From November 1998 to December 2000, 84
suspected measles cases were reported in Catalonia (6 090 040 inhabitants).
Of the 73 laboratory tested cases (87%), 20 showed IgM antibodies specific
to measles and 3 were epidemiologically linked to a confirmed case. Among
these 23 confirmed cases, 13 were indigenous, the last two cases reported
dating back from June 1999 and July 2000. These results confirm the success
of the measles elimination programme implemented in 1998 in Catalonia.
Background
Measles is a candidate disease for elimination, given that humans are
the only hosts of the virus, that subclinical cases are very rare, and
that an efficacious vaccine (offering 95% protection) is available (1).
As already shown in the United States, the transmission of indigenous
measles ceased in 1993, according to data from genetic analysis of isolated
measles virus (2-4,15).
In 1988 the Department of Health and Social Security of Catalonia, a
region of Spain, started a programme for the elimination of measles in
the region by the year 2000 (5-9). The incidence of measles infection
in Catalonia (estimated population 6 090 040) declined from 470 per 100
000 inhabitants in 1983 to 1.01/100 000 in 1997 (5) and 0.5/100 000 inhabitants
in 1999 (figure 1). In light of this, the public health authorities decided
in 1997 to introduce an individualised reporting status for measles (11-13).
The individualised report form provides information on clinical features
as well as details such as the name, telephone number, and address of
a patient, thus allowing a complete epidemiological study of each reported
case.
Methods
The final stage of the programme "Elimination of measles in Catalonia
by the year 2000)" began in November 1998. Three main strategies
were adopted.
a) Improvement of the immunisation status of the susceptible population
by giving the second dose of the measles-mumps-rubella (MMR) vaccine at
age 4 in the 1999 vaccine calendar instead of at age 11 as was set in
1988, and by a selective plan for administration of the second dose to
the cohorts born between 1990 and 1993, to ensure that all children were
properly vaccinated (10,14). Vaccine certificates are checked by the public
health department to verify the first and second doses of MMR vaccine
and to determine coverage of the second dose.
b) Enhanced epidemiological surveillance of suspected cases of the disease,
which includes prompt notification of the case by the attending physician
(within 24 hours of onset) to the public health department and active
follow up of the case and his or her contacts, with concise and exhaustive
collection of all epidemiological information relevant to the case. A
suspected case would be defined as a patient with clinical features of
measles virus infection (rash for more than three days, fever above 38,5°C,
cough and/or coryza and/or conjunctivitis) for whom the diagnosis has
not yet been confirmed by serological tests or by a relation to a laboratory
confirmed case. A laboratory confirmed case would be a suspected case
confirmed by specific serological test and/or isolation of measles virus
from urine specimens. An epidemiologically confirmed case would be a suspected
case related epidemiologically to a laboratory confirmed case of measles.
The epidemiological information collected includes clinical features,
immunisation status, travel, school attendance, and any other information
that might be useful to determine the source of transmission and probable
susceptible contacts.
Blood and urine specimens are collected from the 4th to 11th day after
the appearance of the rash either by staff belonging specifically to the
programme or by hospital or primary care staff. Laboratory determination
of specific IgM type antibodies by an indirect immunofluorescence method
is carried out immediately, and the case can thus be confirmed promptly.
If positive, the urine specimen is cultured on B95a cells to isolate the
virus for genetic analysis (3,4). With regard to its origin, a confirmed
case would be considered imported if the patient had been outside Catalonia
7 to 18 days before the onset of the exanthem or had had contact with
a suspected case from abroad. A case is defined as indigenous if there
is no epidemiological evidence of transmission from a foreign source.
c) Vaccination of the susceptible population who had contact with the
case (schoolmates, household contacts) and inquiries to see whether there
are unreported cases. Susceptible contacts would be all those younger
than 25 years who can not prove they have received two doses of MMR vaccine.
