Estimating the effectiveness of early control measures through school absenteeism surveillance in observed outbreaks at rural schools in Hubei, China

BACKGROUND

School absenteeism is a common data source in syndromic surveillance, which allows for the detection of outbreaks at an early stage. Previous studies focused on its correlation with other data sources. In this study, we evaluated the effectiveness of control measures based on early warning signals from school absenteeism surveillance in rural Chinese schools.

METHODS

A school absenteeism surveillance system was established in all 17 primary schools in 3 adjacent towns in the Chinese region of Hubei. Three outbreaks (varicella, mumps, and influenza-like illness) were detected and controlled successfully from April 1, 2012, to January 15, 2014. An impulse susceptible-exposed-infectious-recovered model was used to fit the epidemics of these three outbreaks. Moreover, it simulated the potential epidemics under interventions resulting from traditional surveillance signals. The effectiveness of the absenteeism-based control measures was evaluated by comparing the simulated datasets.

RESULTS

The school absenteeism system generated 52 signals. Three outbreaks were verified through epidemiological investigation. Compared to traditional surveillance, the school absenteeism system generated simultaneous signals for the varicella outbreak, but 3 days in advance for the mumps outbreak and 2-4 days in advance for the influenza-like illness outbreak. The estimated excess protection rates of control measures based on early signals were 0.0%, 19.0-44.1%, and 29.0-37.0% for the three outbreaks, respectively.

CONCLUSIONS

Although not all outbreak control measures can benefit from early signals through school absenteeism surveillance, the effectiveness of early signal-based interventions is obvious. School absenteeism surveillance plays an important role in reducing outbreak spread.

Humoral immunity following chickenpox is influenced by geography and ethnicity

OBJECTIVES

To investigate the contribution of ethnicity and geographical location to varicella-zoster virus (VZV) serostatus and antibody concentrations.

METHODS

The presence and concentrations of antibodies to VZV were measured in 639 Bangladeshi women born in Bangladesh (BBB), 94 Bangladeshi women born in the UK (BUK) and 262 White women born in the UK (WUK). The results were analysed in relation to demographic and social data.

RESULTS

BBB women were significantly less likely to be VZV seropositive at all ages than both BUK and WUK women. However, the odds of a Bangladeshi-born woman being seropositive increased by 1.04 for each year under the age of 15 spent in the UK. In contrast, antibody concentrations were significantly lower in ethnic Bangladeshi women, irrespective of country of birth. White, but not Bangladeshi women, showed evidence of antibody boosting over time despite the latter having more exposure to children.

CONCLUSION

Geographical location during childhood is the major influence on age of primary infection with VZV while the level of antibody is related to ethnicity. Since the risk of re-infection with VZV following both natural infection and vaccination is increased as antibody concentrations fall, these results have implications for VZV vaccination programmes particularly in non-White populations.

Varicella-zoster-virus genotypes in East London: a prospective study in patients with herpes zoster

A total of 298 patients with herpes zoster were recruited as part of 2 community-based studies in East London between 1998 and 2003. Single nucleotide-polymorphism analysis of 4 regions (genes 1, 21, 37, and 60) found that most genotypes were European strains C and B, representing 58% and 21% of all samples collected. No change in the proportion of these European clades has occurred during the past 80 years, strongly supporting the hypothesis that these strains are indigenous to the United Kingdom. White patients almost exclusively had reactivation of genotypes C (66%) and B (21%), whereas patients from Africa, Asia, or the Caribbean mainly had reactivation of genotypes A and J. An increase in BglI-positive A and J genotypes in UK cases of zoster is only partly explained by immigration from endemic regions. The data presented provide a baseline against which to evaluate changes in the molecular epidemiology of varicella-zoster virus and the effect of immunization with the Japanese Oka vaccine strain.

