Current Trends Measles -- Puerto Rico, 1993, and the Measles Elimination Program

In the Commonwealth of Puerto Rico, a resurgence of measles peaked in 1990 when 1805 cases (51.3 cases per 100,000 population) and 12 measles-related deaths were reported. This report summarizes the persistence of measles transmission in Puerto Rico in 1993 and describes the Puerto Rico Measles Elimination Program.

Because of similarities in clinical features of measles and dengue (which is endemic in Puerto Rico {1}), since 1991 only measles cases serologically confirmed by enzyme-linked immunosorbent assay have been reported to CDC. In 1993, 355 measles cases were reported (10.1 per 100,000). Cases were reported from each region of Puerto Rico (Figure_1); the largest outbreaks were reported from Arecibo (219 cases {53.7 per 100,000}), Ponce (46 {8.2}), and Metropolitan (including San Juan) (31 {3.7}). Confirmed cases were reported in each month; nearly half of all cases occurred during April (48 cases), May (77), and June (52); fewer than 10 cases occurred each month during October-December.

Most (254 {72%}) cases occurred among preschool-aged children (i.e., aged 0-5 years); 116 (33%) occurred among infants (i.e., aged less than 12 months). Among the 248 (70%) persons with measles for whom vaccination status was known, 149 (60%) were unvaccinated; these unvaccinated persons constituted 93% of infants, 56% of children aged 1-5 years, 2% of school-aged children, and 64% of adults (Table_1).

From 1983 to 1990, Puerto Rico required one dose of measles-mumps-rubella vaccine (MMR) for school entry, and annual audits during 1990-1992 indicated approximately 95% coverage among children in all grades. Since 1990, two doses of MMR have been required for school entry, and annual audits during 1991-1992 indicated approximately 90% coverage with two doses among children entering school. In 1990, Puerto Rico lowered the recommended age for routine vaccination with MMR to 12 months. Vaccination coverage with one dose of MMR by 24 months (estimated by retrospective studies of children entering school in 1992) was 69%.

To eliminate indigenous measles transmission in Puerto Rico by 1996, the Puerto Rico Department of Health (PRDH) is conducting the Puerto Rico Measles Elimination Program, an islandwide effort comprising a mass vaccination campaign, increased measles surveillance, and aggressive outbreak control.

Reported by: C Feliciano, MD, Secretary of Health; E Pintado Diaz, MD, Central Office of AIDS and Communicable Diseases Affairs; E Calderon, V Rodriguez, Immunization Program; C Deseda, MD, Measles Elimination Program; C Rodriguez, Div of Epidemiology; JV Rullan, MD, Commonwealth Epidemiologist, Puerto Rico Dept of Health. National Immunization Program; Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Elimination of indigenous measles in the United States by 1996 is a goal of the Childhood Immunization Initiative (2). The approach adopted in Puerto Rico to meet this objective is based on a measles-elimination strategy advocated by the Pan American Health Organization (PAHO). This strategy, implemented by 14 Latin American countries and all 17 English-speaking Caribbean countries, supplements routine vaccination with mass vaccination campaigns for children aged less than 15 years regardless of previous vaccination status and enhances surveillance for febrile rash illness. Since September 1991, no confirmed indigenous measles cases have been reported from the English-speaking Caribbean countries or Cuba (Expanded Program on Immunization, PAHO, unpublished data, 1994).

Because effective school vaccination laws have resulted in high (greater than 90%) MMR coverage among all school-aged children in Puerto Rico, PRDH will focus its mass vaccination campaign on preschool-aged children, among whom most (72%) of the recent cases have occurred. This campaign, scheduled for March 16-19, 1994, will target the approximately 353,000 children in Puerto Rico aged 6 months-5 years, regardless of previous measles vaccination history. In addition, health-care providers will assess vaccination status of children for whom records are available for oral poliovirus vaccine, diphtheria and tetanus toxoids and pertussis vaccine, and Haemophilus influenzae type b vaccine and will administer needed vaccines. Following the campaign, PRDH will conduct a population-based evaluation of the vaccination coverage achieved.

Other elements of the measles elimination program in Puerto Rico are to increase measles surveillance and to implement aggressive outbreak control. PRDH will establish a febrile rash illness reporting system. All health-care providers will be encouraged to promptly report to PRDH every case of febrile rash illness, which will be investigated within 24 hours of report. Measles surveillance will continue to be coordinated with the PRDH Community Hygiene Division (which conducts dengue surveillance) and CDC's Dengue Branch, Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, in San Juan to provide additional laboratory diagnosis of cases of rash illness. Private laboratories will be requested to notify PRDH on receipt of any specimen submitted for measles serology. A case-response protocol will enable PRDH to implement outbreak-control measures as soon as a diagnosis of measles is considered likely -- ideally within 3 days of rash onset. Control measures will include enhanced case investigation, contact tracing, and vaccination of contacts.

Because measles may circulate independently among older vaccinated persons (without a reservoir of susceptible preschool-aged children to sustain transmission), measles circulation in Puerto Rico could persist despite a successful mass vaccination campaign. Enhanced surveillance efforts will be needed to identify this trend and to stimulate development of additional strategies to interrupt transmission. In addition, continued efforts to improve timely vaccination of preschool-aged children will be necessary to maintain the high vaccination coverage level anticipated following the campaign.

References

1. Dietz VJ, Nieburg P, Gubler DJ, Gomez I. Diagnosis of measles by clinical case definition in dengue-endemic areas: implications for measles surveillance and control. Bull World Health Organ 1992;47:745-50.

2. CDC. Reported vaccine-preventable diseases -- United States, 1993, and the Childhood Immunization Initiative. MMWR 1994;43:57-60.

TABLE 1. Number and percentage of persons with reported measles for whom
vaccination status was known, by age group and vaccination status * -- Puerto Rico,
1993 +
==========================================================================================
                Vaccinated       Unvaccinated        Total cases
Age group      -----------       ------------       ------------
  (yrs)        No.     (%)       No.     (%)        No.     (%)
----------------------------------------------------------------
   <1            6    ( 7)       82     (93)        88     ( 35)
 1- 5           40    (44)       50     (56)        90     ( 36)
 6-18           44    (98)        1     ( 2)        45     ( 18)
 >=19            9    (36)       16     (64)        25     ( 10)

Total           99    (40)      149     (60)       248     (100)
----------------------------------------------------------------
* Excludes 107 persons with measles (28 were aged <1 year; 48, aged 1-5 years; 25, aged
  6-18 years; and 6, aged >=19 years) whose vaccination status was unknown.
+ Data are provisional.
==========================================================================================

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