Do not use accents for words that can be correct without them (e.g., naive, debride).
Use an apostrophe to indicate possession. If the possessor is plural, the apostrophe comes after the plural –s.
the patient’s symptoms
6 months’ gestation
Pronominal possessives (his, hers, yours, theirs, ours, its) do not take an apostrophe. (It’s is a contraction of it is.)
Year indications are not possessive.
1960s not 1960's
Diseases, syndromes, tests, or compounds that are named after a person or place are not possessive. Official animal names, however, may retain apostrophes (see http://www.itis.gov/ for animal names).
Student t test
Eagle minimal essential medium
Exceptions: Legionnaires’ disease, woolsorters’ disease
Avoid the following eponyms:
Reiter syndrome (use reactive arthritis)
Wegener's granulomatosis (use vasculitis or ANCA-associated granulomatous vasculitis)
Note: ANCA = antineutrophil cytoplasmic antibodies
A colon may be used, sparingly, to introduce a list or series. Do not capitalize the first word after a colon (unless it would be capitalized for other reasons, such as beginning a sentence or a subtitle). Do not use a colon to introduce a series of complete sentences; change the colon to a period or edit the list so that it is no longer made up of complete sentences.
Incorrect: Cells were prepared as follows: Strain 12B was grown in G broth. Cells were harvested by centrifugation. The pellet was dissolved in solution Y.
Correct: Cells were prepared as follows. Strain 12 B was grown in G broth. Cells were harvested by centrifugation. The pellet was dissolved in solution Y.
Correct: Cells were prepared as follows: strain 12B was grown in G broth, cells were harvested by centrifugation, and the pellet was dissolved in solution Y.
If any item in a list includes a complete sentence that gives information about that item only, either edit out the colon or put the additional information in parentheses.
Incorrect: This conclusion is based on the following results: 1) The mapping of the mutations between 0.13 and 0.23 map unit. This finding indicates that they lie within a 1.2-kbp region. 2) The presence of the Nif phenotype in all the mutants.
Correct: This conclusion is based on the following results: 1) the mapping of the mutations between 0.13 and 0.23 map unit (this indicates that they lie within a 1.2-kbp region) and 2) the presence of the Nif phenotype.
Do not use a colon if the items in the list complete the sentence grammatically.
Incorrect: XYZ medium contained: A, B, and C.
Correct: XYZ medium contained A, B, and C.
Commas are required in the following situations:
before the conjunction in a compound sentence if both clauses are independent.
Incorrect: All culture results were negative for S. pneumoniae, and were omitted from multivariate analysis.
Correct: All culture results were negative for S. pneumoniae and were omitted from multivariate analysis.
Correct: All culture results were negative for S. pneumoniae, and they were omitted from multivariate analysis.
after all items linked by and or or in a series, including the item before the conjunction.
after state when city is mentioned in text.
in Dallas, Texas, in 1995
after date that gives month, day, and year in text.
Comma needed: The test given January 1, 1997, showed that…
Comma not needed: The test given in January 1997 showed that
after an introductory phrase of >5 words; a comma can be used after fewer words if necessary to clarify the meaning.
after i.e. and e.g.
in numerals >999 (e.g., 100,000)
Avoid em-dashes (—) in scientific writing. Their use is for sudden breaks in thought that change the sentence structure or amplify and expand a phrase in the main clause. Try parentheses instead.
Use an en-dash (–) to connect numbers in a range. Use a hyphen, not an en dash, between numbers that are not inclusive (e.g., phone numbers and grant numbers).
Use an en-dash to indicate negative values (–70°C).
Use between compound adjectives when 1 element is an open compound, when >2 elements are hyphenated compounds, or in complex modifying phrases that include suffixes and prefixes and hyphens.
New York–Boston connector
Reverse transcription PCR
In complex modifying phrases that include suffixes or prefixes, hyphens and en-dashes are sometimes used to avoid ambiguity.
Terms formed by combining >2 words or elements of words may be open (with a space between them), hyphenated, or solid (as 1 word). If in doubt about how to treat a compound, consult Merriam-Webster’s or Dorland’s dictionaries. Below is a list of common terms.
acute-phase serum samples
age group (2 words)
antimicrobial drug resistance
bed net (n), bed-net (adj)
child care (n), childcare (ajd)
cut off (v), cutoff (adj)
day care (n), daycare (adj)
follow-up (n), follow up (v)
fresh water (n), freshwater (adj)
HPV-16, hyphenate when the type is included
long term (n), long-term (adj)
maximum-likelihood (as adj only)
maximum-parsimony (as adj only)
neighbor-joining (ad adj only)
plaque-reduction neutralization test
pulsed-field gel electrophoresis
real-time reverse transcription PCR
restriction fragment length polymorphism
Robert Koch Institute
short term (n), short-term (adj)
ST5 (i.e., sequence type 5)
stand by (v), standby (adj)
t cell (n), t-cell (adj)
variable number tandem repeat
website, web page
well-known person, but he is well known
whole-genome sequencing (i.e., the term is hyphenated only when used as an adjective describing another term)
work-up (n), work up (v)
Common and unambiguous compound adjectives need not be hyphenated. Ethnic designations are never hyphenated, even when used adjectivally.
