Modified Clinical Manifestations of Measles in Young Infants: 10 Years' Experience in a Tertiary Referral Centre of Hong Kong

Background: Measles still causes significant morbidity and mortality. The diagnosis of measles relies on early recognition of clinical manifestations. We identified a group of young infants who presented with a modified clinical picture after contracting measles, but there is scarce literature describing this observation. Method: We conducted a retrospective study of all infants <1 year old with measles confirmed by serological or virological methods in Princess Margaret Hospital, a territory-wide tertiary referral centre for infectious diseases in Hong Kong, over a period of 10 years from 1999 to 2008. The study population (n=165) was divided into 2 groups: 29 infants were aged <7 months and 136 infants were 7-12 months of age. Their clinical manifestations were compared and analysed, which included the timing of skin rash in relation to onset of fever, duration of fever, presence or absence of characteristic clinical features of measles such as coryza, cough, conjunctivitis, Koplik's spots, staining of convalescent rash, and other associated features and complications. Results: The mean duration of fever in infants aged <7 months and 7-12 months were 4.6 and 6.8 days, respectively (p<0.001, 95% CI 1.24-3.04). Shorter duration of fever was noted in the younger age group with a positive correlation observed for age and duration of fever (r=0.307, p<0.001). The onset of skin rash was 2.3 and 3.7 days after the onset of fever for the 2 age groups, respectively (p=0.00, 95% CI 0.58-2.12). Earlier onset of skin rash was noted in the younger age group with a positive con-elation observed for age and timing of skin rash from the onset of fever (r=0.255, p=0.001). Conjunctivitis (p=0.001) and staining of skin rash during convalescence (p=0.026) were significantly less common in the younger infant group. There were no significant differences between the 2 groups regarding presence of coryza (p=0.07), cough (p=0.28). Koplik's spots (p=0.18), diarrhoea (p=0.72), pneumonia (p=0.74) and the use of antibiotics (p=0.74). Conclusion: Our study revealed a modified clinical picture of non-specific and milder form of measles in young infants. The presence of modified features may be due to partial protection provided by maternally derived measles antibody (anti-measles IgG). We should maintain a high index of suspicion for measles presenting in this group of patients because of the possibility of atypical presentation. The use of rapid diagnostic test (e.g. anti-measles IgM) in such situation facilitates early diagnosis, proper treatment and institution of appropriate infection control measures. Early airborne isolation of hospitalised infants should be considered in all suspected cases to interrupt transmission and prevent potential nosocomial outbreaks.