Results are assessed by surveillance of the morbidity during the years
in which the programme has been operative, from 1998 to 2000.
Results
Certifications of the second MMR vaccination dose collected from schools
and primary care centres showed a registered coverage of 85%.
According to the case definition, the number of suspected cases notified
between November 1998 and December 2000 was 84 (figure 2). Clinical specimens
were obtained from 73/84 (87%). Only 20 of these had positive IgM antibodies
to the measles virus, with 3 more being confirmed by epidemiological relation
to a laboratory confirmed case.
From the beginning of the programme on 1st November until 31st December
1998, 10 cases were reported. Only 6 of these could be analysed and were
confirmed as negative by laboratory assessment. Of the 49 cases reported
from January to December 1999, 44 were analysed and 17 confirmed as positive
for to anti-measles IgM antibodies. In addition, one was confirmed by
exposure to an outbreak. From January to December 2000, 25 cases were
reported of whom 23 were analysed. Only 3 of these cases were confirmed,
and 2 more considered confirmed because they were related to a laboratory
confirmed case.
Of the cases confirmed in 1999, 6/18 (33%) were proved by epidemiological
evidence to be imported. Four (80%) of the five cases confirmed in 2000
were proved to be imported by epidemiological evidence, and one case lives
in an urban area where most of the inhabitants are immigrants from Morocco,
Pakistan, and the Philippines, which leads us to suspect that this case
could also be imported. Thus no indigenous cases were confirmed from June
1999 to July 2000. From July to December 2000 there was only one doubtful
case, who was, however, classified as indigenous owing to a lack of evidence
of contact with an imported case.
Of all reported cases (with clinical criteria) 87% (73/84) were virologically
tested between the 4th and 11th day of the onset of exanthem. Of the tested
specimens only 27% (20/73) were confirmed by identification of positive
IgM antibodies to measles. The diagnosis of measles was discarded for
the remaining 73% (53/73).
Laboratory surveillance of reported cases has markedly improved since
the start of the programme (figure 2). The measles virus was isolated
from urine in 57% (13/23) of the confirmed cases. Of the 23 confirmed
measles cases, 43% (10/23) were imported because they either arrived in
Catalonia within the incubation period or were in contact with some relatives
from abroad who were ill; 57% (13/23) were indigenous, with the last two
reported and confirmed indigenous cases being in June 1999 and July 2000
(figure 3).
Conclusion
No indigenous cases of measles occurred in Catalonia between June 1999
and July 2000. During the elimination programme for measles, it is crucial
to carry out strict active epidemiological surveillance of all reported
cases, to confirm them by laboratory data and to stop the transmission
of the virus. In the second and third year of the elimination programme,
89.7% (44/49) in 1999 and 92% (23/25) in 2000 were laboratory tested,
compared with only 60% (6/10) in the last quarter of 1998. The aim of
the programme to undertake laboratory testing of all reported cases has
been reached, if we consider those confirmed by epidemiological relation
to a laboratory confirmed case (figure 2).
It should be stressed that for all confirmed indigenous cases, their
immunisation status with respect to the measles virus was correct according
to their age (figure 4). Of the 10 confirmed imported cases, only three
had a correct immunisation status for measles according to their age (two
were younger than 15 months, and one was 33 years).
Most of the Catalan population at risk of coming into contact with an
imported measles case are correctly immunised. It is therefore probable
that there will be few or even no confirmed indigenous cases in the future.
Furthermore, whenever clinical features lead to a diagnosis of a suspected
case of measles – if this is immediately reported and serologically confirmed
– it is mandatory to investigate the possibility of foreign contacts.
This may be difficult because of the large flow of immigrants currently
arriving in Catalonia.
We may conclude that the specific procedures started
up in 1998, according to the goal set by the health plan to achieve measles
elimination in Catalonia by 31 December 2000, seem to have succeeded and
interruption of transmission of indigenous measles virus can be confirmed
in our community (16).
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