Seroepidemiology of varicella and the reliability of a self-reported history of varicella infection in Singapore military recruits

INTRODUCTION

Varicella is an acute disease with significant morbidity. However, there is little knowledge on the seroepidemiology of the disease in Singapore. The objective of this study was to assess the seroprevalence of varicella zoster virus (VZV) antibodies in military recruits in Singapore and to ascertain the predictive value of a self-reported history of varicella. The latter is a possible proxy for seroprevalence, and may be used to provide efficient identification of candidates for vaccination.

MATERIALS AND METHODS

From September 2000 to October 2005, 2189 servicemen were selected during their pre-enlistment medical check-up. Blood samples were obtained to determine the varicella IgG levels via enzyme-linked immunosorbent assay (ELISA). Information about the participant's race, history of varicella and vaccination, and other clinical variables were obtained through a questionnaire.

RESULTS

The overall prevalence of VZV seropositivity in military recruits was 76.0% (75.8% in the 16 years to 20 years age group). For the reported history, 73.7% of Chinese participants, 73.0% of Malays, and 63.6% of Indians reported having had varicella infection and/or vaccination. Overall, the sensitivity, specificity, positive and negative predictive values of a self-reported history of varicella for serologically confirmed immunity were 87.2%, 83.2%, 94.3% and 67.1% respectively.

CONCLUSIONS

The prevalence of VZV antibodies in pre-enlistees to the Singapore Armed Forces (SAF) is high. Incidence of varicella in the SAF is on the wane, indicating an increase in herd immunity against VZV. A recalled history of varicella infection was also a good predictor of serological immunity and may be used for selection for vaccination.

Seroprevalence of antibody to varicella among Somali refugees

OBJECTIVES

To determine the seroprevalence of varicella antibody among recent Somali refugees living in Olmsted County, Minnesota, and to estimate the risk of varicella-zoster virus (VZV) infection in this group.

SUBJECTS AND METHODS

We obtained blood samples from the study subjects, along with demographic information, immunization records, and vaccine-preventable disease history. Serum samples were tested using a whole-virus IgG VZV-specific commercial enzyme-linked immunosorbent assay kit. This study was completed in 1998.

RESULTS

Overall, 200 Somali refugees, comprising 33 extended families, were interviewed, with 193 providing adequate blood samples. Thirty-five subjects (18%) were seronegative for varicelia. Males had a significantly higher seronegativity rate (25% [n = 23]) compared with females (12% [n = 12]; P = .02); however, this association disappeared after adjustment for age and varicella infection history. Five percent (5/92) of adults were seronegative compared with 30% (30/101) of all children (P < .001). Eight percent (5/61) of the adult females were seronegative, whereas none (0/31) of the adult males were seronegative. Conversely, 38% (23/60) of male children were seronegative compared with 17% (7/41) of female children (P < .001).

CONCLUSION

These results demonstrate a high prevalence of varicella seronegativity among Somali refugees who have immigrated to an endemic area. We recommend instituting improved education regarding varicella among Somali communities and increasing vaccine uptake or routine testing for serum varicella antibody to prevent VZV-related morbidity and mortality, particularly in adolescents, adult refugees, and women of childbearing age.

Varicella-related hospitalization and emergency department visit rates, before and after introduction of varicella vaccine, among white and black children in Hamilton County, Ohio

OBJECTIVE

The American Academy of Pediatrics recommended routine use of varicella vaccine in pediatric practice in 1995. We examined the impact of varicella immunization on population-based rates of pediatric varicella-related hospitalizations and emergency department (ED) visits in the years before and after introduction of varicella vaccine.

STUDY DESIGN

Discharge data for hospitalizations and ED encounters from 1990 through 2003 were queried for patients <20 years of age with varicella International Classification of Diseases, Ninth Revision, Clinical Modification codes (052.0-052.9) in any diagnostic position. Addresses were geocoded for identification of Hamilton County, Ohio, residents. Rates were calculated according to year, age, and race, with census estimates.

