To the Editor: Parker et al. (Aug. 3 issue)1 describe the largestdocumented outbreak of measles in the United States since 1996,which is of considerable epidemiologic interest. It is surprisingthat few of the cases were confirmed by laboratory analysis,particularly one of the two involving "vaccine failure." Couldthe authors explain why, with the availability of noninvasivetesting methods, more patients were not tested? It is also unclearhow local investigators identified the cases and whether anyconsideration was given to the possibility of asymptomatic infection,since there is evidence that measles may circulate in vaccinatedpopulations and cause subclinical infection.2
Erika F. Duffell, M.F.P.H., M.P.H. Greater Manchester Health Protection Unit Manchester M30 0NJ, United Kingdom
References
Parker AA, Staggs W, Dayan GH, et al. Implications of a 2005 measles outbreak in Indiana for sustained elimination of measles in the United States. N Engl J Med 2006;355:447-455. [Erratum, N Engl J Med 2006;355:1184.] [Free Full Text]
Vardas E, Kreis S. Isolation of measles virus from a naturally-immune, asymptomatically re-infected individual. J Clin Virol 1999;13:173-179. [CrossRef][Web of Science][Medline]
The authors reply: We obtained laboratory confirmation for at least one patient in 9 of 11 families infected with measles.Among these 9 families, 14 of 20 patients had disease that wasconfirmed by laboratory analysis. The remaining two families(with 10 and 4 patients, respectively) declined to have specimenscollected from all family members. The parents of the patientwho had measles despite receiving two doses of vaccine declinedto have specimens collected from any of their children exceptone whose disease was confirmed by laboratory testing duringhospitalization. All patients had classic clinical symptomsof measles that appeared after the appropriate incubation periodafter exposure to a patient with laboratory-confirmed disease.The percentage of cases that were confirmed by laboratory testingin the Indiana outbreak (41%) was similar to that in other outbreaksamong groups of persons who had declined to receive vaccination.1,2
Case finding involved contacting persons with a known exposureto measles, physician alerts, and media releases. Although theasymptomatic spread of measles could potentially occur, allbut one patient had an identified source. This patient workedin a hospital where patients with measles had been treated within14 days before the onset of her symptoms. Thus, we believe thatasymptomatic transmission was unlikely to have played a majorrole in the Indiana outbreak.
Amy A. Parker, M.S.N., M.P.H. Centers for Disease Control and Prevention Atlanta, GA 30333
Wayne Staggs, M.S. Indiana State Department of Health Indianapolis, IN 46204
Gustavo H. Dayan, M.D. Centers for Disease Control and Prevention Atlanta, GA 30333
References
Hanratty B, Holt T, Duffell E, et al. UK measles outbreak in non-immune anthroposophic communities: the implications for the elimination of measles from Europe. Epidemiol Infect 2000;125:377-383. [CrossRef][Medline]
Siedler A, Tischer A, Mankertz A, Santibanez S. Two outbreaks of measles in Germany 2005. Euro Surveill 2006;11:131-134. [Medline]
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