Laboratory reports of Haemophilus influenzae by age group and serotype, England: annual 2021 (and 2020)
Updated 15 August 2023
Applies to England
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During 2021 (January to December inclusive), there were 344 laboratory-confirmed cases of invasive Haemophilus influenzae (Hi). This was with the same number of cases as in 2020 (Table 1), but a 42% decrease compared to the 591 confirmed cases in 2019 (not shown). The coronavirus (COVID-19) pandemic restrictions were associated with reductions in a number of infections including invasive Haemophilus influenzae disease during 2020 (1), and cases remained low during 2021.
All isolates in 2021 and 2020 were serotyped. Most isolates were non-encapsulated Haemophilus influenzae (ncHi) (76%), although this proportion was lower compared to 87% in 2020. In 2021, there were 7 cases (2%) of invasive H. influenzae serotype b (Hib) disease, similar to 2020 (n=6). In 2020, all Hib cases were identified in adults, whilst 2 of the cases in 2021 were in children under the age of 5 years. Other serotypes causing invasive disease (24%) in 2021 included: 55 serotype f, 12 serotype a and 7 serotype e. In 2020, other serotypes only accounted for 13% of all cases due to a higher number of ncHi cases (Table 1).
Most invasive H. influenzae infections (82%) in 2021 were are in adults aged 15 years and over (Table 1). Cases in infants aged less than 1 year declined in 2021 compared to 2020, whilst there was a slight increase in the number and proportion of cases in 1 to 4 and 5 to 14 year-olds (Table 1). Despite this distribution, the incidence remains higher in under 5s compared to persons aged 5 years and older (3.0 per 100,000 and 0.5 per 100,000 respectively in 2021) but is very low overall (1.0 per 100,000 persons in 2020 and 0.6 per 100,000 in 2021).
There were no deaths attributed to invasive Hib disease in 2020 and 2021. The most recent death attributed to invasive Hib disease in an adult was in 2015, and in a child in 2011.
As reported previously (2), cases of invasive Hib disease have declined since the introduction of the Hib conjugate vaccine in 1992 and have remained at low levels since the introduction of the 12-month booster in 2006 (Figure 1). In 2021, invasive Hib disease continued to be well controlled across all age groups.
Table 1. Number of Haemophilus influenzae cases by serotype and age group, England, 2020 and 2021.
(‘Not typed’ refers to samples that have not been received at the reference laboratory for typing.)
| Type | <1 year: 2020 | <1 year: 2021 | 1 to 4 years: 2020 | 1 to 4 years: 2021 | 5 to 14 years: 2020 | 5 to 14 years: 2021 | 15+ years: 2020 | 15+ years: 2021 | Total 2020 | Total 2021 |
|---|---|---|---|---|---|---|---|---|---|---|
| b | 0 | 1 | 0 | 1 | 0 | 0 | 6 | 5 | 6 | 7 |
| Non capsulated | 31 | 14 | 16 | 17 | 2 | 10 | 249 | 222 | 298 | 265 |
| a,e,f | 5 | 4 | 5 | 10 | 2 | 4 | 28 | 56 | 40 | 72 |
| Not typed [Note 1] | 5 | 3 | 0 | 0 | 1 | 1 | 50 | 39 | 56 | 43 |
| Total | 41 | 22 | 21 | 28 | 5 | 15 | 333 | 322 | 400 | 387 |
Note 1. The numbers for “not serotyped cases” in this table were corrected in August 2023.
Figure 1. Total cases of Hib by year, 2000 to 2021
References
1. Brueggemann AB, Jansen van Rensburg MJ, Shaw D, McCarthy ND, Jolley KA, Maiden MCJ, and others (2021). Changes in the incidence of invasive disease due to Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis during the COVID-19 pandemic in 26 countries and territories in the Invasive Respiratory Infection Surveillance Initiative: a prospective analysis of surveillance data. The Lancet Digital Health: volume 3, issue 6
2. Laboratory reports of Haemophilus influenzae by age group and serotype (England and Wales): annual report for 2015. Health Protection Report: volume 10 issue 8