RESULTS

During the 14-year study period, there were 3983 incident varicella cases; 335 patients were hospitalized and 3833 were treated only in the ED. The rate of varicella-related hospitalizations decreased from 15.7 cases per 100,000 population to 5.5 cases per 100,000 population between the prevaccine period (1990-1995) and the postvaccine period (1996-2003); varicella-related ED use decreased from 178.2 cases per 100,000 population to 61.2 cases per 100,000 population. In the prevaccine period, hospitalization and ED visit rates were significantly higher for black children than for white children. In the postvaccine period, hospitalization rates did not differ according to race but ED visit rates remained significantly higher for black children, compared with white children.

CONCLUSIONS

Varicella-related hospitalization and ED visit rates decreased significantly for both white and black children in Hamilton County, Ohio, after the introduction of varicella vaccine, and the racial disparity found before licensure decreased after licensure.

Uptake of varicella vaccination among young children in the United States: a success story in eliminating racial and ethnic disparities

OBJECTIVE

To examine uptake of varicella vaccine, a live attenuated vaccine licensed in 1995 and recommended in 1996 for routine vaccination of US children 12 to 18 months of age.

METHODS

Data were for 178,616 children (19-35 months of age) and were collected in the 1997 to 2004 National Immunization Survey. The main outcome measures were estimated varicella vaccine coverage from 1997 to 2004, coverage among susceptible children (ie, those without a history of varicella disease), racial/ethnic disparities, risk factors for nonvaccination, missed opportunities to vaccinate simultaneously with other recommended vaccines, and projected increases in coverage after elimination of missed opportunities for simultaneous vaccination.

RESULTS

Varicella vaccine coverage rates increased from 26% in 1997 to 87% in 2004. State-specific coverage rates increased 44 to 80 percentage points and were >80% in 42 states and >90% in 13 states by 2004. Coverage among susceptible children increased from 62% in 1999 to 88% in 2004. From 1998 onward, no statistically significant differences in coverage were found between white and black children, whereas Hispanic children had higher coverage rates than white children in 1998 to 2001 and 2004. Risk factors for undervaccination included living in the Midwest region, living in a household with >1 child, living in nonmetropolitan areas, living below the poverty level, having a mother who did not have a college degree, and having public providers. If missed opportunities for simultaneous vaccination had been eliminated, then coverage rates would have increased from 58% to 94% in 1999 and from 87% to 96% in 2004.

CONCLUSIONS

Uptake of varicella vaccine has been steady and is an example of successful elimination of racial and ethnic disparities. Additional focus should be placed on reducing missed opportunities for simultaneous vaccination, improving coverage in rural areas and the Midwest region, and closing remaining gaps related to maternal education, provider type, and multiple-children households.

Decline in mortality due to varicella after implementation of varicella vaccination in the United States

BACKGROUND

Varicella disease has been preventable in the United States since 1995. Starting in 1999, active and passive surveillance data showed sharp decreases in varicella disease. We reviewed national death records to assess the effect of the vaccination program on mortality associated with varicella.

METHODS

Data on deaths for which varicella was listed as an underlying or contributing cause were obtained from National Center for Health Statistics Multiple Cause-of-Death Mortality Data for 1990 through 2001. We calculated the numbers and rates of death due to varicella according to age, sex, race, ethnic background, and birthplace.

RESULTS

The rate of death due to varicella fluctuated from 1990 through 1998 and then declined sharply. For the interval from 1990 through 1994, the average number of varicella-related deaths was 145 per year (varicella was listed as the underlying cause in 105 deaths and as a contributing cause in 40); it then declined to 66 per year during 1999 through 2001. For deaths for which varicella was listed as the underlying cause, age-adjusted mortality rates dropped by 66 percent, from an average of 0.41 death per 1 million population during 1990 through 1994 to 0.14 during 1999 through 2001 (P<0.001). This decline was observed in all age groups under 50 years, with the greatest reduction (92 percent) among children 1 to 4 years of age. In addition, by the period from 1999 through 2001, the average rates of mortality due to varicella among all racial and ethnic groups were below 0.15 per 1 million population, as compared with rates ranging from 0.37 per 1 million for whites to 0.66 per 1 million for other races in the period from 1990 through 1994.

