Diphtheria outbreak in Cox’s Bazar Bangladesh, 2017–18. Each line
shows the number of new cases on a given day, as reported in the
database as it appeared on 9 December, 19 December and 8
January.
Data: Finger et al., 2019Although outbreak data can be unreliable, it doesn’t mean it’s
unusable. Imperfect data isn’t necessarily a problem if we know how
it’s imperfect, and can adjust accordingly. For example, suppose your
watch is an hour slow. If you aren’t aware of this, it will probably
cause you problems. But if you know about the delay, you can make
a mental adjustment and still be on time. Likewise, if we know the
delay in reporting during an outbreak, we can adjust how we interpret
the outbreak curve. Such ‘nowcasting’, which aims to understand the
situation as it currently stands, is often necessary before forecasts
can be made.
Our ability to nowcast will depend on the length of the delay and
the quality of data available. Many infectious disease outbreaks last
weeks or months, but other outbreaks can occur on much longer
timescales. Take the so-called opioid epidemic in the US, in which a
rising number of people are addicted to prescription painkillers, as
well as illegal drugs like heroin. Drug overdoses are now the leading
cause of death for Americans under the age of 55. As a result of
these additional deaths, average life expectancy in the US declined