What is the True Incidence of Measles
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《美国医学杂志》
1 Envirosafe Training and Consultants, PO Box 114022, Pittsburgh, PA 15239, USA
2 Department of Environmental Medicine and Public Health, University of Padova, Via Giustiniani, 2-35128 Padova, Italy
3 University of the Sciences, 600 South 43rd Street, Philadelphia, PA 19104, USA
Ray et al[1] reported on the incidence of measles in the Kolkata area (Culcutta) of India for the time period 2000. They report a lower incidence rate than previously reported for Surat, although higher than other compared locations (i.e. Western Rajashthan). As suggested by the authors, some of this difference is a result of variation in occurrence of measles in the compared populations, immunization and Vitamin A deficiency. In this and other studies [2] that utilize counting of cases it is likely that there is a large undercount.[ 3] We would like to suggest that there is a better method for counting[4], which is the capture recapture method (CRM) (also called mark-capture method). This method utilizes two or more sources of reported cases and allows determination of the undercount (missed cases that would be countable).[5] It has been previously reported that the CRM is a more accurate estimator of the true number of cases or events.[4]
Since the authors collected one source, it would not be difficult to obtain others (e.g. hospital, public health and/ or clinic records, institutional records on notification of infectious diseases) for comparison to estimate the incidence of measles. There are requirements for sources (e.g. independence) for the CRM; however, based on the information provided by the authors, these sources (e.g. hospital records) do exist. The CRM will also provide a confidence interval for the count.[5] It is also possible that the authors could perform re-sampling (mark-capture) as the second source.
Unfortunately, the CPM has not been widely used in epidemiological studies, although is commonly employed for counting more difficult populations (e.g. wildlife).[6] Hopefully its use in counting numbers (cases) in epidemiology will become more widespread, especially since it is suggested as "gold standard for counting cases". [4,7] The CRM should be considered a more accurate counting method as compared to traditional practices used by the epidemiologists and others. [4,5
References
1. Ray SK, Mallik S, Munsi AK, Mitra SP, Baur B, Kumar S. Epidemiological study of measles in slum areas of Kolkata. Indian J Pediatr 2004; 71: 583-586.
2. Kapil U, Sethi V, Goindi G, Pathak P, Singh P. Estimation of iodine deficiency disorders in Delhi. Indian J Pediatr 2004; 71: 211-212
3. Lange JH, LaPorte RE. Severe acute respiratory syndrome: capture-recapture methods should be used to count how many cases of SARS really exist. (Letter). Brit Med J 2003; 326: 1396.
4. Lange JH, LaPorte RE, Talbott EO, Chang YF. Capture-recapture method: the gold standard for incidence and prevalence. (Letter ) New Zealand Med J 2003; 20: 116.
5. LaPorte RE, McCarty DJ, Tull ES, Tajima N. Counting birds, bees and NCDs. Lancet (Letter) 1992; 339: 494-495.
6. LeCren ED. A note on the history of mark-capture population estimates. J Animal Ecology 1965; 34: 453-454.
7. Lange JH, Chang YF, LaPorte RE. Talbott EO, Wang M, Mastrangelo G. Finding hazardous waste sites: evaluation using the capture-recapture methods. Bull Environ Contam Tox 2004; 72 : 1182-1186(Lange John H, Mastrangelo)
2 Department of Environmental Medicine and Public Health, University of Padova, Via Giustiniani, 2-35128 Padova, Italy
3 University of the Sciences, 600 South 43rd Street, Philadelphia, PA 19104, USA
Ray et al[1] reported on the incidence of measles in the Kolkata area (Culcutta) of India for the time period 2000. They report a lower incidence rate than previously reported for Surat, although higher than other compared locations (i.e. Western Rajashthan). As suggested by the authors, some of this difference is a result of variation in occurrence of measles in the compared populations, immunization and Vitamin A deficiency. In this and other studies [2] that utilize counting of cases it is likely that there is a large undercount.[ 3] We would like to suggest that there is a better method for counting[4], which is the capture recapture method (CRM) (also called mark-capture method). This method utilizes two or more sources of reported cases and allows determination of the undercount (missed cases that would be countable).[5] It has been previously reported that the CRM is a more accurate estimator of the true number of cases or events.[4]
Since the authors collected one source, it would not be difficult to obtain others (e.g. hospital, public health and/ or clinic records, institutional records on notification of infectious diseases) for comparison to estimate the incidence of measles. There are requirements for sources (e.g. independence) for the CRM; however, based on the information provided by the authors, these sources (e.g. hospital records) do exist. The CRM will also provide a confidence interval for the count.[5] It is also possible that the authors could perform re-sampling (mark-capture) as the second source.
Unfortunately, the CPM has not been widely used in epidemiological studies, although is commonly employed for counting more difficult populations (e.g. wildlife).[6] Hopefully its use in counting numbers (cases) in epidemiology will become more widespread, especially since it is suggested as "gold standard for counting cases". [4,7] The CRM should be considered a more accurate counting method as compared to traditional practices used by the epidemiologists and others. [4,5
References
1. Ray SK, Mallik S, Munsi AK, Mitra SP, Baur B, Kumar S. Epidemiological study of measles in slum areas of Kolkata. Indian J Pediatr 2004; 71: 583-586.
2. Kapil U, Sethi V, Goindi G, Pathak P, Singh P. Estimation of iodine deficiency disorders in Delhi. Indian J Pediatr 2004; 71: 211-212
3. Lange JH, LaPorte RE. Severe acute respiratory syndrome: capture-recapture methods should be used to count how many cases of SARS really exist. (Letter). Brit Med J 2003; 326: 1396.
4. Lange JH, LaPorte RE, Talbott EO, Chang YF. Capture-recapture method: the gold standard for incidence and prevalence. (Letter ) New Zealand Med J 2003; 20: 116.
5. LaPorte RE, McCarty DJ, Tull ES, Tajima N. Counting birds, bees and NCDs. Lancet (Letter) 1992; 339: 494-495.
6. LeCren ED. A note on the history of mark-capture population estimates. J Animal Ecology 1965; 34: 453-454.
7. Lange JH, Chang YF, LaPorte RE. Talbott EO, Wang M, Mastrangelo G. Finding hazardous waste sites: evaluation using the capture-recapture methods. Bull Environ Contam Tox 2004; 72 : 1182-1186(Lange John H, Mastrangelo)