Descriptive epidemiology is defined as the study of the amount and distribution of disease within a population by person, place, and time.
Descriptive epidemiology answers the following questions: Who is affected? Where and when do cases occur? It describes cases by person, place, and time (TUI University 2008).Introduction Descriptive epidemiology focuses on both the pattern of health events as well as on their frequency in popuations. Within the field of epidemiology, there are three types of data that are necessary for describing the patterns of health and disease in human populations. These three pillars of descriptive epidemiologic analysis are Person, Place, and Time.
Described data by person, place, and time Lyme disease is an acute inflammatory disease characterized by a rash with joint swelling and fever caused by bacteria carried by the bite of tick. Symptoms include a rash followed by fever, joint pain, and headaches, affects the nervous system and heart. During 1992--1998, data regarding reported cases of Lyme disease included county and state of residence, age, sex, and date of onset. Person characterisitics include socio-dempgraphic characteristics such as age, gender and healthcare services.
Information regarding age was available for 86,425 reported cases.The median age was 39 years ranging from ages 1-100 years. The highest reported incident occurred in children aged 5-9 years and adults 40-45 years. Crude mean was 4.
8/100,000 male and 4.3/100,000 females. For children and adolescents aged 5-19 years, and adults aged less than or equal to 60 years, reported higher among males. For all other groups, reported incidence was approximately equal among males and females.
Gender. The reported incidence is higher for females than for males. The gender discrepancy may be attributable to increases in exposure to infected ticks, less use of personal protective measures, and men may tend to report symptoms less often than women.However, due to increased healthcare services for the illness of Lyme disease, passive reporting is initiated when a health-care provider makes a diagnosis of Lyme disease and reports that case to the local public health office or directly to the state health department.
State health departments report to the CDC and through the NETSS. With reporting results it provides a basis for evaluating and target prevention efforts. Place characteristics include geographic location, features of the geography, population density, and health facilities. Lyme disease has a highly focal distribution with the US, the top 10% of countries reported approximately 92% of cases from which county of residence are predominantly located in eight northeastern states; Connecticut, Delaware, Maryland, Massachusetts New Jersey, New York, Pennsylvania, and Rhode Island and two north-central states Minnesota and Wisconsin.Naturally, anyone who is regularly outside in areas where tick rates are high has a greater than average risk for becoming infected.
In such areas, between 1 - 3% of people who live there become infected at some time. New York has had the highest number of total cases to date, followed by Connecticut, which actually has the highest number of infected patients per total population. Pennsylvania and New Jersey have the next highest infection rates. One analysis suggested the risk for Lyme disease exposure is highest in wet, green areas, and lower in areas with lawns or low vegetation. Hiking and camping in the Northeastern woods carries a significant risk for tick bites and Lyme disease.
The disease is not limited to rural settings.It is becoming increasingly common in suburban areas. Beaches are also home to ticks. Time characteristics include cyclical changes, long term secular trends, and even daily or hourly occurrences during an epidemic. While person characteristics are attributes of individuals, place and time characteristics are attributes of the physical and social environment.
Majority of cases reported was in June, July, and August. This is consistent with the results of the results of other epidemiologic studies and corresponds with the seasonal feeding activity of ticks in the Northeastern United States.In addition June, July, and August are the months when humans most commonly engage in outdoor activities. The time of year of highest risk depends on the geographical region. Northeast and North Central U.S.
In the northeastern and north central U.S., most cases of Lyme disease are reported from May through August, with July being the peak month. Exceptions may occur in years of warm winters and wet springs, which can bring the deer tick nymphs out about 2 weeks earlier. This same climate also creates the wet, green environment that increases the prevalence of ticks.Possible explanations for the pattern of this disease An environmental explanation for regional Lyme disease variability, such as weather is proposed because similar annual patterns of tick infection rates have been observed in forests dominated by species other than oaks and in regions without forests.
The disease is transmitted by a "black-legged" tick with the life cycle of 2 years to complete in northern US latitudes. In the US Northeast, variations in the tick life cycle are present, but oviposition (egg-laying) tends to begin in May, and larvae are most abundant in the summer months. Tick larvae feed chiefly on small mammals such as the white-footed mouse which can transmit the Lyme disease agent to the tick.Following feeding, the larvae eventually enter a dormant condition for much of the winter.
The surviving larvae molt into nymphs in late spring and will seek suitable hosts, including humans, at that time. In the US Northeast, approximately two thirds of human Lyme disease infections are transmitted during the months of June and July by infected nymphs in the second year of the tick life cycle. Ticks require a relatively humid microclimate, such as decomposing plant matter, and soil humidity will affect their survival, particularly during quiescence and dormancy. A recent study in northern Illinois found a significant relation between cumulative rainfall and tick density and tick infection rates.
Previous laboratory research demonstrated the low tolerance of ticks to dry weather throughout its life cycle.Conclusion In the future, Lyme disease surveillance, enhanced by laboratory reporting and expanded active surveillance, will be important in evaluating temporal and geographic trends and should be used to monitor the effectiveness of preventive interventions.Referenceshttp://www.cdc.gov/mmwr/preview/mmwrhtml/ss4903a1.htmhttp://www.umm.edu/patiented/articles/who_gets_lyme_disease_when_000016_3.htmhttp://aje.oxfordjournals.org/cgi/content/full/157/6/531http://library.downstate.edu/EBM2/2100.htmhttp://jcm.asm.org/cgi/content/full/39/8/2954
