Community-based epidemiological studies on measles in Karachi, Pakistan

Endemic measles in Karachi, Pakistan and validation of IMCI criteria for measles

AIM

To estimate the incidence of measles in Karachi, Pakistan and to determine the proportion of children with measles based on the WHO integrated management of childhood illness (IMCI) criteria with a positive IgM for measles or dengue.

METHODS

Patients up to 14 years old were screened for febrile rash illnesses at five Karachi hospitals. Active measles cases were classified as measles, measles with eye and mouth complications, or severe complicated measles using IMCI criteria.

RESULTS

Screening 1,219,061 patients over a 39-month period identified 3503 qualified children. Most (76.8%) measles cases occurred in children under five years of age. The average annual incidence rate was 0.68 per 1000 in year 1; 0.19 in year 2 and 0.08 in year 3 of surveillance. Pneumonia and diarrhoea were the most common complications. Of 18.1% hospitalized, 1.6% died. Of 2286 children tested, 1599 (69.9%) were measles IgM positive. Of 542 measles IgM negative children, 66 (12%) were dengue IgM positive. The predictive positive value for the IMCI case definition was 75%.

CONCLUSION

The IMCI case definitions for measles is reasonable but may overestimate measles incidence. Measles continues to be a public health problem in Pakistan; increased efforts to control measles are urgently needed.

Maternal measles antibody decay in rural Bangladeshi infants--implications for vaccination schedules

Considerable numbers of measles cases occur below the target age for vaccination in the Indian sub-continent. The immunogenicity of measles vaccine in infancy is dependent on the rate of decay in maternal antibody since this antibody interferes with vaccine induced seroconversion. This study investigated maternal antibody decay in a rural population in Bangladesh and evaluated possible risk factors for early decay. Measles antibodies were assessed using both ELISA and Plaque Reduction Neutralization (PRN) test in 330 infant-mother pairs in a cross-sectional survey. PRN was more sensitive method than ELISA for determining antibody levels. Antibody levels decreased rapidly in infants with increasing age. By the age of 5 months, 67% (28/42) infants had practically no protective antibody left (30 mIU ml-1 or below). Only 12% infants at 5 months of age, and 5% at 8 months, had levels greater than 120 mIU ml-1--stated to 'protect' children. Multiple regression showed that maternal age was the only variable associated with the level of antibody (maternal weight, height and MUAC were not associated), decreasing by 1.06 mIU ml-1 for each year of age (P = 0.002). Infant's antibody concentration decreased with age by an average 2 mIU mL-1 for every month of life (P < 0.0001), and was determined by the maternal antibody concentration (P < 0.0001) (child's length, weight, MUAC, mother's gestational age and parity were not associated). The relatively rapid antibody decay suggests that the target age for measles vaccination might be reduced. Further, as the cohort of vaccinated mothers enters reproductive age in Bangladesh, a more rapid decay of antibody may be expected in future generations of Bangladeshi children. The information presented here suggests that a formal trial of standard measles vaccine at younger ages is justified in this population as it could confer considerable benefit in reducing infant measles.