"a decrease in cases" is correct and usable in written English
You can use it to refer to a decrease in the number of cases of something, such as a disease or a type of crime. For example, "There has been a decrease in cases of identity theft across the country."
The chief justice said the decline came mainly from a decrease in cases involving the Board of Immigration Appeals.
"We'd love to see a decrease in cases, but in the past there have been outbreaks of seasonal influenza even in summer camps," said Dr. Anne Schuchat, the agency's interim deputy director for public health.
Despite signs that the pandemic may be slowing – latest figures show a decrease in cases – Sir Liam said its severity in very young children appeared to be increasing, with 176 in hospital, a rate three times that in adults and 19 in critical care.
Early data from the Fall wave of the H1N1/09 outbreak in the United States already shows a trend towards a decrease in cases in school-age children [64].
Secondly, our report indicates that actively informing the public about RAS can cause a decrease in cases.
Although there was AB persistency, a decrease in cases was achieved before reaching an epidemic level causing units to be shut down.
The epidemic curve in their article suggests that the control activities had an effect on mortality rates, resulting in a decrease in case-fatality rates to <1%.
These trends might reflect a progressive increase in unknown breast cancer exposure and a decrease in case fatality due to better treatment.
Since then mortality from myocardial infarction and stroke has decreased [ONS 1985–1995 [ 12] versus ONS 2010 [ 2]; column 3 in Table 4 (Appendix)] as a result of both a decrease in incidence and a decrease in case-fatality.
Two studies [ 13, 14] reported the contributions to the decrease in mortality arising from a decrease in incidence (I) compared with a decrease in case fatality (CF) (column 4 in Table 4 (Appendix)).
Such a decrease in case-fatality rate is typical of human adaptation [ 28] and is in line with the theory that the majority of human pathogens arose only after the advent of agriculture and originate from animal pathogens: they were initially responsible for zoonoses and later adapted to the human hosts, due to co-habitation between animals and humans and to human crowding [ 32].