CONCLUSIONS

The program of universal childhood vaccination against varicella in the United States has resulted in a sharp decline in the rate of death due to varicella.

High rate of varicella complications among Mexican-born adults in Alabama

OBJECTIVE

Our study examines risk factors for severe varicella in an outbreak among Mexican-born adults, and it compares susceptibility to infection and reliability of self-reported varicella history for these individuals with that for adults born in the United States in the outbreak locale, which may guide vaccination strategies.

METHODS

We interviewed case patients and non-case persons in the affected apartment complex and workplace, assessed disease history and susceptibility by testing for varicella-zoster virus immunoglobulin G antibodies, and reviewed the clinical data of case patients.

RESULTS

Five of 18 case patients had serious complications for which they sought medical care; 1 was hospitalized for pneumonia, and 1 was hospitalized for Guillain-Barré syndrome. Only intense exposure (e.g., sharing a bed) was marginally associated with severe disease (P=.08). In the workplace, varicella susceptibility was higher among Mexican-born workers (20%) than among workers born in the United States (3%) (adjusted prevalence odds ratio, 5.4; 95% confidence interval, 2.3-14.8). Mexican-born persons had the highest positive predictive value of self-reported disease (100%) in predicting immunity, and those born in the United States had the lowest negative predictive value of self-reported history (10%) in predicting susceptibility.

CONCLUSIONS

Varicella is a more serious disease among adults than among children, and Mexican-born adults living in the United States might have a higher risk of acquiring varicella than US-born adults. Varicella outbreaks involving adults should be prioritized for control efforts. Outbreaks can be prevented by vaccinating susceptible adults.

Varicella susceptibility and validity of history among U.S. Coast Guard recruits: an outbreak-based study

During a varicella outbreak among U.S. Coast Guard recruits, we examined varicella susceptibility serologically and evaluated validity of disease history. Recruits completed a questionnaire to obtain information on demographics, history of varicella disease, and varicella vaccination. Serological testing for varicella-zoster virus immunoglobulin G antibodies was conducted using an enzyme-linked immunosorbant assay. Among 513 recruits, 21 (4.1%) were seronegative to varicella-zoster virus. Recruits born in Puerto Rico were more likely than recruits born in the U.S. states to be susceptible (prevalence ratio, 4.3; 95% confidence interval, 1.4%, 13.1%). A positive disease history was highly predictive of positive serology (99.1%); however, 73% of those with a negative or uncertain history were also immune. Four (19%) susceptible recruits reported a positive varicella history. Although immunity among recruits was high, varicella outbreaks may occur in closed adult settings due to the high risks of exposure and transmission. Varicella vaccination can prevent these costly, disruptive outbreaks.

The molecular epidemiology of varicella-zoster virus: evidence for geographic segregation

Of 75 varicella-zoster virus (VZV) isolates obtained from patients in Africa, Asia, and the Far East, 74 (98.6%) were found to be positive for a BglI restriction site in gene 54. By contrast, <22% of strains from patients in the United Kingdom and in North and South America were positive for the BglI restriction site. Viruses positive for BglI were significantly more common in zoster occurring in patients of nonwhite origin (P<.05). Irrespective of the country in which the sample was obtained, 98% of strains positive for BglI clustered within a single phylogenetic group, which we termed "group A"; the exception was 1 strain that appeared to be recombinant genotype C/A. We used the BglI site to examine both the spread of type A viruses in the United Kingdom and the patterns of VZV infections within persons from different ethnic groups who grew up in the United Kingdom or abroad.

