Measles epidemic attributed to inadequate vaccination coverage—Campania, Italy, 2002

Morbidity and Mortality Weekly Report, Oct 31, 2003 by Ciofi degli Atti, F Fabi, S Salmaso, D Biol, R Pizzuti, E de Campora

In Italy, measles has been a mandatory reportable disease for >100 years. During the prevaccination era, approximately 25,000-90,000 cases were reported annually. During the late 1980s and 1990s, incidence declined with increasing measles vaccination coverage, but measles epidemics continued to occur periodically, most recently during 1995-1997 (Figure 1). In early 2002, measles incidence increased sharply; the area most affected was Campania (2001 population: approximately 5,782,000, including 1,100,000 children aged <15 years), a large region in southern Italy (Figure 2). In 2001, estimated measles vaccination coverage for the 1998 Campania birth cohort was 65% (1). Regional health authorities and the National Institute of Health investigated the measles outbreak in Campania. This report summarizes the preliminary results of the investigation, which attributed the epidemic to inadequate vaccination coverage. A coordinated effort is needed to interrupt measles transmission in Italy.

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To monitor the incidence of measles and other vaccine-preventable diseases among children aged <15 years, in January 2000, a national pediatric sentinel surveillance system (SPES) was initiated, covering approximately 4% of children aged <15 years (2). Children are tracked by National Health System primary-care pediatricians who participate voluntarily. These pediatricians report cases of measles and other vaccine-preventable diseases diagnosed during the preceding month by e-mail or fax to the National Institute of Health in Rome. SPES uses a standard clinical case definition for measles (3), but laboratory confirmation is not required. Information collected on each case includes date of birth, date of illness onset, sex, and vaccination status. Reporting on presence or absence of cases is required, and the monthly incidence rate is calculated by using the number of reported cases as the numerator and the total patient population cared for by the pediatricians participating in the surveillance system during that month as the denominator.

Data on measles-associated hospitalizations that occurred during January-July 2002 were collected by reviewing discharge records of the five main regional hospitals with infectious diseases units. For each patient, information about sex, date of birth, admission and discharge dates, and diagnosis at discharge was collected. Information on regional vaccination coverage was derived from a survey conducted during 2000-2001 of a sample of 12,647 children aged 24-36 months who were born in 1998 (1).

In 2002, an average of 51 pediatricians in Campania participated in SPES, covering an estimated 41,888 children (3.8% of the regional total). A total of 1,571 measles cases were reported, resulting in an annual incidence of 3,750 cases per 100,000 children aged <15 years. The majority (1,543 [98%]) of cases occurred during January-July, with a peak in May (Figure 3).

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Incidence increased with age, from 1,088 per 100,000 in children aged <1 year to 2,413 in those aged 1-4 years, 3,506 in those aged 5-9 years, and 5,592 in those aged 10-14 years. Incidences were highest in the provinces of Naples and Caserta, the areas with the lowest measles vaccination coverage (Table).

Vaccination status was known for 1,543 (98%) of the reported patients; of these, 101 (7%) were vaccinated, and the remainder were unvaccinated. The number of administered doses was reported for 72 (71%) children; 70 were vaccinated with 1 dose, and two with 2 doses. The proportion of vaccinated patients aged [greater than or equal to] 1 year decreased with age, from 10.5% among children aged 1-4 years to 5.5% among children aged 5-14 years.

Hospital record review identified 594 measles-associated hospitalizations that occurred during January-July 2002. Of these, 469 (79%) occurred among children aged <15 years, and 44 (7%) in infants aged <1 year. Diagnosis at discharge was available for 425 (91%) children; 99 (23%) had respiratory complications (pneumonia/bronchopneumonia), 12 (3%) encephalitis, and two (1%) thrombocytopenia. Of the remaining children, 15 (4%) had other complications, and 297 (70%) had uncomplicated measles. Three children (aged 6 months, 4 years, and 10 years, respectively) died. The remaining 125 (21%) cases of identified measles-associated hospitalizations occurred among persons aged >15 years, including three additional cases of encephalitis and one measles-associated death attributed to respiratory failure in a person aged 29 years.

Regional health authorities recommended 1) vaccinating persons exposed to patients in family and school settings; 2) offering measles, mumps, and rubella (MMR) vaccine to all persons who had not been vaccinated or who did not have a history of measles; and 3) temporarily lowering the age of MMR vaccination to 6 months, with subsequent revaccination after 1 year of those children vaccinated at age 6-12 months. However, these measures did not stop the epidemic, which spread subsequently to other areas. Approximately 1,000 additional cases were reported to SPES from other regions, and the national annual attack rate in children aged <15 years was 738 per 100,000. The most affected regions were central and southern Italy, with regional incidences seven to 36 times higher than in northern Italy. After an apparent decline in reported incidence during August-December 2002, the epidemic continued during the first half of 2003, affecting the southern regions of Abruzzo, Puglia, and Calabria (Figure 2) (4).