics 1974;54:506-8. [6] Coldiron JS. Estimation of nasotracheal tube length in neonates, Pediatrics 1968;41:823-8. [7] Kuhns LR, Poznanski AK. Endotracheal tube position in the infant. J Pediatr 1971;78:991-6. [8] Bednarek FJ, Kuhns LR. Endotracheal tube placement in infants determined by suprasternal palpation: A new technique. Pediatrics 1975; 56:224-9. [9] Bloch ED, Ossey K, Ginsberg B. Tracheal intubation in children: A new method for assuring correct depth of tube placement. Anesth Analg 1988;67:590-2. [10] Roberts JT. Fundamentals of tracheal intubation. In: Endotracheal tubes. New York: Grune and Stratton, 1983;35-45.
SUBACUTE
SCLEROSING
showing declining rates of developing SSPE by increasing year of birth. It would also be of interest to analyze the cases of SSPE in recent years by year of measles infection. Physicians caring for adolescents have frequently asked whether administration of measles vaccine to children who have already had measles may increase the risk of SSPE. Data from the controlled study revealed that SSPE children were less likely to have received measles vaccine after natural measles than were controls [2]. Thus, administration of measles vaccine to children with a prior history of measles or serologic evidence of measles should not alter their already established but low risk (5-22 cases of SSPE per million measles infections) of developing SSPE [3]. Neal A. Halsey, MD John F. Modlin, MD Johns Hopkins University Medical Institutes Baltimore, Maryland
PANENCEPHALITIS
To the Editor: Dyken et al. recently reported interesting findings from the National Registry for subacute sclerosing panencephalitis (SSPE) [ 1]. We disagree with Dyken et al. with their interpretation of some of the data. The presentation of the data implied that a causal relationship between measles vaccine and SSPE has been established. This, in fact, is not the case. We call attention to investigations conducted through the National Registry prior to his assuming responsibility for maintaining this valuable data source [2,3]. The association between SSPE and measles vaccination can be addressed most appropriately by comparing children with SSPE to appropriate controls. A case-control study comparing 49 children with SSPE to age- and sex-matched community and hospital controls was reported in 1980 [2]. This study revealed a strong inverse association between measles vaccine and SSPE. Children with SSPE were significantly (P < 0.01) less likely to have received measles vaccine than the controls. As demonstrated in Table 1 of Dyken et al.'s report, some children with SSPE have received measles vaccine either after having had natural measles or without a history of natural measles [ 1]; however, the proportion of SSPE children who had received measles vaccine was significantly smaller than the proportion of controls who had received measles vaccine regardless of the history of measles. Moreover, all SSPE children and most controls who had no history of having had measles or of receiving measles vaccine had serologic evidence of prior measles infections. Several SSPE children who did not have a history of measles had been exposed to a sibling or close friend with measles. Some of these children had received immune serum globulin after exposure to measles. These children undoubtedly had subclinical or modified measles illnesses. This is not surprising since before measles vaccines were available 15-20% of children without a history of measles had serologic evidence of having been infected with measles [4,5]. It is very likely that most or all of the SSPE children reported by Dyken et al. in the past 10 years with no history of measles also had undiagnosed measles infections. The shorter interval between having received measles vaccine and onset of SSPE as compared to the interval between measles and SSPE was also observed in the earlier studies [6]. Since having measles at less than 2 years of age is a risk factor for SSPE and many children in the United States receive measles vaccine when older than 2 years of age, this difference in an apparent "latent" period is likely to be a chance occurrence. There was no association between the age of measles vaccination and SSPE in the controlled study [2]. If measles vaccine was associated with SSPE and the interval was shorter than the interval for natural measles, then we should be seeing an increasing incidence of SSPE. The continuing decline in the incidence of SSPE reported by Dyken et al. is reassuring and reinforces the conclusion that measles vaccine prevents measles and all of its complications. The longer latent period from measles to onset of SSPE noted in recent years is also of interest and consistent with the pattern that was observed a decade earlier [3]. This pattern is best shown by a cohort analysis
References [1] Dyken PR, Cunningham SC, Ward CL. Changing character of subacute sclerosing panencephalitis in the United States. Pediatr Neurol 1989;5:339-41. [2] Halsey NA, Modlin JF, Jabbour JT, Dubey L, Eddins DL, Ludwig DD. Risk factors in subacute sclerosing panencephalitis: A case-control study. Am J Epidemiol 1980;4:415-24. [3] Halsey NA, Modlin JF, Jabbour JT. Subacute sclerosing panencephalitis: An epidemiologic review. In: Stevens JG, Todoro GJ, Fox CF, eds. Persistent viruses. Proceedings of the ICN-UCLA Symposia on Molecular and Cellular Biology, vol XI. New York: Academic Press, 1978;101-14. [4] Krugman S, Giles JP, Friedman H, Stone S. Studies on immunity to measles. J Pediatr 1965;66:471-88. [5] Krugman S, Giles JP, Jacobs AM, Friedman H. Studies with live attenuated measles-virus vaccine. Am J Dis Child 1962;103:353-6. [6] Modlin JF, Jabbour JT, Witte JJ, Halsey NA. Epidemiologic studies of measles, measles vaccine, and subacute sclerosing panencephalitis. Pediatrics 1977;59:505-12.