Incidence and hospitalization rates of varicella and herpes zoster before varicella vaccine introduction: a baseline assessment of the shifting epidemiology of varicella disease

BACKGROUND

A 15-year postmarketing evaluation of the impact of varicella vaccine on the age distribution of varicella disease is being conducted at Kaiser Permanente Medical Care Program, Northern California (KPMCP). We report on a baseline assessment of the age-specific incidence and hospitalization rates of varicella and herpes zoster that was conducted before vaccine introduction.

METHODS

To assess the annual incidence of varicella, a telephone survey was conducted in a random sample of approximately 8,000 youths 5 to 19 years of age. The annual incidence of hospitalizations for varicella and herpes zoster in 1994 was assessed with the use of the computerized database at KPMCP.

RESULTS

Varicella annual incidence was 10.3% in 5- to 9-year-olds, 1.9% in 10- to 14-year-olds and 1.2% in the 15- to 19-year age groups, respectively. Hospitalization rates among the entire KPMCP membership were 2.6 and 2.1 per 100,000 person years for varicella and zoster, respectively. Varicella incidence in the 15- to 19-year age group was higher among African-Americans than among Caucasians.

CONCLUSIONS

Varicella rates were similar in the 5- to 9- and 10- to 14-year age groups to rates from other published studies conducted in 1972 to 1978, 1980 to 1988 and 1990 to 1992; however, the rate in 15- to 19-year-olds was 2 to 4 times higher than published rates in the same age category.

Epidemiology of primary varicella and herpes zoster hospitalizations: the pre-varicella vaccine era

To determine the epidemiology and costs of hospitalization with primary varicella and herpes zoster in the prevaccine era and the usefulness of hospital discharge data to determine the population impact of vaccination on these conditions, statewide hospital discharge data in Connecticut from 1986 to 1995 were analyzed. Annual hospitalizations for herpes zoster were 4-fold higher than for primary varicella (16.1 vs. 4.1/100,000). Overall, 69% and 83%, respectively, had no underlying immunosuppressive conditions. Regarding primary varicella, 53% of patients were aged <15 years, there was a marked winter-spring seasonality, and Hispanics and blacks were 4.1 and 2.6 times more likely than whites to be hospitalized. Regarding herpes zoster, 66.9% of patients were aged >64 years, and there was no seasonality. The mean patient charges in 1995 were $12,819 for primary varicella and $15,583 for herpes zoster. Analysis of population-based hospital discharge data is a feasible means of monitoring the impact of varicella immunization on severe morbidity due to primary varicella and herpes zoster.

Ethnic differences in the severity of varicella in adults in northern Saudi Arabia

The severity of varicella infection in 124 expatriates from the Asian continent was compared to that in 120 Saudi nationals, seen in Arar Central Hospital, Arar, Saudi Arabia, between January 1992 and December 1994. Persistent fever (defined as a raised body temperature more than 37.4 degrees C lasting more than 5 days), extensive skin eruptions (defined as extensive, when more than 50% of the body surface was affected) and transient elevation of hepatic enzymes (aspartate transaminases > 37 U/L and alanine transaminases > 40 U/L) after excluding other possible causes, occurred significantly more in expatriates than in Saudis. The mean duration of the illness in expatriates was 15.9 +/- 3.41 days as compared to a mean duration of 13.1 +/- 3.52 days in Saudis. This difference was statistically significant (p < 0.01 Student's t-test). The findings in this study suggest that varicella infection runs a more severe course in expatriates from the Asian continent as compared to the Saudis. Treatment with the antiviral agent acyclovir may be indicated in this group of expatriates with varicella infection.

