Rotavirus infection and rotavirus serum antibody in a cohort of children from Gaza observed from birth to the age of one year

Estimating the incidence of symptomatic rotavirus infections: a systematic review and meta-analysis

BACKGROUND

We conducted for the first time a systematic review, including a meta-analysis, of the incidence of symptomatic rotavirus (RV) infections, because (1) it was shown to be an influential factor in estimating the cost-effectiveness of RV vaccination, (2) multiple community-based studies assessed it prospectively, (3) previous studies indicated, inconclusively, it might be similar around the world.

METHODOLOGY

Pubmed (which includes Medline) was searched for surveys assessing prospectively symptomatic (diarrheal) episodes in a general population and situation, which also reported on the number of the episodes being tested RV+ and on the persons and the time period observed. A bias assessment tool was developed and used according to Cochrane guidelines by 4 researchers with different backgrounds. Heterogeneity was explored graphically and by comparing fits of study-homogenous 'fixed effects' and -heterogeneous 'random effects' models. Data were synthesized using these models. Sensitivity analysis for uncertainty regarding data abstraction, bias assessment and included studies was performed.

PRINCIPAL FINDINGS

Variability between the incidences obtained from 20 studies is unlikely to be due to study groups living in different environments (tropical versus temperate climate, slums versus middle-class suburban populations), nor due to the year the study was conducted (from 1967 to 2003). A random effects model was used to incorporate unexplained heterogeneity and resulted in a global incidence estimate of 0.31 [0.19; 0.50] symptomatic RV infections per personyear of observation for children below 2 years of age, and of 0.24 [0.17; 0.34] when excluding the extreme high value of 0.84 reported for Mayan Indians in Guatemala. Apart from the inclusion/exclusion of the latter study, results were robust.

CONCLUSIONS/SIGNIFICANCE

Rather than assumptions based on an ad-hoc selection of one or two studies, these pooled estimates (together with the measure for variability between populations) should be used as an input in future cost-effectiveness analyses of RV vaccination.

Rotavirus infections in young Nicaraguan children

BACKGROUND

Rotavirus is an important cause of dehydrating diarrhea in young children throughout the world. Knowledge about frequency of reinfections, development of immunity to the virus and the possible protective effect of breast milk is important, in particular in relation to possible strategies for immunization.

METHODS

A prospective study of rotavirus infections in a cohort of 235 infants followed from birth until 2 years of age was performed in León, Nicaragua. Fecal and serum specimens were collected at specified times, and stools were also obtained during episodes of diarrhea. Fecal specimens were screened by rotavirus antigen detection and serum and colostral specimens were analyzed by isotype-specific rotavirus antibody enzyme-linked immunosorbent assay.

RESULTS

As judged by anti-rotavirus IgA antibody seroconversion and/or demonstration of rotavirus antigen in fecal specimens, > 50% of the babies had evidence of past rotavirus infection by the age of 2 months. The total incidence of rotavirus infections, including many reinfections, was 0.7 infection/child-year, of which only 17% were associated with diarrhea. The time from birth to the first demonstration of rotavirus in stool samples correlated significantly with the concentration of anti-rotavirus IgA antibodies in colostrum. There was also a tendency toward a relationship between long duration of breast-feeding and asymptomatic infection.

CONCLUSIONS

Rotavirus infections are acquired very early in infants in León, Nicaragua, and reinfections are common. Most infections are asymptomatic. Breast milk appears to confer partial protection against rotavirus infection, probably mediated by specific IgA antibodies. To be effective rotavirus vaccination would probably have to be given at a very early age to infants in developing countries.

Natural history of human rotavirus infection

Rotavirus infections occur repeatedly in humans from birth to old age. Most are asymptomatic or are associated with mild enteric symptoms. Infection in young children can be accompanied by severe life-threatening diarrhea, most commonly after primary infection. Annual childhood morbidity rates for severe diarrhea are similar worldwide. Mortality rates are low in developed countries but approach 1,000,000 annually in young children in developing countries. Rotaviruses can be classified into Groups A-E according to antigenic groups on VP6, the major capsid antigen. Only Group A,B and C rotaviruses have been shown to infect humans, and most human rotavirus disease is caused by Group A viruses. These are further classified into G and P types based on identification of antigens on the outer capsid proteins VP7 and VP4 respectively. Most severe infections in young children are caused by serotypes G1-4, and during the last two decades, G1 infections appear to have predominated worldwide. In general the more densely populated countries show the most complex patterns of occurrence of serotypes. Clinical rotavirus disease can be accompanied by shedding of > 10(12) rotavirus particles/gm feces. The virus is highly infectious and appears to retain infectivity over many months. In temperate climates, disease is most common during the colder months, when it is likely that rapid spread within families and communities occurs. Nosocomial infections are frequent, and rotaviruses can become endemic within obstetric hospital nurseries for the newborn. Few (if any) human rotavirus infections appear to be zoonoses, even though Group A rotaviruses are widespread in the young of all mammalian species. However infection of humans with reassortant rotavirus strains derived from human-animal sources can occur. The extent to which this contributes to new epidemic strains within particular countries (or worldwide) remains to be determined.