food safety issues, foodborne illness study, public health nurse
African American patients, French Canadian ancestry, Asian American participants
Below is a list of common prefixes. They should always be closed up with the root word, except as noted.
before a capital letter (un-American, sub-Saharan)
before an abbreviation or acronym (non-mRNA)
before a numeral (pre-1970)
to avoid confusion with a similar unhyphenated word (re-cover, re-creation)
to avoid a confusing meaning, as in immunologic terms such as anti-rabbit, anti-goat, anti-mouse, anti-human. Goat anti-rabbit IgG means goat antiserum against rabbit IgG, not goat IgG that is antirabbit.
Even if letters are doubled, common prefixes are usually not joined by hyphens.
Always hyphenate the prefixes self- and cross-.
self-aware, self-sticking, cross-react
Similarly, most common suffixes are joined without a hyphen, such as -fold, -hood, -less, -like, -wide, and -wise, unless doing so creates an unclear or excessively long word, triples a consonant (bell-like), follows a proper noun (Whitman-like), or follows a number (10-fold, 2.5-fold).
Exception: Hyphenate –like for words with >1 syllable, unless the word ends with L.
Hyphenate all words with the –borne suffix. Exceptions are those listed in Merriam-Webster dictionary as 1 word (airborne, foodborne, waterborne).
For words with a prefix that modifies a hyphenated term, use hyphen for primary construction and en-dash for secondary construction. In the following example, non- modifies mosquito-borne, not just mosquito so the en-dash is used.
Non–mosquito-borne, not nonmosquito-borne
Do not hyphenate after an adverb ending in –ly, even when used in a compound modifier preceding the word modified.
The rapidly rising temperature caused…
Do not hyphenate foreign phrases that are printed open in other circumstances (e.g., in vitro translation, in situ protein synthesis, in vitro–stimulated growth, in situ–synthesized proteins).
Do not hyphenate CDC mailstops.
Nested parentheses sometimes appear in chemical names, usage is dependent on the author’s discretion as to how to best use them.
If a designation that already contains parentheses must be enclosed within parentheses, do not change the designation. Instead, use brackets in place of the outer set of parentheses.
Incorrect: another strain (strain 123[pXYZ])
Incorrect: another strain (strain 123(pXYZ))
Correct: another strain [strain 123(pXYZ)]
If a reference falls inside a parenthetical statement, separate it from other material with a semicolon. Do not enclose the reference number in brackets.
The procedure we used (the Lowry method; 12)…
(21; Table 1)
When multiple tables or figures are enclosed within the same parentheses, use semicolons, not the word and.
(Tables 1; 2) ¬
(Table 3; Figure 2)
Exception: use a semicolon between print and online tables and figures (with or without URL) or between figure panels and another graphic (figure or table).
(Table 3; online Appendix Figure 2)
(Figure 3, panel B; Table 4)
Avoid numbered lists if possible. If a numbered list is necessary for clarity, use a single parenthesis to avoid confusion with references. Separate elements with commas, unless commas are used within elements, in which case semicolons should be used.
Three procedures were instituted hospitalwide: 1) handwashing, which is associated with fewer nosocomial infections; 2) isolation precautions, according to established guidelines; and 3) mandatory screening of staff.
Periods are omitted from some abbreviations
but not others.
e.g., i.e. (use only within parentheses)
Joseph E. Filmore
Email addresses or URLs in references are not followed by a period.
For an ellipsis, use the Microsoft Word character (…) rather than 3 periods separated by spaces.
Use a period for a decimal (23.7), not a comma (European style).
Semicolons are used to separate 2 independent clauses when no conjunction is used.
Guadalupe is a young community; 81% of houses were built in the past 20 years.
Guadalupe is a young community, and 81% of houses were built in the past 20 years.
Semicolons are also used to separate items in a series if internal punctuation is present.
Exclusion criteria included tobacco use; history of asthma, COPD, or lung cancer; pregnancy or intent to become pregnant; and inability to give informed consent.
Use of a virgule implies duality.
The physician/patient experience implies that the physician and patient are one and the same.
The physician–patient relationship implies 2 different persons.
Correct: HIV/TB co-infection (because they equally describe the co-infection)
Avoid: HIV/AIDS (because they are not the same)
He or she, not he/she
Father and son bowling league, not father/son bowling league
Avoid and/or; most of the time simply and or or is appropriate.
Do use a virgule for drug combinations.
- Page created: February 04, 2010
- Page last updated: May 10, 2016
- Page last reviewed: May 10, 2016
- Centers for Disease Control and Prevention,
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
Office of the Director (OD)