To the Editor: The letter by Halsey and Modlin in response to our article [ 1] was read with great interest. Even though the past publications by the authors on SSPE are well known to me, I found the brief letter, which was informative as well as critical, to be very educational. Since measles vaccine was introduced, there has been a dramatic decline in the incidence of SSPE in the United States, as reported to the Registry, whether associated with natural measles, measles vaccine, or neither. Halsey and Modlin stated that our article "implied that a causal relationship between measles vaccine and SSPE has been established." This was not what was implied. We simply reported our statistics that indicated there was a greater decline in SSPE in those who gave a history of natural measles than in those who had a history only of measles vaccination. A third group known to have natural measles and measles vaccine was also included in the data. These data covered the entire population of patients reported to the United States Registry on SSPE which was the basis of Halsey and Modlin's studies on SSPE, plus 200 more patients reported since their studies were completed. There were no conclusions drawn about the causal relationship of measles vaccine and SSPE. I am essentially in agreement with the other comments of Drs. Halsey and Modlin. Paul R. Dyken, MD University of South Alabama Mobile, Alabama Reference [1] Dyken PR, Cunningham SC, Ward CL. Changing character of subacute sclerosing panencephalitis in the United States. Pediatr Neurol 1989;5:339-41.
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SUBACUTE
SCLEROSING
showing declining rates of developing SSPE by increasing year of birth. It would also be of interest to analyze the cases of SSPE in recent years by year of measles infection. Physicians caring for adolescents have frequently asked whether administration of measles vaccine to children who have already had measles may increase the risk of SSPE. Data from the controlled study revealed that SSPE children were less likely to have received measles vaccine after natural measles than were controls [2]. Thus, administration of measles vaccine to children with a prior history of measles or serologic evidence of measles should not alter their already established but low risk (5-22 cases of SSPE per million measles infections) of developing SSPE [3]. Neal A. Halsey, MD John F. Modlin, MD Johns Hopkins University Medical Institutes Baltimore, Maryland
PANENCEPHALITIS
To the Editor: Dyken et al. recently reported interesting findings from the National Registry for subacute sclerosing panencephalitis (SSPE) [ 1]. We disagree with Dyken et al. with their interpretation of some of the data. The presentation of the data implied that a causal relationship between measles vaccine and SSPE has been established. This, in fact, is not the case. We call attention to investigations conducted through the National Registry prior to his assuming responsibility for maintaining this valuable data source [2,3]. The association between SSPE and measles vaccination can be addressed most appropriately by comparing children with SSPE to appropriate controls. A case-control study comparing 49 children with SSPE to age- and sex-matched community and hospital controls was reported in 1980 [2]. This study revealed a strong inverse association between measles vaccine and SSPE. Children with SSPE were significantly (P < 0.01) less likely to have received measles vaccine than the controls. As demonstrated in Table 1 of Dyken et al.'s report, some children with SSPE have received measles vaccine either after having had natural measles or without a history of natural measles [ 1]; however, the proportion of SSPE children who had received measles vaccine was significantly smaller than the proportion of controls who had received measles vaccine regardless of the history of measles. Moreover, all SSPE children and most controls who had no history of having had measles or of receiving measles vaccine had serologic evidence of prior measles infections. Several SSPE children who did not have a history of measles had been exposed to a sibling or close friend with measles. Some of these children