Common infectious diseases in a population with low multiple sclerosis and varicella occurrence

A previous study revealed the rarity of varicella zoster virus (VZV) diseases among 5601 Hutterite Brethren living in a high-risk area for these diseases. The current study was established to determine the frequency of other common infectious diseases. The information was gathered from a population-based study of a unique group of Manitoba citizens and compared with an equal number of their age and sex-matched neighbors. The data were contained in the records of the Manitoba Health Services Commission (MHSC). The MHSC, the sole paying agency for medical diseases in Manitoba, contained 94,383,972 records for all of Manitoba for the years 1985 to 1991 inclusive. From these, the records of a cohort of 5601 Hutterites and an equal number of non-Hutterite age- and sex-matched controls were examined for the frequency of 14 diseases of interest. To be eligible a Hutterite subject must have one of the 22 unique family names and live on a Colony with the precise address. A control must be age (within 10 years) and sex-matched, live in the same or a contiguous postal code, and use the same medical practitioners. There were no interventions or identification of any member of the study. Mumps, acute coryza, and rubella are of the same frequency among the two groups. Only herpes simplex and cellulitis are more common among the Hutterites. All of the other nine common infectious diseases are significantly more common among the controls. The VZV diseases are not exclusively less common among the Hutterite Brethren. Nine other common infectious diseases are also less common but the degree of significant difference does not reach the level of the VZV diseases. The reduction in numbers of these diseases among the Hutterites is not related to the vaccination habits of the group and is not due to physical isolation. The Hutterites appear to have a more effective immune system relative to their neighbors.

Varicella zoster virus and multiple sclerosis in a Hutterite population

There are similarities between multiple sclerosis and varicella. They are common in the same parts of the world and both are scarce in other areas. Immigration studies suggest the environmental cause of multiple sclerosis (MS) must be contracted prior to age 15 years and will usually remain dormant for years. At age 10 years varicella has occurred in greater than 95% of children living in the high-risk areas for both of these diseases. The varicella zoster virus (VZV) could be etiologically important in multiple sclerosis. The known host containment of the virus for decades with recrudescence and the variable cell-mediated immunity of the host, which can wax and wane without clinical manifestations, all lend themselves to the natural history of multiple sclerosis. A population-based study of the medical records of 5601 Hutterite Brethren was performed to determine the occurrence of multiple sclerosis, varicella, and herpes zoster. Compared to their matched non-Hutterite neighbors who acted as controls, these events were significantly less common among the Hutterites. Included in the study was an assessment of other common neurological diseases and "autoimmune" diseases among the Hutterites and the controls. There is evidence of a relationship between MS and VZV that may not be coincidental.

Varicella among immigrants from the tropics, a health problem

The incidence of varicella in Tamil refugees in Denmark was evaluated. Of 256 Tamils, 44% developed varicella infection in the first few months after arrival, representing 38% of the adults, and 68% of the children. During approximately four months' observation in Denmark, 75% of the refugees with no history of varicella developed a typical infection whereas only 2% of those with a history of varicella developed the disease. Tropical refugees with a negative history of varicella must therefore be considered nonimmune. Nine of 44 fertile women were pregnant. Two acquired the varicella infection during the first-trimester, none in relation to delivery. By organizing a health-check on arrival, prophylactic measures can reduce the health hazard of varicella infection in refugees from the tropics.

Varicella outbreaks in Army recruits from Puerto Rico. Varicella susceptibility in a population from the tropics

Two outbreaks of varicella consisting of a total of 105 cases occurred in a highly varicella-susceptible population of young adult Army recruits from Puerto Rico enrolled in the Defense Language Institute in San Antonio, Tex, between October 1986 and November 1987. Epidemiologic investigation found a significantly higher risk for enlisted recruits housed in open barracks than for officers housed in private rooms. The attack rate in the first outbreak was 30%, with an estimated attack rate of 71% among susceptible persons. Serologic testing of 810 adult recruits from Puerto Rico for varicella-zoster antibody by means of an enzyme-linked immunosorbent assay procedure found 42% to be seronegative, with no significant difference by sex. The enzyme-linked immunosorbent assay test had a positive predictive value for absence of disease development of 95% in the second outbreak. Serologic test results were successfully used as part of the outbreak control strategy, with a resultant decrease in attack rates to 19% overall and 30% among susceptible persons in the second outbreak. Uniquely susceptible adult populations placed in conditions with high likelihood of infection on exposure are potential candidates for the varicella vaccine after its licensure.