الفهرس 
Epidemiology of MeaslesOnly 14 pages are availabe for public view
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Abstract
Measles is one of the highly communicable diseases whose epidemiologic
characteristics have been well clarified long before discovery of its causative agent. It has
several characteristics which facilitate modeling including a constant incubation period, an
attack rate of almost 100% among exposed susceptibles and persistent immunity conferred
by a single attack or vaccination at the proper age with an effective vaccine.
The introduction of vaccination resulted in a change in the pattern of measles
occurrence. In situations in which routine immunization is not fully effective such as lower
than optimal immunization coverage, the disease pattern changed from endemicity in the
young age group to older age groups. This has been the situation in Egypt during the last
two decades where the age of the cases shifted to school age with occasional outbreaks /
epidemics which occur when enough susceptibles accumulate in the community especially
in large urban populations such as big cities (Cairo, Alexandria). Understanding the
dynamics of measles occurrence through modelling can contribute significantly to adopting
effective strategies and actions to anticipate epidemics and prevent them.
The aim of this study was to investigate the dynamics of measles epidemiology in
Alexandria and factors affecting its occurrence. Another objective was to apply an
appropriate model to anticipate outbreaks and suggest to national health authorities
appropriate interventions.
A retrospective study of measles in Alexandria and a case-control study of cases of
measles among school children in Alexandria (2006-2007) was carried out. For the case
control study, clinically suspected cases of measles among school children during 2006-
2007 were reviewed and cases who fitted the criteria of highly suspected measles cases and
were not diagnosed as epidemiologically linked to a laboratory diagnosed case of German
measles and were not subjected to laboratory examination for IgM were selected for this
study. An age and sex matched control for each case was selected from the same school.
An interview with the mothers of cases and controls was conducted at their homes
and detailed data were obtained for the study children and their families through a
questionnaire interview method. These data from cases and controls were analyzed to
assess the dynamics of measles in Alexandria. Further analysis and modelling was carried
out to develop a statistical method to anticipate measles outbreaks and epidemics.
The results of this study showed that:
1. Measles is endemic in Egypt with periods of epidemic increase. The inter-epidemic
period increased during the last 10 years from 3 to 4 years. It is also noted that
epidemic increases were not occurring all over Egypt at the same time.
2. There is a continued shift in the age group having measles. During the last 10 years
the proportion under 5 years (preschool age) decreased from around 40% to less
than 20% and that of the school age increased.
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3. There is evident seasonality of measles. The number of cases start to increase from
the month of October to a maximum in March/ April of next year. This seasonality
related not only to cold months but also to periods of accumulation of children in
schools.
4. The national program of measles elimination adopted by the Ministry of Health
have 3 main component: strengthening surveillance, introduction of laboratory
diagnosis and conduct of measles campaigns.
The program has 4 main performance indicators
At least 2 non measles febrile rash detected per 100,000 population. This
has been achieved.
At least 80% of all reported suspected cases of measles are adequately
investigated. This has also been achieved.
At least 80% of all suspected cases of measles are subjected to laboratory
diagnosis for the detection of Igm antibodies. This has not been achieved.
Increasing public awareness to ensure high routine immunization and
participate in supplemental campaigns. Efforts in this regard is continuing.
5. The shift from clinical to laboratory diagnosis started in 2002 as part of the national
plan for elimination and to strengthen surveillance with the requirement to examine
at least 80% of suspected cases from Igm. This rate was nearly achieved in 2005
but starting 2006, this rate decreased significantly to reach only 10.5% in 2007. it
was very low in some governorates such as in Alexandria where it was only 1.3%.
Hence the diagnosis should now be based on clinical grounds. Official reporting of
only cases confirmed by the laboratory result in a significant distortion of the
epidemiologic picture.
6. Data about cases of clinically suspected measles in Alexandria from 1988 to 2007
were fed to the MSP model developed by WHO and some other international
agencies interested in measles elimination. The immunity profile generated through
the use of the model showed a gap in infants and another gap in the age group 10
years and above.
A few options were applied using the model to assess their impact on closing the
immunity gap. It was found that the implementation of a supplemental
immunization activity in 2011 involving all secondary school children or the
immunization of all secondary school entrants for 3 consecutive years would be
capable for closing the immunity gaps in all age groups except infants by the year
2015.
7. The case control study carried out was implemented on clinically suspected cases
of measles in Alexandria which occurred in 2006 and 2007 and an age and sex
matched control. The following are the main results:
7.1 . Almost two thirds of the cases were in the preparatory schools, nearly one
thirds in primary schools and only 5.2% in secondary schools.
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7.2 . The age range of the studied cases was 7- 17 years. Two thirds of the cases
were 12 – 14 years of age.
7.3 . The majority of the cases are among birth cohorts of 1993, 1994 and 1995
who received their basic routine dose mostly in 1994 and 1995.
7.4 . The suspected source of infection was identified by the mother to be the
school in 63.4% of cases. The second main source (19.3%) was an
infected brother/sister.
7.5 . Almost all cases and controls were identified to have received the routine
dose of measles.
7.6 . The age of primary vaccination was 9 months in 73.8% of the cases and
66.2% in the controls. It was 12 months in 13.1% of cases and 20.7% for
the controls.
7.7 . A significant difference was observed between cases and controls with
respect to the number of booster doses where more than half the cases
received no booster doses while all the controls received 1 or 2 booster
doses.
7.8 . Family characteristics of the cases and controls were very similar and most
of their mothers were born before the vaccination era.
8. Reviewing the history of development of the national efforts to control or eliminate
measles shows that the birth cohort of 1993-1994 in Alexandria did not benefit
fully from the accelerated effort carried out by the Ministry of health. The
preschool campaign of 1998 targeting birth cohorts of 1993 to 1995 did not include
Alexandria as it was not considered to be at high risk. As well this same group did
not fully benefit from the campaign conducted during the school year 2000-2001 as
some may have not been enrolled in schools yet at that time.
9. The main recommendations of this study are directed to the National authorities to:
9.1. Ensure continued support including the provision of sufficient quantities of
high quality vaccines and operational expenses to meet the needs of the
elimination program.
9.2. Ensure that routine immunization against measles according to the new
schedule is not less than 95% nationally and in each province and health
district. It should be monitored regularly by accurate independent means for
at least 3 consecutive years to monitor accumulation of susceptible. With
the use of the MSP model the Ministry would be able to indentify immunity
gaps at various age groups and choose the best approach to close them.
9.3. Strengthen case based surveillance through encouraging private practice
involvement and training of staff involved in case investigation.
9.4. Laboratory support should be upgraded and possibly decentralized to ensure
that at least 80% of suspected measles cases are investigated for the
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presence of IgM. In the interim and until the target is achieved it will not be
justified to rely on the identification of only those cases confirmed by the
laboratory.
9.5. With the increase in the percent of mothers who are likely to have obtained
their immunity from vaccination, the likelihood of their babies losing their
passive immunity before the new age of primary vaccination namely one
year should be carefully monitored particularly as there is recent increase in
the proportion of cases under one year of age. This immunity gap will not
be of great importance if the gap in other age groups is closed and hence the
circulation of measles virus will be stopped.