had received immune serum globulin after exposure to measles. These children undoubtedly had subclinical or modified measles illnesses. This is not surprising since before measles vaccines were available 15-20% of children without a history of measles had serologic evidence of having been infected with measles [4,5]. It is very likely that most or all of the SSPE children reported by Dyken et al. in the past 10 years with no history of measles also had undiagnosed measles infections. The shorter interval between having received measles vaccine and onset of SSPE as compared to the interval between measles and SSPE was also observed in the earlier studies [6]. Since having measles at less than 2 years of age is a risk factor for SSPE and many children in the United States receive measles vaccine when older than 2 years of age, this difference in an apparent "latent" period is likely to be a chance occurrence. There was no association between the age of measles vaccination and SSPE in the controlled study [2]. If measles vaccine was associated with SSPE and the interval was shorter than the interval for natural measles, then we should be seeing an increasing incidence of SSPE. The continuing decline in the incidence of SSPE reported by Dyken et al. is reassuring and reinforces the conclusion that measles vaccine prevents measles and all of its complications. The longer latent period from measles to onset of SSPE noted in recent years is also of interest and consistent with the pattern that was observed a decade earlier [3]. This pattern is best shown by a cohort analysis
References [1] Dyken PR, Cunningham SC, Ward CL. Changing character of subacute sclerosing panencephalitis in the United States. Pediatr Neurol 1989;5:339-41. [2] Halsey NA, Modlin JF, Jabbour JT, Dubey L, Eddins DL, Ludwig DD. Risk factors in subacute sclerosing panencephalitis: A case-control study. Am J Epidemiol 1980;4:415-24. [3] Halsey NA, Modlin JF, Jabbour JT. Subacute sclerosing panencephalitis: An epidemiologic review. In: Stevens JG, Todoro GJ, Fox CF, eds. Persistent viruses. Proceedings of the ICN-UCLA Symposia on Molecular and Cellular Biology, vol XI. New York: Academic Press, 1978;101-14. [4] Krugman S, Giles JP, Friedman H, Stone S. Studies on immunity to measles. J Pediatr 1965;66:471-88. [5] Krugman S, Giles JP, Jacobs AM, Friedman H. Studies with live attenuated measles-virus vaccine. Am J Dis Child 1962;103:353-6. [6] Modlin JF, Jabbour JT, Witte JJ, Halsey NA. Epidemiologic studies of measles, measles vaccine, and subacute sclerosing panencephalitis. Pediatrics 1977;59:505-12.
To the Editor: The letter by Halsey and Modlin in response to our article [ 1] was read with great interest. Even though the past publications by the authors on SSPE are well known to me, I found the brief letter, which was informative as well as critical, to be very educational. Since measles vaccine was introduced, there has been a dramatic decline in the incidence of SSPE in the United States, as reported to the Registry, whether associated with natural measles, measles vaccine, or neither. Halsey and Modlin stated that our article "implied that a causal relationship between measles vaccine and SSPE has been established." This was not what was implied. We simply reported our statistics that indicated there was a greater decline in SSPE in those who gave a history of natural measles than in those who had a history only of measles vaccination. A third group known to have natural measles and measles vaccine was also included in the data. These data covered the entire population of patients reported to the United States Registry on SSPE which was the basis of Halsey and Modlin's studies on SSPE, plus 200 more patients reported since their studies were completed. There were no conclusions drawn about the causal relationship of measles vaccine and SSPE. I am essentially in agreement with the other comments of Drs. Halsey and Modlin. Paul R. Dyken, MD University of South Alabama Mobile, Alabama Reference [1] Dyken PR, Cunningham SC, Ward CL. Changing character of subacute sclerosing panencephalitis in the United States. Pediatr Neurol 1989;5:339-41.
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